* General Information / Basics * Oldsmobile Distributors * Ignition Types
* Points to HEI Ignition Conversion
* Tuning

Submit corrections and additions to this information to The Olds FAQ Compiler.

General Information / Basics

Checking Valve Timing

Found out how to check valve timing and/or timing chain stretch WITHOUT removing the front cover today.

Remove the distributor cap, right valve cover and the #4 cyl rocker arms and pedestal. turn engine to TDC on the #4 cyl (rotor pionting to #4 and timing mark on balancer lined up with 0 on the pointer).

Set up a dial gauge on the #4 intake push rod.

Rotate the engine to TDC #1 cylinder.

These #s are for stock engines and wouldn't work for engines with aftermarket cams.

[ Thanks to Bob Blanchard for this information. ]

Corona Effect

The Corona Effect is what causes neon signs to work. By inducing high voltage in the tube, the gas is ionized and thereby lights up. In the case of plug wires glowing, the Corona effect can happen when atmospheric conditions are right. High humidity and low barometric pressure combined with the high voltage of the ignition system will create an electrostatic field around the plug wires and will in effect, ionize the ~air~ around the plug wires. Thereby causing the glow. Since this is a breakdown of the surrounding air (not the wires) it will not affect ignition performance. That is of course assuming your plug wires have not been ahem, chewed on by mice ;-)

Also, since wide plug gaps require a higher voltage to fire them, this will increase the chances of the Corona Effect. Usually more visible around the plug wires rather than the plugs. Note: not to be confused with the Corona "after effect" of excessive consumption of Coronas with limes.

[ Thanks to Greg Rollin for this information. ]

Determining Accuracy of Harmonic Balancer Mark

On my old Olds engines I've had plenty of trouble with the rubber deteriating on the harmonic balancer. Then the outer ring starts sliding around, and the timing mark is meaningless. Eventually one came off and rested against the front timing cover

I check it by pulling the 1, 3, and 5 spark plugs. First bring piston 1 to the top, and the mark should be close to zero. This is not a very accurate indicator of actual crank position since piston speed is minimum here. So next I probe down 3 and 5, and adjust the crank so these 2 pistons are exactly THE SAME distance down. Since these pistons are at maximum speed (in opposite directions), this sets the crank more accurately at zero degrees

Replacing a damper with another the same age is not a long term fix. Dick Miller rebuilds these.

[ Thanks to Bruce Roe for this information. ]

Distributor, Crank, Cam Relationships

The distributor must turn once to feed every cylinder a spark for every complete cycle. A complete cycle is by definition 4 strokes, or two turns of the crank. Therefore, dist'r speed = cam speed = 1/2 crank speed. And, turning the dist'r by say 2° alters timing by *4* crank degrees.

For an engine turning 1000 RPM at the crank, the cam is turning 500 RPM, and the distributor is also turning 500 RPM.

Given a firing order of 18436572 then I'd say that #8's throw will be 90° behind, or CCW of the #1 crankppin. #4 will be 180° CCW [not that that matters for 180...], etc. As viewed from the front of the engine.

[ Thanks to Chris Witt, Al Varhus for this information. ]

Distributor Shaft Play

Careful with this tolerance. Up and down movement is normal, but unfortunately, too much can cause problems. Since the distributor drive gears are helically cut, up and down play in the distributor shaft can lead to timing changes as the distributor driven gear moves up and down relative to the cam gear. Mr. Gasket and others sell shim kits which allow you to take out most of this unwanted motion. These are simply precision ground washers of various thicknesses which go between the distributor gear and the housing to take out the end play. Just drive out the split pin holding the gear to the shaft, place the shims over the end of the shaft, and reinstall the gear and retaining pin.

[ Thanks to Joe Padavano for this information. ]

Ignition Advance

The reason for ignition advance is that the air/fuel mix doesn't burn instantaneously - it takes a little bit of time from the moment the spark is set off to the moment when peak cylinder pressure is reached. During that time, the crankshaft keeps rotating. So if you lit off the mix at TDC, the piston will be well down the bore by the time peak cylinder pressure is reached, and you'll get lousy horsepower and lots of unburned fuel out the tailpipe. The cure is to light off the air/fuel mix *before* the piston reaches TDC, so that the peak cylinder pressure is achieved at just about the time the piston is positioned to take full advantage of it. This is what we call ignition advance.

Okay, let's back up a bit. Why do we need any ignition timing advance at all? Why not light the fire off when the piston is at TDC? The answer is that it takes the flame some time to grow to fill the whole combustion chamber, and during the time the flame is growing, the piston keeps moving. The only way to get the flame to finish burning and produce lots of pressure on the piston when it's ready to be pushed down the bore, is to light it off early, while the piston is still moving up the bore. That is why ignition timing is needed.

How much advance do you need? Clearly, it depends on how fast the air/fuel mix burns, and how fast your engine is turning. Roughly speaking, if your engine is turning faster, you want more advance; this is the why distributors have mechanical advance in them, which puts out the spark earlier and earlier in the cycle as the engine rpm's climb. Once you reach a high enough rpm, the air-fuel mixture begins to whoosh into the cylinder with so much velocity that it becomes turbulent, and consequently the flame spreads very fast; increase the rpm, and the mixture becomes more turbulent in direct proportion, and the flame spreads even faster. This means that once you exceed a certain high rpm, the mixture tends to burn in about the same number of crankshaft degrees, no matter what the rpm. Now you no longer need the ignition timing to keep advancing with increasing rpm, so the distributor is designed to level off the advance above some rpm.

The somewhat large overall advance numbers seem too large to believe, and it freaked me out also. However, when I began to understand the role of ignition timing, I began to understand why this much timing is okay in certain cases.

Your distributor contains a mechanism (mechanical/centrifigal advance) of springs and weights that advances the spark timing as engine rpm goes up. This is to compensate for the fact that the engine turns faster, so it goes through more degrees of rotation in the time the flame spreads through the chamber. To compensate the flame is lit off earlier.

The distributor also contains a vacuum advance canister. It's role is to add a bit of advance during certain high vacuum phases of driving, like cruise, mainly for fuel economy.

The reason for vacuum advance is that the rate at which the air/fuel mix burns also depends on how much of it is packed into the cylinder in the first place - i.e., how dense the mix is. When the engine is driving around at part-throttle, the almost-closed carburetor throttle blades restrict the amount of air/fuel mix entering the engine (compared to wide open throttle). This low-density mixture burns more slowly. To compensate, the ignition needs to be fired off earlier when the engine is at part throttle (than when it is at full throttle). The clever solution is vacuum advance. When the engine is at part throttle, manifold vacuum is high, and this sucks on the vacuum advance diaphragm and advances the spark. If everything is set up correctly, the extra advance compensates for the slower-burning mixture.

Vacuum advance during WOT acceleration is a common myth. More than one mechanic has told me this one. Part throttle yes, but not all out acceleration.

When the engine is at part-throttle (cruising at constant speed on level road, for instance), the intake manifold vacuum is high and engine load is low. That is to say, the resulting air/fuel mix is lean. And it turns out the speed at which a flame spreads in an air/fuel mix decreases when the air/fuel mix is thin. So the flame takes longer to spread from the spark-plug and fill the whole combustion chamber. If we want the combustion process timed right, then, we need more ignition advance at part throttle, to compensate for the slower flame burn in the leaner air/fuel mix. And this is exactly what the vacuum advance does: the vacuum cannister measures engine vacuum, which is to say, it measures engine load. The lesser the engine load or need, the more the spark gets advanced. Exactly what the engine wants, and a very clever idea!

During acceleration, there is less vacuum signal. Vacuum advance is less when there is less vacuum, using either manifold or ported sources, as I explained above.

Most vacuum advance units are not adjustable - the factory figures out what works to meet emissions requirements, then presets that amount in the vacuum cannister design. Some Mopar units are adjustable from the factory. For Fords and GM cars you can buy aftermarket adjustable vac. advance units (Accel, Crane, etc).

VACUUM ADVANCE: If you didn't disconnect the vacuum advance when setting the timing, it is probably bumping up your advance as you hit third gear, since your vacuum starts to come up as you approach top speed. It dials in greater ignition advance, which is necessary when you've got a thin or lean air-fuel mixture such as at part-throttle; you have to start that mixture burning quite early in order to get all that fuel combusted by the time the piston is passing TDC. It greatly improves part-throttle fuel-economy. You can disable it temporarily with a golf-tee plugging the line to the canister. It also bumps your idle speed up. That's it. Makes little to no difference for actual driving, only for idle emissions quality. Bob Barry

The total amount of advance or overall advance depends on many things (compression ratio, head design, rear-end ratio, weight of your car, etc) but I've been told numbers of around 10° to 15° advance at idle, around 36° full mechanical advance (with the vacuum advance disconnected). At part throttle, high rpm, with vacuum advance, the ignition timing should be somewhere in the range of 50°. That number surprises many, but that's what's needed for maximum fuel economy at part throttle (cruising).

Total advance at high rpm and wide open throttle = initial timing + mechanical advance

Total advance at high rpm and part-throttle = initial timing + mechanical advance + vacuum advance

One rule supercedes everything else: if the engine detonates, reduce the timing immediately till all traces of detonation are gone. Detonation will kill your engine in a very short time (it breaks piston rings, crumbles pistons, etc.).

The best way to set ignition timing is to modify the initial advance and advance curve to get the best power at WOT at all rpms. Do this with the vacuum advance disconnected. Once the mechanical advance is dialed in, connect the vacuum advance, and dial it in for best *part-throttle* power with no pinging or surging. This last step is universally omitted when the car magazines write about engine buildups.

A 2.56:1 rear is a pretty darn stiff rear ratio, which means the engine sees a much bigger load (less torque multiplication through the rear gear). A bigger engine load means increased cylinder pressure and increased tendency to detonate. Translation: be cautious in going to lighter and lighter distributor springs, as your engine is working harder than most due to the very stiff rear end. Again what I've heard for Mopars is to use full advance by roughly 2500 - 3000 rpm.

If you can get away with full advance at lower rpm with no pinging, fine. Just be very careful not to run into even mild "silent detonation" which can still break piston rings and damage pistons without being loud enough for you to hear over the sound of the car. Once you find the point where the thing pings, back off a few degrees to give it a safety margin. Also a hotter day or a tank of bad gas might come your way and needs a safety cushion. Better an engine a few % down on torque than one that needs a rebuild due to detonation.

Race engines don't need vacuum advance, because they're never at part-throttle anyway. Any street engine spends more time at part-throttle than WOT, and can always benefit from having vacuum advance. Magazines like Hot Rod test engines at WOT (Wide Open Throttle) on a dyno, where vacuum advance plays no role, so they leave it off the engines. Then they tell you that you need 36 deg, or 32 deg, or whatever, of mechanical advance. They totally fail to inform you that your engine will run better on the street with additional vacuum advance over and beyond that 36° or whatever.

See the Tuning section for how-to details.

[ Thanks to John Carri, others for this information. ]


You have to reduce ignition timing; the only question is where, and by how much. If it pings only under part-throttle, you can use an adjustable vacuum advance unit to reduce the timing provided by the vacuum-advance. If it pings under all wide-open throttle, you can back off total mechanical advance by reducing base ignition timing. If it only pings at certain rpms at wide-open throttle, you can use heavier springs on the advance weights to reduce the rate at which the mechanical advance comes into play.

You might also have to change the jetting to compensate for the vastly-different gasoline formulations available today.

[ Thanks to Bob Barry for this information. ]

Spark Quality

Does a "hotter" spark realy create a faster burn?

"Hotter" isn't what you think. High energy ignitions allow the plug gap to be increased, and also make "fatter" sparks. More spark surface area exposed to the mixture makes for more complete combustion. The other main performance item is the *duration* of the spark. Longer is better. Making a long duration spark has practical engineering limitations. MSD found the same results can be achieved with multiple short duration sparks. Getting the chemical reaction started is the big deal. Once it has started it will go as fast as it can react.

I don't believe they spark during the exhaust cycle, like some distributor- less (DIS) ignitions.

Funky stuff happens during the first few microseconds of ignition. It's a complicated thing. The flame can actually "blow" itself out under certain conditions, and reignite an instant later. Power lost. "Hot" spark helps a good deal.

[ Thanks to Dave Cullen for this information. ]

Oldsmobile Distributors

Date Code

You should find a 3 digit alphanumeric code which is the date-code (date of manufacture) of the distributor. An example would be 1A7 where the 1= Year (1971) and the A= Month (Jan.) and the 7=day of the month (7th). If it is the original distributor, this code should correspond somewhere near the date your car was manufactured. GM did not use I's in these codes because of confusion between 1's. Otherwise M would be the 13th month which does not exist, and again 7 being the 7th day of the month.

[ Thanks to Kevin Hoopingarner, Chris Witt for this information. ]

Olds Distributor Specifications 1965-1975

Note that factory vacuum advance canisters generally are stamped with the last 3 digits of the part# and the total vacuum advance it makes, in degrees. E.g., the first 1965 unit shown should be stamped "210 16" if it provides 16° of vacuum advance.

Dist #   Vac Unit  Applications
1110322  1116210   All 33xx, 35xx series [Cutlass]
1111029  1116232   34xx-36xx all, 3855, 3865, 52xx w/L65 [L65= 330 LC]
1111048  1116232   3827, 3837, 3867, 52xx exc. L65, all L74 & L76
                   [U500003G, T500003G engine ID's 330-4V 10.25 CR]
1111042  1116232   54-86, 34, 36, 38xx w/L77 or L78
1111089  1116232   56-58 w/L65

1111048  1116232   330 HC & L74, L76
1111048 [specs: VA begin 6-8 inHg, 9 deg @15.5-19.5 inHg.
                   Mech 0-2 @400RPM, 7.7-9.7 @1025, 14-16 @2000]
1111029  1116232   330 LC
1111042  1116232   400/425-2V HC
1111151  1115361   425-4V HC
1111151 [specs: VA begin 8-10 inHg, 9 deg @16.5-18.5 inHg.
                   Mech 0-2 @600RPM, 3.5-5.5 @900, 8-10 @2100]
1111089  1116232   425 LC

-1967-   *= UHV or Capacitive Discharge Ignition System
1111048  1116232   330 HC & L74, L76
1111029  1116232   330 LC
1111042  1116232   400/425-2V HC
1111188  1116232   UHV dist'r for 400/425-2V HC
1111151  1115361   425-4V HC
1111179  1115361   UHV dist'r for 400/425-2V HC
1111089  1116232   425 LC
1111189  1116232   UHV dist for 425 LC

-1968-   *K66=  UHV or Capacitive Discharge Ignition System
1111286  1973406   350 LC
1111299  1115361   350 HC
1111466  1973407   400 LC
1111287  1973408   400 HC MT exc. W30
1111290  1973408   400 HC MT exc. W30, w/UHV
1111290 [specs: VA begin @8-10 inHg, 12 deg @18.5-20.5 inHg.
                   Mech 0.4-2.4 @500RPM, 8-10 @900, 10-12 @2000]
1111468  1973418   400 HC AT & all W30
1111468 [specs: VA begin @10-12 inHg, 8 deg @16-18 inHg.
                   Mech 0.5-2.5 @450RPM, 7-9 @1000, 9-11 @1900]
1111470  1973418   400 HC AT & all W30, w/UHV
1111288  1973407   455 LC
1111291  1973407   455 LC, w/UHV
1111289  1973408   455 HC exc. W34; also H/O with A/C
1111292  1973408   455 HC exc. W34, w/UHV
1111469  1973408   455 HC w/W34
1111471  1973408   455 HC w/W34, w/UHV

-1969-  *No K66 [UHV ignition system] listed in CSM
1111961  1973408   350 LC
1111930  1115361   350 HC
1111933  1973418   400 HC AT & all W30
1111933 [specs: VA begin @10-12 inHg, 8 deg @16-18 inHg.
                   Mech 0.5-2.5 @450RPM, 7-9 @1000, 9-11 @1900]
1111932  1973408   400 HC MT exc. W30
1111932 [specs: VA begin @8-10 inHg, 12 deg @18.5-20.5 inHg.
                   Mech [email protected] 500RPM, 8-10 @900, [email protected] 2000]
1111934  1973407   455 LC
1111935  1973408   455 HC exc. W34
1111936  1973408   455 HC w/ W34
1111936 [specs: VA begin @8-10 inHg, 12 deg @18.5-20.5 inHg.
                   Mech [email protected], 5-7 @1000, [email protected]]

-1970-        *No K66 [UHV ignition system] listed in CSM
1111975    1115361   350-4V A-body AT, AT w/AC, MT, AT or MT w/W31.
1111976    1973408   350-2V A-body AT, AT w/AC, MT [engines QA,QJ,QI]
1111976    1973408   350-2V B-body AT, AT w/AC, MT [engines TD,TC,TL]
1111981 *1 1973427   455-2V-HC A-body [TX,TY]
1111982    1973427   455-4V-HC A-body [TW,TV,TU]
1111979    1973427   455-4V-HC A-body AT w/W30 [TT]
1111979 [specs: VA begin @10-13 inHg, 4.2-7.3 deg @16 inHg.
                     Mech 0-3.5 @375RPM, 7- 10.3 @575, 14-16 @1500]
1111977    1973427   455-4V-HC A-body MT w/W30 [TS]
1111977 [specs: VA begin @10-13 inHg, 4.2-7.3 deg @16 inHg.
                     Mech [email protected] 500RPM, 8-10 @900, 10-12 @2000]
1111981 *1 1973427   455-4V-HC Vista Cruiser AT [TQ,TP]
1111980    1973408   455-2V-HC B&C-body (88 & 98) [UC,UD,UJ]
1111981 *1 1973427   455-4V-HC AT B&C-body (88 & 98) [UN,UO]
1111982    1973427   455-4V-HC AT B&C-body (88 & 98) Police W-33 engine [UL]
1111981 *1 1973427   455-4V-HC AT E-body (Toronado) [US,UT]
1111982    1973427   455-4V-HC AT E-body (Toronado) w/W34 [UV,UW]
1111978 *2 1973430   All where 1111981 is used above
*1= 1st type, *2= 2nd type

1112079  1973407   350 A-body  [tune-up label OA,OB]
1112085  1973407   350-4V A-body  [tune-up label OB]
1112079  1973407   350-2V B-body [tune-up label OA]
1112033  1973408   455 A-body [tune-up label OD,OF,OG,OK]
1112036  1973407   455 A-body [tune-up label OE]
1112034  1973407   455 A-body [tune-up label OE,OL]
1112033  1973408   455 B&C-body [tune-up label OF,OG,OJ]
1112078  1973408   455 E-body (Torondo) [Engine US,UT] [tune-up label OH]

1112106  1973407   350-2V [code QA,QB,QC,QN]; 350-4V-MT [QD,QE]
1112085  1973407   350-4V-AT [QJ,QK,QP]
1112033  1973408   350-4V exc. MT/W30/Toronado [UA,UB,US,UT]
1112034  1973407   455-AT-w/W30 [UL,UN.UO]
1112036  1973407   455-MT-w/W30 [UL,UN.UO]
1112036 [specs: VA begin @6-8 inHg, 13 deg @16-17.5 inHg.
                   Mech 0.4-2.4 @500RPM, 8-10 @900, 10-12 @2000]
1112172  1973408   455-4V-AT Toro & MT [UD,UE,UU,UV]
1112033  1973408   455-4V-MT [UD,UE,UU,UV]

1112226  1973468   350-2V L-32 & L-33; Omega, Cutlass [code QP,QQ,QS,QT];
                   "88" [code QN,QO]
1112195  1973453   350-4V L-34 AT (exc. wagon)
                   Omega, Cutlass [code QA,QB,QJ,QK]
1112225  1973453   350-4V L-34 AT wagon Vista Cruiser [code QU,QV]
1112222  1973453   350-4V L-34 MT Omega, Cutlass, V.C. [code QC,QD,QE,QL]
1112197  1973232   455-4V L-75 MT Cutlass [engine UD]
1112197  1973232   455-4V L-74 & L-75 AT Cutlass, 88, 98 [engines UA,UB,US,UT]
1112198  1973466   455-4V-AT L-78 AT Toronado [engines UU,UV]

1112195  1973453   350-4V L-34 AT (exc. wagon)
                   Omega, Cutlass [code QB,QC,QL,QO]
1112226 *1  1973468  350-4V (Calif.) L-34 AT (exc. wagon)
                   Omega, Cutlass [code TB,TC,TL,TO]
1112828 *1  1973468  350-4V (Calif.) L-34 AT (exc. wagon)
                   Omega, Cutlass [code TB,TC,TL,TO]
1112550  1973427   455-4V L-76 [UV,UX] Cutlass
1112225  1973453   350-4V L-35 [code QU,QW] "88" cars;
                   L-34 wagon AT [QU,QW] Cutlass, V.C.
1112197  1116232   455-4V (Calif.) L-74 &L-75 AT [UA,UC,UL]
                   Cutlass, wagons, 88, 98.
1112531  1973496   455-4V (Calif.) L-74 &L-75 AT [VA,VC,VL]
                   Cutlass, wagons, 88, 98.
1112506  1973474   455-4V w/K-86 L-74 [UB,UD,UN] 88 & 98
1112532  1973499   455-4V w/K-86 (Calif.) L-74 [VB,VD] 88 & 98
1112827  1973497   455-4V-AT L-78 [UO] Toronado
1112825  1973496   455-4V-AT (Calif.) L-78 [VO] Toronado
1112830  1973500   455-4V-AT w/K-86 L-78 [UP] Toronado
1112829  1973499   455-4V-AT w/K-86 (Calif.) L-78 [VP] Toronado
1112172 *2  1973408  455-4V L-78 [VS] Ambulance, Hearse; [VV,VT] Motor Home
1112082 *2  1973408  455-4V L-78 [VS] Ambulance, Hearse; [VV,VT] Motor Home
417923   -none-    455-4V-LC [BA] Marine
417961   -none-    455-4V-HC [BC] Marine
1112228  1973430   455-4V [CE] Irrigation motor
NOTES: *1) 1112226 = 1112828; *2) 1112172 = 1112082.

-1975-  including 400 Pontiac motor info but not 231 V6 or 250 I6.
1112951  1973556   260-2V (Calif.) LV8 AT (Calif.)
                   [code TE,TJ,TP,TT] Omega, Cutlass
1112956  -none-    260-2V (Calif.) LV8 AT (Calif.) [code TE,TJ,TP,TT]
                   Omega, Cutlass
1112896  1973525   Omega 350-2V L-32  (exc. Calif.) [RS,RT];
                   350-4V L-77 AT (exc. Calif.) [RW,RX];
                   350-4V L-77 AT (Calif.) [PA,PP]
1112936  1973531   350-4V (Calif.) L-34 AT
                   [code QL,QO,QX,QU,Q2,Q3,Q4,Q5] Cutlass, 88.
1112953  1973536   350-4V (Calif.) L-34 AT [code TL,TO,TX,TU,TW,TY] Cutlass, 88.
1112500  1116493   400-2V L-65 AT (exc. Calif.) [YH,YJ] 88 exc. Wgn.
1112928  1973493   400-4V L-48 AT (exc. Calif.) [YM,YT]
                   (YM= early prod.) 88 Wgns, 98.
1112958  1973514   400-4V L-48 AT (exc. Calif.) [YL] (late prod.)
                   88 Wgns, 98 sedans.
1112937  1973563   455-4V L-74 AT (exc. Calif.) [UB,UC,UD,UE] &
                   (Calif.) [VB,VC,VD, VE] Cutlass, 88, 98.
1112952  1973563   455-4V-AT L-78 [UP,U2] Toronado (exc Calif)
                   or [VP] (Calif.)
1112893  1973523   455-4V-AT L-78 [RA,RC] (exc. Calif.) Motor Homes
1112945  1973560   455-4V-AT L-78 [RB] (Calif.) Motor Homes
417961   -none-    455-4V-HC [ML] Marine
418482   -none-    455-4V-LC [MK] Marine
550360   -none-    350-4V-LC [engine MJ] Marine
1112228  1973430   455-4V [CE] Irrigation motor
[ Thanks to Chris Witt for this information. ]

Distributor End Play

Please be aware that the instructions on shimming the distributor shaft for minimal endplay are *wrong* when it comes to Oldsmobile distributors. Carl Dudash, who used to be on this list, pointed this out about a year ago. I'll paraphrase his original explanation:

Chevy distributors turn clockwise, seen from above; consequently the distributor shaft is pushed up, out of the engine block, by the angled cam gear when the engine is running. To prevent exceeding the maximum air-gap the Pertronix module can tolerate, Chevy distributors have to be shimmed.

Olds distributors turn anti-clockwise, and are pulled downwards, into the engine block, when the engine is running. The end of the distributor shaft is actually pulled down into contact with an internal thrust surface in the block. For this design to work, the distributor *needs to have* some endplay; shim it and you'll eat up the shims and may damage the distributor too. To set up the Pertronix module in an Olds distributor, push down on the distributor shaft so it bottoms out in the distributor housing, then set the airgap.

As another listee pointed out, Pertronix now has a better designed system which no longer uses the cheesy warped plastic magnet ring, but instead triggers off the cam that used to operate the points formerly. This system is not sensitive to distributor shaft endplay, and is a much more elegant solution IMHO.

[ Thanks to Carl Dudash, John Carri for this information. ]

Ignition Types

Mechanical vs Solid State

It depends on if it is a mechanical or electronic (also called "solid-state") regulator. While heat is definitely bad for all electrical devices, whether mechanical or not, the firewall above the distributor is usually cool enough.

A mechanical voltage regulator is just that -- mechanical. It consists of a couple of relays, a couple of resistors, and (in some regulators) a diode. In the mechanical regulator the armature is a flexible, spring metal arm with contact points on the end. Like ignition breaker points, these points can arc, corrode, pit, and accumulate deposits. Also, with the constant flexing of the armature (many times a second), the relays may get to a point where the armature no longer actuates properly. Also, the resistors are the wire-wound type and may eventually burn through, or lose their resistive tolerances, though that last item is unlikely. So, in a mechanical regulator failure is often due to mechanical failure or similar mechanical problem, like burned or corroded contact points.

An electronic regulator accomplishes regulation by means of semiconductor devices (transistors, diodes, etc.). No mechanical action exists. As such, they can be made smaller than their mechanical counterparts. Hence, it's just convenient to install it in the same case as the alternator. However, some manufacturers (Ford and Chrysler) initially just replaced their external mechanical regulators with external electronic versions and made little change to the alternator itself.

Failure in an electronic regulator can be due to heat. Severe short circuits can also damage them. Then there's entropy. That is, everything decays. The constant voltage handling can just eventual wear the electronics out, in the same way an electronic ignition module just goes bad or gets flaky. The transistors can eventually short or open. However, electronic regulators do a superior job of voltage regulation and ensure a far more stable power supply than any mechanical regulator could accomplish. That's why they're preferred for HEI.

[ Thanks to Thomas Smith for this information. ]


The points are just a mechanical switch. The cam in the distributor pushes open the points and spark happens. In an electronic ignition, a solid state device takes the place of the points. No wear, no adjustments required. And because of certain electrical advantages (I'll spare everyone the techno-babble), electronic ignitions make a higher voltage spark and perform far better at high rpm's than points ignitions.

You need about 15,000 volts to fire a plug with a .035 gap. Higher compression in the cylinder requires even more. Larger plug gap requires still more. A larger gap means a longer spark, which helps combustion effieciency by providing ignition to a bigger area of mixture in the combustion chamber. This will help mileage, emissions, and power. The GM HEI units provide about 30,000 volts. Bzzzzt.

When the points open, the condenser is there to PREVENT the spark from continuing to jump the points gap by absorbing the surge of current that results from the points opening. In fact, if the system worked as you describe the ignition system would work very poorly, if at all. You may note that electronic ignition systems do not require a capacitor as this problem of current continuing to flow across the points gap does not exist there. The circuit interruption is quick and complete. Capacitors in electronic ignition systems work to prevent radio interference only.

The way the system works is this. With the points closed, current flows through the primary side of the coil to ground. The current level in the primary side is being brought to that allowed by the entire circuit. This takes time. As the current flows through the coil, it creates a magnetic field which is concentrated by it's iron core. When the points open, the magnetic field collapses in the primary which increases it's level to hundreds of volts. That's right. Hundreds of volts will be felt by both windings. A mere 12 volts is not simply stepped up to the thousands required for a spark. It first builds to hundreds as the magnetic field in the primary side collapses. This voltage level is stepped-up by the secondary windings to thousands of volts. It is this voltage which fires the plug. Electrically, it's e = L di/dt, or voltage = the coil inductance times the rate of change of primary current as the stored coil current discharges. Calculus in yer Oldsmobile.

Now, if the condenser provided the energy for the secondary coil windings, it would actually oppose, thus slowing, the magnetic collapse in the primary winding as it would allow current to continue flowing across the points, when complete stoppage is the goal. This would create a very poor spark. Besides getting virtually no spark, a missing or open condenser (capacitor) will cause the points to burn out very quickly. Just take that as FYI. However, for optimum performance, the collapse of the magnetic field int he primary side must be as rapid and complete as possible. Any sparking across the points gap slows and reduces the completeness of the collapse. The condenser stores most of the current that attempts to continue across the gap.

Note a few crucial facts. First, an ignition coil is simply an iron-core, step-up autotransformer. Nothing more. Nothing less. As such, transformers DO NOT work with direct current. The only reason they work in a car's ignition system is that the breaker points (or electronic ignition module) constantly and rapidly makes and breaks the circuit creating a quasi-AC current. When the discharge (spark) begins, the coil secondary inductance and distributed capacitance becomes a tuned circuit, and resonates at some natural frequency. If you ever looked at a spark with an oscilloscope, you'll see that it is in fact a high frequency ac signal. That's why it can interfere with radio. In fact, at 600 rpm, the frequency of the ignition circuit in a V8 engine is 40 Hertz. In fact, it is this making and breaking of the circuit which causes the primary current to be induced into the secondary.

Second, since an A C-type of signal is felt by the points, this is precisely the reason the capacitor (the real word for condenser) works. Capacitors act simply as open circuits to direct current, but they act as shorts to AC. So, the instant the points open the change in current acts as AC and the surge is stored by the capacitor. The charge stored by the capacitor is not released until the points close again.

[ Thanks to Thomas Smith, Dave Cullen for this information. ]

"Dwell" is the amount of time, as measured in degrees of rotation, that the primary circuit of the ignition system is closed, allowing the ignition coil to build a charge. In short, the higher the dwell, the longer the coil has to charge. However, there are only 360° in a circle, so the more time you give the coil to charge (higher dwell) the less time you allow for the coil to discharge, firing the spark plug. The goal is to find the ideal balance between the two.

Bear in mind, once an inductive circuit (i.e., ignition coil) has built to its maximum charge, any more time allowed for charging is unnecessary and is a waste. So, if only 30° of dwell are required to charge the coil, allowing 38 degrees only results in 8° of wasted time that could be used on coil discharge, hence, spark plug firing.

On the other hand, allowing too little dwell results in insufficient coil charging which produces a weak spark.

Both spark power (wattage: voltage X amperage) AND spark duration are necessary to promote complete combustion and efficiency. So, you need enough dwell to provide sufficient spark power but not so much that you have insufficient spark duration.

The points distributor will have a metal "door" which slides up and down (normally down to close) so you can set the dwell for the points. The points are normally closed to produce a field in the ignition coil. When the points open, the field collapses. The energy of the collapsing field is used to fire the plug. You need to have the points closed long enough to produce a field in the coil.

Anywhere between .016 and .018 is correct for a starting point. This will get the car started. Once that's done, the points should be readjusted using a dwell meter as the car is running.

I had instructions years ago for easy setting of dwell:
Start with "about" 0.020" gap. Start motor. Turn points adjusting screw CW until engine begins to misfire. Back out 1/2 turn.

I did this, then checked with dwell memter; it was right on the money. Optimal is 30°, acceptable range is +/- 2 degees.

Be sure to set dwell, THEN timing, as changes in dewll change the timing... because the spark occurs when the points open. Change when they open [the dwell], you change the spark time.

[ Thanks to Dan Lacey, Thomas Smith, Chris Witt for this information. ]

Points for Performance:
First buy a recurve kit. Put the weights on and one light spring and one medium spring. Next set timing at 10° to 12°. Next you need to check total timing at 1800rpm's. Oldsmobiles like 36° for this. Next replace the stock points with Standard Ignition Performance Points. It has a heavier spring to stop floating of the points. I check my plugs a couple times a year to check for fouling out or if the electrode is wearing down. For your car, it depends on how much mileage you put on the car. Check the rotor and cap once a year for carbon tracks or burnt up tips. Wires replace when you feel the wires are old and brittle. A good indicator is when the cap is trashed, so are the wires.

[ Thanks to Mark Prince for this information. ]

High Energy Ignition (HEI)

HEI is a big distributor that sits on the back of 1974 and later oldsmobiles. The caps and rotors are noticeably bigger than points type distributors. For reference compare the 1974 and up with the late 60s and you'll see the height and diameter size difference in the units. Another way to tell is that the points type distribs have the coil mounted separately on the intake manifold, whereas in the HEI it sits on top of the cap. Both are black if the caps are factory.

The HEI (high energy ignition), was standard on GM cars from about '75 up till the change to fuel injection. Avoid the '81 up unless you have a computer in the car. The distributor itself it pretty distinct. It's larger in diameter than the points type, and the coil (about 3", cubical, but usually covered by a plastic cover) is incorporated into the distributor cap. They also came with a plastic "ring" that snaps on top of the distributor that holds down the wires and has the firing order written on it, although these rings are frequently gone. On the lower side (usually driver's side) of the distributor cap are spade connectors for the ignition, ground, and tach.

If you really want to be sure you can ID an HEI distributor, go to the local parts store and look at the HEI distributor caps. They're certain to have dozens of them out on the racks.

Reasons to use an HEI: First, the performance of a brand new points system vs a new HEI may appear to be identical, but they are not. Some partial misfires will occur, and any extremes such as temperature, gas mixture variations, idle or max RPM, or less than perfect engine breathing will increase these. I realize some will they can't feel any difference, but I have found some "can't feel" differences may be quite obvious on a stopwatch. By putting more energy into a wider spark gap, the HEI minimizes these effects. A good aftermarket booster (I use Jacobs) will do even better

Second, the whole points system is marginal, and new parts start degrading almost immediately. The cap and wiring are only up to the job when new and dry; remember the wet ignitions, the sparks across a frosty cap and less than new wires? For that reason an ignition booster may not do much good under extreme conditions. The points ability to deliver maximum energy will start degrading as soon as you drive it out of the garage; my high compression 63 Cutlass would be quite noticable after a few thousand miles. Wear on the block can shift timing. The HEI system has enough margin built it to deal much better with extremes, even with a booster. And instead of constantly deteriorating, the HEI maintains a consistent superior level of performance for a very long time

Third, maintenance. Since the HEI isn't stressed to the limit, there isn't a constant need to change cap, wires, and plugs. And no points! I prefer to sandblast and regap plugs at 15,000 mi, replace at 30, still a huge improvement

Fourth, simplicity. I always found the separate distributor, coil, and ballast with low and high tension wires connecting things pretty annoying. The HEI is a single unit with a single 12V wire. When troubleshooting, the whole system (except plugs) can be popped out in a few minutes and another dropped in

[ Thanks to Chris Fair, Tom Lentz, Bruce Roe for this information. ]

GM MISAR HEI Variation

I remember the 1977-78 ignition system on the Toros was called MISAR. They are a bit of a strange HEI. The vacuum advance is replaced by an early computer with a lot of extra wiring and sensors. I actually transferred one of these complete 78 Toro systems to my Delta 88 with the 403 engine. Later I found a simple 79 Toro HEI had exactly the same performance, so I switched to that

There is a standard way of putting in HEI so that connections line up, and there is room for some timing adjustment. However in theory there are a multitude of ways of putting it in a non-fuel injected engine that will work. The critical thing is that the rotator points to the correct wire at the correct time. The gear has 19 teeth, so there are 19 ways to insert the shaft. Sometimes things hit when the HEI is rotated to set timing, so I just pull the whole thing, rotate everything 1/19 in the direction to give more room, and set timing here

For any orientation of the HEI rotator, there are 8 possible positions for the body (for a V-8). However the plug wires must maintain a fixed relation to the rotor, so they would be moved from hole to hole on the cap. The cap is keyed to only go on the base one way.

[ Thanks to Bruce Roe for this information. ]

GM Capacitance Discharge

In 1967 Oldsmobile introduced a Capacitor Discharge ignition system. Option code K66. This was available on the 400 (including W-30) and 425 engines. Although I do not believe this was a factory option on the 330's, it certainly could have been added by the dealer or installed with over the counter factory parts. The UHV, (Ultra High Voltage) system is an early electronic ignition. These utilized a magnetic pickup, which was triggered in a similar manor as an HEI. Although they were (are) a reliable system, it was not a particularly popular option. (Perhaps people preferred points/cond. over this new fangled electronic stuff). It was discontinued in 1968.

This system first available in 1967. This truly was the forerunner of HEI, using the same magnetic pickup in a standard small (points-style) Delco distributor. The electronic control module was an MSD-sized unit mounted to the inner fender, while the coil looks like a standard Delco external "points-style" coil, however it is different internally and painted red instead of black. I think UHV was available at least through 1969.

If you are planning on purchasing the setup, be sure to get all of the pieces. As some individual components are getting somewhat hard to find (read $$$). This includes the special red coil. A similar system was used on late 60's Corvettes. And was more popular with the Vette buyers. Consequently, some of the distributors internal components are available through suppliers of Corvette parts. Although Olds used a different amplifier than the Corvette, they can be repaired by anyone who does the Vette repairs. Spark plug gap was increased to .045 with the UHV system.

[ Thanks to Greg Rollin for this information. ]


The benefits of high performance aftermarket ignitions in stock, low compression setups can vary. Sometimes the benefits are negligible. For instance, a book I have on electronic ignitions indicates that stock low compression setups often only demand 6,000-8,000 volts from a coil, regardless of it's advertised output. In fact, advertised output is just that -- ADVERTISED. It is a rating that is usually only realized in a lab. I have that on the word of a tech at MSD, itself.

However, hipo ignitions can provide the extra punch necessary to fire high performance, high compression, dense mixtures. One thing they all have in common is electronics. Some are analog, some are digital. However, the precision offered by the electronics produces much cleaner current switching -- allowing greater coil efficiency, and much more precise timing than could ever be achieved with points. So, I think such systems are often a good idea in replacing points, even in a stock installation. Their benefit over a stock GM HEI is much less significant than points, however. Many folks insist, though, that they noticed an improvement when they hooked an MSD up to an HEI.

What they do varies with design. Some increase spark duration for a more complete burn. Some, like the MSD fire multiple sparks (actually, MSD is an acronymn for Multiple Spark Discharge). Most advertise at least some increase in spark current, which will produce a higher wattage spark making for a hotter, fatter spark. One of their main benefits, especially when compared to points, is more consistency against misfiring. Many also incorporate rev controls and adjustable timing.

My guess is that if you already have an HEI, just the MSD would be all you should need to add. Installing a remote mount coil (to keep it cool) and using a higher output coil, if you're running high compression would also be helpful.

[ Thanks to Thomas Smith for this information. ]

Upgrade Cautions:
One point seems to be getting lost in some of the responses tho. There is no way that Mallory, Pertronix or any other aftermarket mfr can come close to the development investment by GM and the experience of millions of systems installed. The only systems that can claim even a smidgen of that are those that have been out there for many, many years. And by aftermarket definitions, they are probably already obsolete and have certainly been "updated" based on the experiences of us, the people who paid money only to have them crap out. Ask me about the adjustable timing device by a big name supplier I bought some years ago. It was so good, as near as I can tell, it isn't offered anymore. When it failed, the backfires it caused cost me damn near the entire dual exhaust system on a motor home! Now that was an expensive R&D effort - for me! Not to mention that the episode scared the hell out of the wife who was afraid to even get back into the beast. These kinds of experiences I don't need.

If you store you prized classic Olds in a place where the points are going to deteriorate at such a rate that they become unreliable in a short time, you have much bigger problems to worry about than frequent tune ups! Points just are not that unreliable. They work quite well actually. Obsolete doesn't mean it doesn't work. Carburetors are obsolete too, but don't tell Holley, Carter, Edelbrock, etc.

If it was my car and I wanted stock appearance, and I drove the car any distances at all, I'd run points. Or buy, and carry at all times, a second version of the solid state gizmo I used to replace them. That's a pretty expensive alternative to points which are probably, admittedly IMO, more reliable than the gizmos.

I definitely do not like being stranded in the middle of nowhere with equipment that needs a well stocked specialty store, or for these items maybe a phone order catalog, to get the parts I need to get up and running again.

Kurt Heinrich has noted OAI systems can clear the HEI. A friend of ours has a 69 Cutlass (non OAI) with an HEI, his barely clears and he had to put a piece of heater hose between the HEI and air cleaner. It was arcing to ground. Now that's a SPARK! He shows his car at OCA National Meets and hasn't been dinged for the HEI yet - it can't be seen under that big air cleaner!)

If it was my ~70's OAI air cleaner and clearance was a problem, before I used a F*rd service tool on it I'd look at possibly using a non-OAI base, just for cruising. They fit, are easy to find and are cheap. Paid $5 for the last one I bought.

Since I run an Edelbrock Troker intake on my 67, there's no clearance problem with the HEI, like an inch and a half to spare! The problem is the OAI air cleaner interferring with the hood - which is what originally spawned the scoop you can see on the Bryceman's page. I wasn't about to give up my OAI shroud either!

The point of my comments were to point out the reliability of the HEI versus aftermarket stuff. I am a firm believer in doing what you like to your car. Neither of ours are offerings to the gods of correctness. Like I used to post at the end of my messages, "Enjoy The Ride!" (Too bad it wasn't a US mfr who coined that one.)

BTW, dual points used to be the "hot setup" way back when, and single point systems were "obsolete". WHAT A PAIN IN THE #$$% they were!

Here's something to think about with light sensing distributor set ups. If this is strictly a race car or show car that only goes out in nice weather. then thats fine. But if this is a daily driver, don't be suprised if on cool damp days the car runs poorly...or not at all. This is due to condensation refracting the light beam. Try diagnosing that one when it happens. Car starts...runs fine for the first few minutes then either starts missing or stops altogether. 10 min.s later repeats the cycle. Been there many moons ago with a 68 AMX....not fun.

Pertronix is one approach, also consider the MSD and similar Mallory systems. You can hide the control box, if you want. Since the points are only used to trigger the unit you've still solved a problem by cutiing the amperage across the points to darn near zilch. The current flow is what eventually kills a points set.

[ Thanks to Bob Handren, R. Kevin Noon for this information. ]


Also, for those of you who want to keep the stock look of a points-style distributor without the hassle points can be, check out the Stinger ignition system. It can be installed so that it's practically invisible, yet has the modern convenience of electronic ignition. Call Dave or Karen at Dave Smith Engineering (909) 371-7040.

I have used the Stinger system on both street and circle-track Olds engines with real good results. It could be hidden for that "untouched stock" look, since the trigger box (ignition control) is small. MSD ignition boxes will work with the Stinger-equipped distributor as well.

Dave Smith Engineering sells a kit that replaces the points with a magnetic trigger and a box to control the coil. Everything's bolt-in after you install the kit on the distributor. I had one on my race car in '92 and used one on the street until the distributor's bushings wore out. That's the only caution I'd post about it, be sure the distributor's bushings are in good shape before you install the kit. It uses the stock coil (most hi-perf coils will fry the box) and everything else that the points-type unit did, making it a low-cost alternative to points. Contact Dave Smith Engineering at (909) 371-7040 (Corona, CA).

[ Thanks to Ken Snyder for this information. ]


Just did this on Quincy's new 455. I used the PerTronix conversion. It came with two components. The trigger that replaces the points and a circle of magnets. The rebuilt engine came with a point distributor because an HEI wouldn't fit with this Offy intake. It's real simple to install.

Unscrew the points, and remove saving the screw. Now screw down the electronic trigger in place of the points. In my case there was a vacuum advance screw head in the way of the electronic trigger mounting bracket from mounting flat. I needed trim a notch in the trigger mounting bracket for the screw head to fit into. This did immediately void my warrantee but without cutting this notch, there was no way the trigger was going to mount flat. The screw head was part of the mounting structure for the vacuum advance system under the points plate and could not be removed or relocated.

You can run the triggers two wires through the distributor caps points adjusting window and out to the coil. You can also run the wire down through the distributor and out the hole the original points wire ran. This will probably require removing the distributor to do so I suggest for at first you run the wires through the cap metal window until you've run the electronics a bit. Make sure it's installed right and runs OK with the new components. The wires simply go to both the positive and negative posts on the coil.

Remove the rotor, and than the screws from the rotor. The ring of magnets slips over the mechanical advance weights and platform on top of the rotor shaft. Than screws up to the under side with screws supplied. these screws go up through the advance weights platform and through your rotor holding the whole assembly together. There is to be between .010 and .060 of clearance between the magnet ring and the trigger. The kit supplies spacer washers that you install above the magnet ring and the advance weight platform to drop the magnets closer to the trigger.

Use the original Positive electrical feed for the distributor. Use the original coil for the points system as if it required a ballast resistor it will probably already be on the positive feed for the coil. If you use a new coil you will need test it to see that it has 1.5 ohms of resistance. If not you will need buy a ballast resistor and install it. This is very important as without this resistance either within the coil wiring or via external resistor, the electronic trigger will burn out. You should be able to take your new coil to a Radio Shack to test for proper resistance. Most repair shops have an Ohm meter and can also test the coil.

Except for finding someone who could use an ohm meter, This was an extremely simple conversion. I've yet to pull the distributor to run the wires through the original points wire hole. The whole process didn't take 10 minutes. It sounds much more complicated that it is actually.

My PerTronix system cost just under $60. Personally I prefer it to the unilight as the unilight requires a beam of light that can be effected by moisture and heat. The magnet trigger system of the PerTronix doesn't have this problem. Not to mention that the Unilight system costs about 50% more than the PerTronix system.

There are two styles of the Pertronix for GM vehicles. The older style uses a magnet ring and the newer, easier style uses a lobe sensor. It seems as if you have the older, magnet ring style. Now, to your question:

The Pertronix instructions stating that you need to shim an Olds distributor are wrong.DO NOT shim an Olds distributor, you'll chew up the shims and maybe the distributor and/or cam gear too. Just push the shaft down lightly when you're setting the air-gap.

The advice to remove the distributor applies to engines, such as Chevrolet, which acutally force the distributor shaft up as it spins. This necessitates installation of some shims between the drive gear and the shaft housing to keep the shaft from riding up too high. However, you're in luck because you have (drum roll) an OLDSMOBILE! Since Oldsmobiles spin the distributor the opposite direction of Chevrolets, they pull the shaft down, usually negating the need for shims. So, the air gap won't change. You should be able to install the kit without removing the distributor, but it is easier if you do remove the distributor. You will, however, still need to make sure the air gap is okay.

Follow this link for more information: http://www.vintageperformance.com/retrorockets/gm.htm.

[ Thanks to Gary Couse, Thomas Smith, John Carri for this information. ]

Points to HEI Ignition Conversion


It is clearly superior (to me) for the following reasons
  1. Smoother idle.
  2. Better economy, slighly more power.
  3. Reliable so long as you stick with GM, not aftermarket, parts.
  4. Reliable so long as you keep an extra ignition module in the glove box.
  5. No points to adjust or dwell to scr*w with ever.
  6. Fun swap.
  7. Bolt in mechanically, though wiring changes are required.
  8. More modern. If the GM engineers had found points were better they would have stuck with 'em.

Cheap, it simplifies tuning, reduces radio noise, smooths the idle, and provides more consistent timing on the top end. No drawbacks except it costs $40 bucks or so in the junkyard and maybe $200 for a new one. Get the air cleaner assembly from an HEI engine as well, as the original air cleaner will hit the HEI distributor cap.

Simply put, in the old days (points) there was a resistor used to drop the current availble to the ignition during normal running conditions to prevent the points from burning out quickly. For starting, the resistor was bypassed so you could get a nice, "hot" spark for easy starting.

The HEI does not need this current reduction, and it can acutally be harmful to the HEI module if it is run thru the resistor. Therefor, the HEI needs just to be connected so that it receives a full 12 volts in either of its to states - running or starting.

You hit it right on the head (ouch!). The module in the bottom of the HEI does the same thing the points did in the old days, only now it's all electronic and unlike the points it's non-adjustable for dwell degrees. But you'd be hard-pressed to find someone who switched back to points after trying an HEI. The units do a fine job, even straight out of a salvage yard - did that on Grace when she was a street stock. You can run more plug gap, and in turn have less chance of plug fouling, even though I can never remember fouling out an Olds.

What we are doing on Grace now is using a computer-controlled HEI. These units don't have vacuum or mechanical advance, which we don't want on our circle track engines. The MSD system wires hook up directly to the pick up coil in the bottom of the housing, and route out to the ignition box (to give you an idea of how much more powerful MSD boxes are, remember that the red box takes the place of the module that's usually in the bottom of the housing), where it's processed to the coil (and tach) and then to an external coil. MSD also sells an adapter that allows you to attach that external coil through the HEI cap.

The benefits we get from the HEI system is simplicity, reliabilily, and plenty of spark! We particularily like the large cap, it keeps the spark from arcing to the wrong terminal inside the cap.

The only disadvantage of the HEI is the lack of a rev limiter. I guess you could deem point bounce a rev limiter.

Stock HEI is not intended for high RPM (5000+ RPM), but upgrade modules are available for such applications. Beware of coils that advertise more voltage (at the cost of less current), what is useful is more energy. The breakover and ionized voltage will be determined by the geometry of your combustion chamber; the ignition can only control the current. HEI are available with computer controlled advance; I would only use one if converting to electronic fuel injection

Factory Option:
HEI was offered as an option on 1974 (available in last half of 1973) Oldsmobiles, and became standard in 1975. Sales literature and parts catalogs all indicate this. For 1973 models a "unitized" ignition system was offered. From the illustrations it looks similar to HEI (coil in cap, etc.) but with some differences.

[ Thanks to Bruce Roe for this information. ]

Technical Overview

HEI Types:
This non-computer controlled version (used 1974 - 1979) is referred to as the 4-wire HEI, as there are four wires (or connectors) that attach to the module. It also uses a vacuum advance pot. In Canada, carbureted V-8 (haven't checked V-6's) models didn't receive CCC until 1986. Therefore, some Canadian '80-'85 models could serve as HEI donors.

A 5-wire HEI was also used for a few years. The fifth wire exits the dist. on the opposite side from the usual wires, and this one still has the vacuum advance. Indications are that the 5th wire goes to a special knock sensor. This sensor module instructs the HEI module to retard timing if knock is detected. This is a pre-computer attempt at timing control.

I think the system you are referring to is known as ESS (Electronic Spark Selection). Basically, the ESS decoder advances or retards the spark curve in response to the following inputs: engine vacuum, coolant temperature, crank signal. A delayed spark is desirable during cranking to reduce the load on the starting system, especially on a hot engine. The spark is advanced above the normal setting during cruise conditions, identified by a high manifold vacuum and greater than 1350 rpm (1200 for some) engine speed. The spark isn't modified during other conditions. The preceding is from a 1980 Cadillac service manual. Olds V8's didn't receive a knock sensor until '88.

There is also a 7 wire HEI distributor and module used on later computer controlled cars. This HEI has no vacuum advance pot as the computer controls that function. The 7 wire HEI was used in Olds models from 1980 to 1988 (Cutlass), and possibly 1990 (Custom Cruiser). Probably any carb equipped engine within these years is a donor for this 7 wire HEI. Modules don't interchange between 4 and 7 wire. The 7 wire are more expensive as well.

The HEI coil is different from 1974-75, 1976-79 and 1980-onward. Basically in the resistance of the secondarys.

The GM service part for the wire harness from the coil to the module was updated at some time. The newer harness (p/n 1892261) has a moulded plug for the module instead of seperate spade terminals and has the capacitor built in.

HEI to use:
When replacing a points distributor, you will want to use the 4-wire HEI found on 1974 to 1979 vehicles. The same Olds HEI or points distributor will drop into a 330, 425, 350, 455, 403, 260, or 307.

All 1964-1990 (except 394) Olds engine distributors interchange, including points distributors. Since, each GM division used a distributor with unique shaft dimensions, you will need to get one from an Olds engine to work in an Olds engine. Buick for Buick, etc. The aluminum shaft of the distributor is unique for Olds, having distinctive shapes to parts of the shaft. It usually has some blue overspray on the shaft as well.

In regards to which HEI is more performance oriented, well, you'll have to figure that out yourself, but in general, they are all about the same. For more performance, the distributor will have to be recurved. See the Tuning section.

There are lots of HEIs in the salvage yards for cheap. A 1979 Firebird 403 would be good; a 1979 Toronado 350 may have a better curve. Grab the wires too if converting (for 12V and tack). A lot of places have rebuilt ones; a few build them from scratch (translation: expensive). Get new plug wires and cap at least. Probably some work will be required to clean, lube, and recurve them.

Number of Wires Needed:
Since the points system uses a start circuit (full 12 V) and a run circuit (with resistance in line) there will actually be two wires. You must replace the resistance wire with a standard wire (or bypass the resistor wire) to ensure a full 12 volts to the coil at all times. You end up connecting the start and run wires to the single connection on the HEI. So there is only one connection but both ignition wires on that connection.

The coil sits in the top of the HEI distributor cap.

The body of the distributor still contacts the block, but the hold down clamp and bolt act as the primary ground. There's also the cam gear, oil pump shaft, etc. There are plenty of places to act as a ground.

Hooking up a Rally Pac:
This gets connected to the "TACH" terminal on the HEI coil where the rest of the wires connect on the HEI coil. You will find the words "BAT" and "TACH" topside of where to connect your tack wire. Use a spade terminal. Aftermarket tacks are plugged in here also.

Distributor Shaft Free Play:
There should be a little play, but rule of thumb, the less play the better. If you hold the body of the HEI in one hand and grab the drive shaft in the other I get about 0.05" - 0.1" of axial motion. Check the mechanical advance weights and make sure they are free. WD-40 to the rescue again! Although you do want to wipe up as much WD-40 as possible to keep from attracting dirt.

Testing the HEI Unit Before Cutting Wires:
Just to test the thing out before patching in wires and disconnecting others, you could just swap in the HEI and run a jumper wire straight to the (+) positive battery post. It shouldn't hurt to drive around the block a few times. You won't be able to shut off the engine unless you add a switch to your jumper wire. But you shouldn't be worrying about patching wires. This upgrade will benefit you tremendously. Just do it.

Maintenence and Replacement Parts:
I've heard alot of people say they don't trust the HEI modules since they can just go, but just keep one in the glovebox as a spare. And alot of people will also tell you that with points at least I can see what's wrong, etc. but with most electronics today, it's not a problem normally (you didn't buy cheap stuff, and save money, right?), and any problem with the units when they came out (heat, vibration, unreliable) has been worked out over the years. There are also millions of spare parts available for these units everywhere.

Distributors wear out like everything else; it takes a lot longer if they are properly lubricated. The oil rail (in an Olds) for the drivers side valve lifters ends just before the distributer. It should have a pipe plug with a .040" hole to spray oil on the distributor gear. If someone put in a plug with no hole, the gears and lower distributor bearing will have a short life. The lower bearing must take the strain of driving the oil pump, and it may be worn oval shaped. Fortunately it can be replaced, but a special size reamer is needed to finish it (yes, I have one). The upper bearing will have a long unstressed life, providing you repack the grease cup around it at reasonable intervals. Because of the pickup coil retainer groove and lube holes, the only satisfactory replacements I have found are used ones from a "donner" unit (like a Pontiac or Chevy). If the pickup coil is so old the insulation on the wires is cracking, a new assembly can be purchased. Napa has them, but Rasco is a lot cheaper. Weight pivots tend to wear; I put a tiny bit of brakelube on them frequently to slow this down. If its too late, there are pivot repair kits (an oversized plasic bearing over the pin). Last resort is a new shaft assembly. The cap and wires have a long life, esp if you use premium parts. However I would not try to run the same set over the life of my car (300,000+ mi). I run coils and modules until they fail, a rare event.

Clearing A Dual Snorkel Air Cleaner:
If you need a dual snorkle to clear the HEI, get a 74 dual snorkle. Designed to clear HEI. Hard to find but at least you don't have to ruin another.

The '76 Toro distributor is designed to have the cap mount 180° off. As long as it is set up as it should be in a '76 Toro, all will be well. My suspicions are more on the line that the module (you mentioned that a new one had been put in) is the generic "all except Toro" module instead of the correct one for the '76 Toro distributor.

Costs and Time Required:
This should take no more than 2 hours, unless you have that great combination of 455 and A/C, in which case you will have to add 4 hours to get to plug #8. Just kidding, it is quite easy to get to from underneath.

~$50-$100 and one hour, to install a junkyard HEI.
~$80 and one hour, to install a Pertronix Ignitor.
~$150 and one hour, to install a Mallory electronic conversion.
~$250 and one hour, to install an aftermarket electronic distributor.

Add another hour or two (or three or four or...) if this is your first time replacing a distributor and working with automotive electronics.

I spent about $220 in total. Time was about 4 hours total. Would have been about two hours less if I hadn't spent so much time trying to make it work with only a "run" position 12V source.

Distributor $150
Coil, cap and rotor $25
R46SX plugs (AC) $16
HEI wires $25
Cap and plug from junk yard $5 (took the cap just to get the ground strap under the coil).

If you want to chance a junk yard distributor you can probably get it (complete), for less than $40.

Oh, and if you don't already have an internally regulated alternator, you'll need to buy one of those. I think they're about $35 to $40 rebuilt (usually with $15 core charge rebate).

Even with all new parts it was worth it to me.

[ Thanks to Bob Valentine, Ken Snyder, Fred Nissen, Bruce Roe, Mick Gillespie for this information. ]
Early Olds Rocket Engines:
No HEI unit will fit because the 1949 - 1964 303, 324, 371 and 394 engines are physically different than the 1964+ Olds V-8's.
[ Thanks to Bruce Roe for this information. ]

Sourcing Parts

Salvage Yard:
I'm in the middle of gradually accumulating HEI components now for my own swap (although I may still end up not doing it). Here's what I have discovered. I don't think newer ones are a better quality, per se, just more likely to have fewer miles, which is important. Get the distributor that has the least number of miles on it. All the internal electronic parts are replaceable and are available from SuperCars Unlimited and Year One. The main worry about the distributor itself is wear of the bushings and shaft, which can be expensive to replace. As for comparing '75 and '76, I ~believe~ the internals are the same on those two. The FAQ lists differences in ignition coils for different years. I know, for example that there are coils that have red, black, and yellow wires and others that have red, black, and white. I think the main difference among those is in the resistance of the primary circuit. If anyone can comment on the better of the two, I'd be interested.

After taking my distributor to the shop to have the lower bushing made, I want to pass a word of warning along. Maybe some of you know this, but I just learned it. That lower bushing is the first thing to physically go in these distributors. And it ruins the shaft. Cost me $35 to get the bushing made and pressed in, but I still have to come up with a new shaft (computer ones, unfortunately, have a slightly different set up on the top) that I didn't know about until I pulled it apart completely. What a disappointment. I will now be careful to check that on every distributor that I pull.

If you go with a junkyard, GM HEI, make sure everything is working. The best bet is to get a new (rebuilt) one and also buy a new cap, coil and rotor. Oh yeah, get the connector for the 12v source and the tach to plug into, and also the ground strap that fits under the coil (this doesn't come with a rebuilt unit). So you'll have to go to the bone yard. If you grab the whole cap, it's easy to see how the new one should hook up and they probably won't charge more than $5. Mick Gillespie

[ Thanks to Mike Bloomer, Thomas Smith, Dorian Yeager for this information. ]

Conversion Procedure

I'm convinced, give me the steps to convert!

Installation procedure is as follows (details follow this list):

  1. Remove the old distributor.
  2. Install the HEI unit.
  3. Change plugs to HEI resistor plugs.
  4. Change plug wires to HEI wires and install them.
  5. Sort out the wiring, and Perform the electrical hookup.
  6. Start the car and set the timing.
  7. Perform some might-as-wells..

Remove the Old Distributor:
The installation of the HEI unit will be easier if you turn the crankshaft so that cylinder #1 is at TDC and index the outside of the HEI housing.

You will also remove the coil, plug wires and wire from the starter solenoid stud labeled 'R'. This wire is specific to points ignition. It feeds 12 volts to the points when the starter is turning, and the 'S' solenoid stud feeds 9.6 volts while the engine is running. HEI runs on 12 volts whether in run or start.

Always remove the low voltage wiring from ANY distributor before pulling it. Otherwise a spark could occur when the shaft separates from the block at that location, possibly causing crankcase fumes to explode.

Bring the engine to TDC BEFORE taking out the old distributor. Do it by taking off the dist. cap and jogging it over until your rotor is pointing at #1 spark plug wire position. Confirm that your timing mark on the balancer is also close to the 0 deg position on the timing plate. If you can't see the saw cut, it might mean that the balancer has to be replaced, or a repair sleeve installed. It might also mean that your timing was out a mile to begin with. When you install the new distributor, all you have to do is line up the rotor at #1 position and drop it in. Try to keep the vacuum advance cannistor in roughly the same position as the old one. This is a whole lot better than trying to find TDC with your thumb over the #1 spark plug hole.

The majority of the problems are due to a hardened O ring on the dist shaft combined with a build up of "gunk". On ones that are particularly stubborn, try working in some kind of solvent like carb cleaner. By working it back and forth it will give the solvent a chance to loosen things up. Also make sure that the dist shaft isn't binding against the cam gear as it comes out. It will have to rotate backwards about 1/4 of a turn before it disengages from the cam.

The problem will be that the oil pump drive rod, which is held in place in the block by a washer, is also stuck in the bottom of the distributor. It's a hex-shaped drive rod, and the bottom of the distributor has a 5/16" hex-shaped hole (yeah, I guess you could use an Olds distributor as a socket wrench...), and the points of the drive rod eventually get worn into the flats of the hole.

Try grabbing the distributor shaft and pushing back and forth. Then yank the distributor up and down. Now try pulling the distributor up and out of the block. This should get most distributors out.

If not, try a lot of yanking and tapping. Try tapping on the top of distributor drive shaft (remove all parts above the shaft itself) with a drift punch, yank up on the distributor a couple times (it should move up about a ¼"-½" or so, doesn't it?), tap some more, yank some more, tap, yank, tap, yank, and so on, until it comes free.

One of two things will happen: either the oil pump drive rod will loosen up, and you'll be able to pull out the distributor alone, or (more likely), the washer retaining the oil pump drive rod will come loose or break, and settle in the bottom of your oil pan. If the second happens, don't worry, the washer will just sit there, perhaps adding to the stuff already clogging your oil pump screen, but not enough to hurt anything, and you can just drop the driveshaft back into the block (the rod will stay in place fine without the washer).

Install the HEI Unit:
Hopefully you turned the engine over so the #1 cylinder is at TDC, and marked on the firewall where the old points rotor was pointing. If not and the points distributor is still in the block, do that now.

Put the HEI distributor in the hole, and line up the rotor with the firewall mark. Wiggle the distributor a bit to get it to seat in the hole. Now check cleanences with the firewall. The advance unit should not be right up against the firewall. Try about 1" or so in order to initially fire the engine. You will set the timing more accurately later.

Change Plugs:
When I converted my 1970 Cutlass to HEI, it ran badly until I regapped the plugs from 0.030 to 0.065. I had newish platinum plugs and figured I'd give the old ones a try.

If you have converted to HEI, you might notice a shortage, or absense of spark plugs for your Olds engine. An appropriate substitute is AC-Delco R46SX. When using R46SX plugs, the book says to gap them at .080" but try .060". It make a difference in power with no harmful effects.

I found out today that the SX series of AC plugs has been superceded by the SZ series and a local NAPA store was able to order them for me.

With the MSD you might try getting something a bit heavier duty, perhaps platinum or if they make the "truck plug" version of the R46SX.

If you are using the MSD 6AL box, I would recommend NGK 5670-6 spark plugs. They are like the NGK X45 but a little better. These plugs are set at .040" gap. Make sure your timing is set at 36° total. The inital advance should be around 18° if you installed a recurve kit. If not, buy the kit, and put on one light spring and one medium spring, and that will get the timing close.

Basically you run the largest gap possible. The larger the gap, the greater the voltage required to jump the gap. The greater the voltage - the sooner the leakage - the sooner the cross-fire etc.

Bottom line, with a stock rotor, your pretty much stuck with the stock gap. HEI systems can take up to a .060" or even larger gap. Most engines are good for about .035". Higher cylinder pressures will require higher voltages to jump the gap - you might need to upgrade wires to accomplish this without cross-fire.

I have experiemented with gaps - going from .025" to .060" on a stock system. The car basically ran the same. With the .060" gap it sometimes misfired at idle and high rpm. The factory manual calls for .035" and .045" works fine. Without dyno testing I couldn't tell what was optimal.

I guess the standard ignition system rules apply - if it fires all cylinders under all conditions than don't mess with it (save your time and money).

Don't reduce the resistor spark plug gap to that of the non-resistor plug gap (from .060" to .030"). This prevents the HEI from providing its best advantage, a hotter spark. Electricity will jump to ground as soon as it can. The smaller gap reduces the voltage in the spark to no better than the points setup.

[ Thanks to Mark Prince, Tom Lentz, Scott Parker, Bruce Roe, Dirk for this information. ]

Change Plug Wires:
The wires from your points ignition are for non-resistor spark plugs, while HEI uses resistor spark plugs and wires. For a bit more than generic HEI replacement wires, you can buy a set of performance resistor HEI compatible wires.

Sort out the Wiring and Perform the Electrical Hookup:
The HEI cap has 4 connectors. 2 are taken up by a connector from the distributor. One is for the TACH, and is so marked. The last one is marked BAT, and that's where you feed it 12v. Mine is wired straight from the fusebox to the HEI, but you can use any 12v source which is activated by the ignition key. I am sure there are "prettier solutions than going through the fusebox, but I was in a hurry and that was the easiest way to do it. You could also use this as an excuse to install a hidden kill switch.

The only wiring involved is finding the switched 12v source (hot with ignition key in "START" and "RUN" positions) and running a wire to the HEI BAT terminal.

The existing points distributor wire contains a resistor wire, which knocks the voltage down to 9.6 volts. Follow that wire back to find out either 1) where to eliminate the resistor, or 2) which wire not to use. If you eliminate the resister, you can use that wire to supply 12 volts to the coil. If you decide to leave the wire alone and patch in a new wire, just disconnect and safely secure the bare ends of this points distributor wire. Maybe put some shrink wrap tubing on the ends.

Just don't splice into the points supply wire and use it for the coil. HEI needs a full 12V. You need to get rid of the resistance wire completely. You also need this HEI supply wire to be hot, both for cranking and in "run" mode. You can't use an alternator wire for this. The easiest way is to follow the "resistance" wire into your fuse block. It plugs in to the position marked "IGN" with a spade connector. Just plug the HEI supply wire in that position, removing the points supply wire. This gives you all the connections you need except the tach.

Plug your tach into the HEI in the position marked "Tach". You also need to disconnect or remove the Hot wire from your starter that connects to the old coil.

Finally, clean all of your electrical connections thoroughly and apply some dielectric grease. Even if they look clean, don't assume they are. I even had to replace my negative ground connector on the battery cable. It looked perfect from the outside but was dirty and out of round enough that it wasn't getting a consistantly good connection. My cranking power doubled when I replaced it.

Resistor Wire
The resistor mentioned above is actually a nichrome (sp?) resistance wire; Mopar uses a conventional sand resistor, and I don't remember what dorF uses. I've also fixed a few which would start only when the key was *released* from the start position.

You either have a porcelin ballast resistor or a resistor wire: a ballast resistor is hard to miss. It looks like a small rectangular box and is porcelin; a resistor wire is almost always covered with a woven material and is usually silver.

In a point system you can tell if you have a resistor or not by connecting a volt meter to the plus side of the coil and to the negative battery post, make sure the points are closed, iginition key should be turned to run position, if you have 6 volts there is a resistor present.

HEI Feed
The best way to find power for your HEI (at least it's how I've done it on 20 or so conversions) is to take it from the fuse panel. Get out your test light and find one of the spare terminals which lights the test light in both run (ignition key in "run" position) *AND* start (key in start position). Hook a wire from here to the HEI's "BAT" terminal and you're set to go.

There was an empty receptor in the fuse panel marked "IGN" on my 69. By plugging into this, I was able to eliminate the wire from the starter. Just a guess, but I would assume the resistor wire gets (+) voltage only in the run position. If it got both, there probably wouldn't be a need for the "S" wire on the starter.

The 12 volt source has to be hot when the ignition is on, but it must also be 12v at the start position (while cranking). I finally ended up finding the IGN. position on my fuse panel and using that. If your lettering is worn off the panel, try tracing back the old resistance wire that want to the positive coil terminal on your old setup. You can check the fuse panel with a test light if you don't have a spot clearly marked. If that doesn't work, there is a diagram in the chassis manual, that shows the fuse panel and all the connection locations. You could also run a second wire from the "R" terminal on the starter and you will be sure you have 12V for cranking. You would just splice the two together.

I ran a #14 wire from the fuse box on the ign terminal through the hole on the firewall where the A/C wiring harness goes through. Nice and clean because the hole is right behind the distributor.

There is a power window terminal on the fuse block. This supplied power to a relay, through the ignition switch. The main feed for the window motors came from the horn relay/junction block, through a 30 amp circuit breaker, and then to one side of the relay. When the key was turned to the "on" position, the relay was pulled in, completing the circuit.

One wire from the ignition switch to the BAT connection on the HEI unit.

Keep in mind, if you are replacing an original points unit, the wire, purple I think, from the fire wall to coil, is a resistor wire. This is to lower the voltage to the coil. You need to replace this wire with a regular non resistor wire.

I went to the junk yard and pulled the entire wiring harness from the fire wall from a donor 71. I then pressed the spade connector out of the molding then did the same with my molding and pushed in the non resistor wire.

I know I'm not being clear but just make sure the wire connected to your distributor is not a resistor wire or you will not get as strong a spark.

You can run your twelve volt wire right off the iginition switch or splice on to a wire going into the fuse panel, but not directly to a fuse; because this wire will get hot.

Start the Car and Set the Timing:
Check cleanences with the firewall. The advance unit should not be right up against the firewall. Try about 1" or so in order to initially fire the engine. You will set the timing more accurately once the engine is running.

Start the engine. You may have to retard (move distributor counter-clockwise) or advance (move distributor clockwise) to get the engine to start. Once running, make sure you disconnect and plug any vacuum advance on the distributor, to set you initial timing. Of course you want to reconnect the vacuum advance later.

See the Tuning section for timing details.

Recommended Might-as-wells:
See the Conversion Recommendations section.

[ Thanks to Bob Valentine, Mick Gillespie, Bruce Roe, Thomas Smith Mike Schlottman for this information. ]

Conversion Testing

The first thing to check on your HEI conversion is the 12V source. The point distributor had a series ballast resistor somewhere, which is shorted out when starting. Sometimes its just a special high resistance wire between the ignition switch and the coil. This resistor must be shorted out for an HEI distributor. A test for this is connecting a wire directly between the HEI input and the battery (alternator stud is good); if the problem stops you need to fix your IGN wiring. Of course you will need to pull the wire to stop the engine.

If you are not sure you have voltage while cranking you can run a wire from the starter solenoid (R terminal) into the wire you are using for your twelve volt source.

Any ballast resistor circuits will have to be eliminated. The HEI needs pure 12V.

I've done two conversions to HEI for my 66 big cars. Once you get 'em running they're truly better than points. I'd go get a known good module (i.e. new) and known good coil (i.e. new) and substitute them for your boneyard parts.

These have been critical to the functionality of my HEI's. In one case my coil went bad and the car stopped dead. Dead. With the module there's really no alternative to replacing it since it is electronic.

Be sure that once the car is running that you've got a full 12 volts to the BAT terminal on the HEI. I think you're right that you need to remove the ballast resistor, not put one on.

If you pull the HEI back out of the car, you might check for distributor sloppiness. Like lots of up/down travel of the shaft, or the ability to move the shaft around inside it's housing.

Be aware that I rewired the switched BAT lead with thick (~10gauge) red wire in place of the original distributor lead. This neatly removed the ballast resistor and insured minimal resistance between the ignition switch and the HEI unit.

The only dumb (or supposedly so) thing I did was to also run the electric choke wire off that big 10 guage lead as well. I've not had problems but some listers feel very strongly about not doing this.

[ Thanks to Chris Fair for this information. ]

HEI Trouble Shooting

Clean it up and look at the clear epoxy for signs of arcing to ground.
   |         |   (View of an upside down HEI coil)
   |    _    |
   |   /A\   |      A - coil secondary output terminal (where the
   |   \_/   |          carbon brush spring makes contact)
   |         |      B - RED wire (BATT terminal connects here)
   |_________|      C - BLACK ground (held down by a coil mounting screw)
      | | |         D - YELLOW (or WHITE) wire (TACH terminal)
      | | |
      B C D
Using this chart, make the following Ohm Meter tests. Any failing test means replacing the coil.
Probe Points Expected Results
B-D about 1.6 ohms
A-C 8.1-8.2 kiloohms
B-C & C-D > 1.2 megaohms, but not infinite
A-B & A-D infinite

Check if the ground strap is in the coil. A broken or loose strap will arc, making a sound like the advance weights clicking against the side of the cap. Some new kits don't come with this strap and many forget to put it on.

GM HEI (internal coil) 1974-1975 6k-30k ohms secondary GM HEI (internal coil) 1976-1979 Infinity GM HEI (internal coil) 1980- (see text)

The resistance between the primary terminals of the coil should be no more than 1.0 ohms. The resistance between the secondary output terminal and the primary should be between 6k and 30k ohms. Integral coils on applications later than 1975 should have infinte ohms between the secondary and the primary. However, 1980 and later applications should be replaced if there is infinte ohms between both the primary and tach lead. This is also true of applications later than 1980 with an externally mounted coil.

Q: My question is why measure for DC resistance between one lead of the secondary and a lead of the primary anyway? Shouldn't this always be infinte?

It would for what you might think of as a regular transformer but the coil is an "autotransformer" -- no pun intended. It's like a transformer with a centertap and no secondary. The "primary" would be from the centertap to one side. The "secondary" across both sides like so:

Secondary -> ----)
|                )
|                )
|    Primary ----)
|       |        )
|       |        )
|-->    |--> ----)

So the primary and the seconday windings aren't electrically isolated from each other.

    C    B                 G    W
    __   __               __   __
    \_\_ \_\             /_/__/_/
     \      \___________/      /
      \                       /
       \   (G)        (  )   /
Modules I've seen have the terminals labeled. This may help if yours isn't. The (G) is the ground terminal, and it is one of the holes that the screw runs through to attach the module to the distributor.

  1. Remove the module from the distributor. (watch out for that nasty dielectric grease on the underside, It's relatively hamless, but goopy) Connect a test lamp between the B and C module terminals and jumper +12 volts to the B terminal and then ground the module at the (G) terminal. If the lamp lights then the module is bad.
  2. If the module passes step one, then jumper between the B and G terminals. The lamp will light if the module is ok.

If you suspect the module at this point, you might as well take it with you to the parts store if they'll test it for you, and confirm your diagnosis before you buy a new one.

Pickup Coil:

  1. Remove the pickup coil leads (carefully) from the module. Connect the ohmmeter to the base of the distributor and the pickup coil lead. The book doesn't specify which one, so I assume either one will do. Personally, I checked both. Operate the vacuum advance through it's full range. (I didn't have my vacuum pump with me so I sucked on the vacuum line going to the advance. If you use that method you're likely to spend the rest of the day spitting. I don't reccomend it, but it'll do in a pinch.) The meter should read infinite in all positions.
  2. Connect the ohmmeter between the leads coming from the pickup coil and operate the vacuum advance through it's full range with a vacuum pump. The meter should read 650 to 850 ohms in all advance positions.

Conversion Results

Took about 2 hours (took a half hour just to get the old one out!) to replace it, make the plug wires and set the timing.

Went done the road to do a burnout, what a difference! Before I could lay rubber until about 30mph and get a good 1-2 second chirp when I shifted into 2nd. Now it layed rubber to 60mph! The car runs smoother, takes off better and really runs like a bat out of hell when I punch at 80mph. Take my advice, get an HEI.

I did NOT have to dent my aircleaner. The Accel super coil has a lip that extends over the plug wire on the distributor that was in the way. I simply pulled out the Dremel, cut it off and the OAI airclener base just fits.

The conversion to HEI is complete and the car has never run better. It feels like I have 455 in there ;-). I highly recommend this conversion to anyone who is still running points.

Starting, hot, or cold is instantaneous and it runs through the gears (took it up to 5000 rpm max.) like a true muscle car ;-). I foresee better gas mileage too, as a lot less throttle seems to be needed to get up to cruising speed.

[ Thanks to Mick Gillespie for this information. ]

Post Conversion Recommendations

Air Cleaner:
Get the air cleaner assembly from an HEI engine as well, as the original air cleaner will hit the HEI distributor cap. There may be some air cleaner clearance problems; the HEI engines tended to use an air cleaner shifted forward instead of centered around the carb.

You might want to massage the original cleaner housing, but there is a sort of more elegant solution. A trimmed tomato juice can is used to space the air cleaner up about a 1". Spacers and adapters are frequently included in aftermarket one-fits-all chrome aircleaner. But a Rochester 4V has a smaller ring diameter. This solution is pretty clever, and the basic approach applies to all carbs/air cleaner housings.

Coil and Module:
The HEI should work fine for street motors, and if you're concerned about getting a hotter spark, you can replace the stock coil w/an aftermarket one for reasonable money. Of course, if you like the RPM limiter (don't need for an auto trans unless you manual shift, of course), then spring for the aftermarket types. Be careful of the type of rev limiter used with an HEI and other electronic ignitions since some styles can damage them. If I want that capability, I'd probably get an MSD 6A-L or equivalent.

Electronically Regulated Alternator:
You must convert to a electronically regulated (non-vibrating regulator) alternator. Converting externally regulated GM alternators (pre 1971) to internally regulated post-71 alternators is a relativly easy affair. You will be burning out HEI modules at record pace if this is not done!

I took a look at the mechanical regulator and I could see how it would give my HEI a hard time, causing it to fail shorty after installation. One set of points in the regulator is eaten up pretty bad, and it turns out the regulator was causing some problems with dim lights, and what appeared to be generally low battery voltage. When I started the car after installing the new regulator the ammeter indicated about a 25 amp charge. The mechanical regulator was not correctly sensing the battery's charge.

My '71 had the mechanical regulator stock from the factory. However, my Olds Service Manual indicates some cars of that year had the solid-state regulators in the alternator. To check, if you see a black box above the distributor about 3" square on the firewall you likely have a mechanical regulator. I say, "likely," because some replacement, aftermarket regulators are made now that install in the same location and look the similar but have solid-state, electronic guts.

To confirm whether or not you have a mechanical regulator or an electronic replacement, disconnect the battery negative cable (this will ensure you don't short out and destroy the regulator in the event it is electronic). Take off the regulator cover. If you see what looks like thin metal blades with contact points on them, you have a mechanical regulator. You may also see a little plastic adjustment knob.

Now, to eliminate any question, look at the plug going into the alternator. If it is about 1/2 inch square, you have an externally regulated alternator. If the connector is flat, about 1/4 inch wide by 1 inch long, you have a solid-state alternator EVEN IF you appear to have an external regulator on the firewall. The reason I say this is that there is this nifty procedure in the FAQ that tells how to convert to an internally-regulated, solid state alternator and disable and jumper the original regulator. This allows you to keep the regulator on the firewall for a nearly stock look.

My point is, if the alternator has the externally-regulated style plug (the square one) it may still have electronic regulation if the regulator has been replaced. BUT, if you have what looks like the internally-regulated style plug (the flat one) you definitely have an internal, electronically regulated alternator, even if you have a regulator box on the firewall.

You'll have to check and see what you've got. BTW, if you have the older, externally regulated alternator, BUT have an electronic replacement regulator, the FAQ indicates you don't need to change alternators to go to HEI.

Setting Initial and Vacuum Advance:
Please note that HEI's are curved way different than the pre-emissions points distributors. There are kits to handle the weights/springs for the mechanical advance available at most stores. For an auto tranny you would like to have total mechanical advance in by about 2500 rpm. You check this with a timing light and tach. See the Tuning section.

Getting your HEI checked out and recurved against the old unit will work; doing it yourself is cheaper. For vacuum I use a hand vac pump gauge. With the vac canister out observe how much vacuum is needed to start it moving, and how much vacuum at maximum advance. And with a 6" dial caliper, how many thousands total movement?. Mine show about .300" movement, which translates to 24° on the engine. If your HEI vac unit is a bad match, get an adjustable one. This can be set for total travel, and advance starting point. If these match on the bench, they should match on the engine

I set mechanical advance on the engine. First make sure your timing chain is reasonably tight (you DID replace it, didn't you?). See how many degrees you can rock the crank back and forth before the rotor moves. More than a couple degrees is bad. Put a tachometer on to see RPM. Disconnect vacuum advance to avoid confusion, and temporarily move up timing so engine runs OK. While slowly speeding up engine, observe RPM where first starts (use a timing light, we are just looking for change, not absolute timing). Observe RPM and amount of advance at several points up to maximum advance. With these measurements on the original distributor, do the same on the HEI. Change springs or weights as Fred said till the HEI is close to the original. You can use the same method to check the vacuum advance by keeping engine speed below where mechanical advance starts, and use the hand vacuum pump while obseving advance

Once the two units match, connect vacuum and set timing to spec. Trying it also a couple degrees either way is probably worth the test.

Then it comes down to getting the right mechanical and vacuum advance curves. Weight kits and adjustable vacuum canisters are available for the HEI. You can curve out your old and new units on your engine if a distributor machine is not available. With vacuum disconnected, note initial timing mark reading at idle, and change as RPM is increased to max. Possibly you will need to temporarily advance the distributor position (rotation) while testing to get the engine to run over the range without vacuum. Next measure vacuum advance using a vacuum hand pump. This must be done over a low RPM range where mechanical advance has not cut in, or bind the weights. This can also be done on the bench using a micrometer directly on the vacuum canister. If the advance arm is the same length, the movement of the vacuum activator should be the same. Set the screw to the point where advance just begins, and a cam is set to limit maximum advance

See the Tuning section for more details.

[ Notice: ]Please refer to the Tuning to optimally setup (timing, advance, etc) your HEI converted ignition.

[ Notice: ]Please refer to the Ext. Regulated to Int. Regulated Alternator Conversion section as well!

HEI Conversion Experiences

The major benefits I have seen are in easier starting and smoother performance. I don't think my gas mileage improved though, since I switched to a 4 barrel carb and a bigger cam at the same time; not to mention the big valves :-). I have revved it out to 6000 RPM once and it was still pulling strong.

The recurve kit did help performance noticeably, but after a lot of trial and error, I ended up using only one "medium" spring from the kit. Seriously, I like the HEI and electronicly regulated alternator much better. The reliability factor is a whole lot better in my opinion too. It's still an expensive proposition though, to switch out parts in perfectly good working condition and replace them with new ones. The only difficulty I remember, is forgetting that I needed my 12v source to be available in both the ignition "on" and "run" positions. The distributor fought back a bit getting it out, but a bit of wiggling and banging, and out it came.

I also added a spacer under my stock air cleaner for better clearance.

I've done the HEI swap, about a year ago. Any fuel economy benefits are negligible, compared to a well tuned points system. However, the improvement in smoothness is stunning, starting is easier, quicker, low end pull seems to be stronger. Easy swap to do, well worth it.

If the points don't really bother you then you it may not really be worth your while to do the swap. You ~may~ pick up a few mpg since you can run a larger gap on your plugs. I say may because it all depends on what your exact combination is and what other mods you make to take advantage of the HEI. You can usually richen up the carb some so that any given rpm you have to depress the throttle less to get the same amount of power, but as I said, it all depends on the whole combo. Rock solid reliability is the main cause of many making the switch since with an old car anything that gives you one less thing to worry about is usually worth it. If you think about the fact that the performance of points (effieciency) constantly degrades from the time you put them in and the HEI stays constant then that's something you have to consider.

[ Thanks to Mick Gillespie, Todd Morris, Mike Bloomer for this information. ]
[ Thanks to Chris Witt, Fernando Proietto, Pat Clark, Andrew Green, Bob Handren, Tom Lentz, Greg Pruett, Bob Barry, Joe Padavano, Graham Stewart, Scott Kozhill, Scott Mullen, Kevin Wong, Chris Fair, Erik Nowacki, Chris Ruper, Mark Prince, Rich Inacker, Todd Morris, Kurt Heinrich, Jeff Easton, Mike Frederick, Dorian Yeager for this information ]


Advance Curve / Recurving

You have an "initial" timing setting for idle and as the RPM's go up, the weights inside the distributor overcome the force of the springs preventing the weights from moving, due to centrifugal force. As these weights extent outward the timing advances, until they hit their stops. This is called mechanical advance. Between your initial and total mechanical settings, you have the advance curve or specific amount of timing at a certain RPM. If you plotted this on a graph it would look like a curve that starts adding just a little advance at first and more towards the total end. Vacuum advance can add a bit more timing advance over this curve. You need an adjustable timing light to really play with it, or a degreed balancer so you can watch the curve happen as you raise the rpm. By swapping in lighter or heavier wieghts and stronger and weaker springs, you can manipulate this curve in several different ways, but it is sort of a black art, and takes a bit of talent to get the most out of it.

The recurve is easy enough to do yourself, but a lot of trial and error is involved. You need a graduated timing light as mentioned (or timing Tape). I used the Moroso kit which is cheap and has lighter weights and two weights of spring. With your stock springs that makes three different weights of spring. You can calculate all the combinations and permatations. After a lot of messing around with varying combos, I ended up using both stock weights and a light spring on one side and the stock one on the other side. I also used a bushing that came with the kit to limit the amount of vacuum advance. Ended up with 34° total timing, all in by 2500 RPM. this is on a 69 350/350 with Edelbrock Total Power pkg. (heads excepted). I was originally after 36 deg at 2500 RPM and the car ran like a raped ape at mid to high RPM, but I couldn't get rid of a real rough idle and it would baff out starting off at light throttle. set it back to 34 deg. and it runs a lot smoother but I think I lost some performance. It takes a lot of patience (or luck), to get the curve where your car wants it.

If you plot the amount of centrifugal advance vs. rpm, you get a "curve" that is usually linear up to a maximum amount of advance. Different springs will adjust how soon that curve begins from the initial advance, as well as how long it takes to get to maximum advance. You can also include the vacuum advance in that curve, but because that advance is proportionate to engine vacuum, it's extremely variable, and usually not counted in what's referred to as the distributor "curve".

Recurving or setting the advance curve involves springs, and in extreme situations, new weights (either heavier or lighter) and limits or extensions to the slots or pins that regulate maximum advance. Springs and weights are included in a recurve kit.

You can do it by machine, where you match the amount of advance at certain rpms to some ideal curve. Or, you can do it yourself in about an hour's worth of testing, and create a custom curve that's ideal for your particular engine. There are many advance kits out there; I was happy with the Crane adjustable vacuum advance kit, which cost me $22.

The existing distributor curve may be ideal for your engine, or it may not. Usually, you want to have as much advance as you can, before detonation (spark knock) sets in. You want to find out how much total advance you can run, and try to get that much advance in there as soon as possible. The exact numbers are not all that important, which is why curving a distributor on a machine may or may not improve your car's performance, since the ideal curve that the distributor is set to on that may not be the ideal curve for your car. It's not just the cam that affects the ideal curve, but also gearing, transmission, engine condition and other modifications, jetting, fuel quality, driving style, atmospheric conditions, etc.

I'd recommend something like the Crane kit; follow its instructions, and you'll likely be happier with how the engine runs afterwards.

The various combinations of springs and wieghts available will determine the speed and rate of change of the mechanical advance. This is not a linear change (ie, a straight line if you graph it rpm by advance) but has a more rapid rate of change at either the lower or upper part of the RPM band. This is your curve. What is important is not to set the curve to exact specs but to what the engine wants. Because of this, you will eventually have to play with it on the car to get it exact. Variations in your combination (carb, cam, CR, ignition, etc) will make the optimal curve different for just about every engine. One curve may work from one engine to the next but still not be optimal. The adjustable vacuum advance comes after the distributor curve for fuel economy and drivability reasons. All you really need to curve a distributor is a fundamental understanding of how the advance operates, an adjustible timing light, an accurate tach, a curve kit with various springs and wieghts, and lots of patience. Most of the good curve kits come with instructions which will set you in the right direction. As long as you don't enter the detonation range just getting the curve close should be enough, since driving around town you really won't notice a difference of a few degrees here or there. If you were seriously drag racing however, you might find a few tenths. Hope this helps and wasn't too confusing.

A friend has a Sun distributor machine he picked up at an auction. Dates from the 1950s but everything works and it has all the documentation. It is quite a thing to see. It has a vacuum pump for the vac advance it drives the distributor with an electric motor. It has all sorts of dials to measure different parameters as it spins the distributor. I can tell you from watching it that you wouldn't want one of those advance weights to ever come loose at speed... it would be quite a violent collision with whatever it hit. A distributor really spins a lot!

He did mine last year. With a service manual for the specs you want it actually is pretty straightforward to check. With the machine you can see how the different weights will affect how much advance kicks in at a given RPM. Similarly with the vac advance. Also you can see how any variance or wobble in the bushings affects advance or dwell. Neat. I wonder how many of these machines are still in shops?

Race engines don't need vacuum advance, because they're never at part-throttle anyway. Any street engine spends more time at part-throttle than WOT, and can always benefit from having vacuum advance. Magazines like Hot Rod test engines at WOT (Wide Open Throttle) on a dyno, where vacuum advance plays no role, so they leave it off the engines. Then they tell you that you need 36 deg, or 32 deg, or whatever, of mechanical advance. They totally fail to inform you that your engine will run better on the street with additional vacuum advance over and beyond that 36° or whatever.

[ Thanks to Mick Gillespie, Robert Barry, Mike Bloomer, Greg Beaulieu, others below for this information. ]

Factory Setup and Information:
Delco produces a specification book called the "1.2" manual. The good news is that all distributor advance curves are listed. The bad news is that they are listed by distributor part number. You cannot just look up the curve for a "70 Toro". Fortunately the number is stamped into the distributor housing.

The centrifugal mechanism is subject to wear, which alters the curve. This is common on all distributors. The weights will cut into the pivot pins, sometimes shearing them off! The proper fix is to buy a new distributor mainshaft from GM. The last one I got was $60, had a "performance" curve built in, and fit a Che*y. Incidentally, that mainshaft "fixed" a number of "carburation" problems! There are repair kits to salvage the worn pins in the original mainshaft, they are a pain in the tuckus if you don't have a torch to heat the weights cherry red before trying to drill the pivot holes oversize. HEI's are especially bad for having worn centrifugal mechanisms because there was no need to remove the cap and rotor to replace points. No mechanic on commission is going to rip off the cap and rotor to lube the advance mechanism out of the goodness of his heart. Point style distributors needed the cap pulled off to replace the ponts, and so sometimes the advance was lubed at the same time.

The distributor bushings especially on points style distributors also wear, altering the timing in erratic ways.

Virtually all distributors from GM have WAYYYYYY too much end play, and should be shimmed so that end play is around .008-.015. This prevents dynamic timing changes due to the distributor gear jumping up and down on the cam gear. Since they are helical gears, vertical movement of the distributor gear causes the shaft to rotate, changing the timing.

[ Thanks to Schurkey Swanke, others below for this information. ]

Overall Advance Curve Information:
This discussion applies to points ignition or any distributor type ignition system. In any case, take this discussion as a guide, not written in stone. Every ignition systen will take some trial and error for maxiumu performance.

So much depends upon the characteristics of the motor, vehicle weight, axle ratio, etc., that no one setup is exactly the same, but the more info on all that stuff, the better. If you're getting part throttle ping, but are otherwise happy with the timing curve, you can always go to an adjustable vacuum canister and fiddle with that until you dial it out.

Please note that HEI's are curved way different than the pre-emissions points distributors. There are kits to handle the weights/springs for the mechanical advance available at most stores. For an auto tranny you would like to have total mechanical advance in by about 2500 rpm. You check this with a timing light and tach.

I'd suggest buying an advance kit with new weights and various springs so you can recurve the distributor. The factory HEI mechanical advance is very s-l-o-w, and the vacuum advance is way too much. Adjustable vacuum advance pots are available, or braze the slot to limit advance to about 10.

What you want to do is have similar advance specs to that of the points distributor. Full mechanical advance at 2000-2500 is ok for an automatic transmission. A standard transmission requires quicker advance, so it's full about 1500. Again, vacuum should be limited to no more than 15°.

The total amount of advance or overall advance depends on many things (compression ratio, head design, rear-end ratio, weight of your car, etc) but I've been told numbers of around 10° to 15° advance at idle, around 36° full mechanical advance (with the vacuum advance disconnected). At part throttle, high rpm, with vacuum advance, the ignition timing should be somewhere in the range of 50°. That number surprises many, but that's what's needed for maximum fuel economy at part throttle (cruising).

Total/overall advance is calculated as:
[total @ RPM @ inHG] = [initial] + [centrifugal @ RPM] + [vacuum @ inHg]
Centrifigal and mechanical advance mean / are the same adjustment / measurement.

Total advance at high rpm and wide open throttle = initial timing + mechanical advance

Total advance at high rpm and part-throttle = initial timing + mechanical advance + vacuum advance

One rule supercedes everything else: if the engine detonates, reduce the timing immediately till all traces of detonation are gone. Detonation will kill your engine in a very short time (it breaks piston rings, crumbles pistons, etc.).

The best way to set ignition timing is to modify the initial advance and advance curve to get the best power at WOT at all rpms. Do this with the vacuum advance disconnected. Once the mechanical advance is dialed in, connect the vacuum advance, and dial it in for best *part-throttle* power with no pinging or surging. This last step is universally omitted when the car magazines write about engine buildups.

There are two methods to setting and determining timing. One says be concerned about initial timing, the other says be concerned about overall timing. You should probably be concerned about both, letting neither negatively affect the other.

Try as I might, I cannot understand why an ignition kit would include "lighter springs and weights". The purpose of the the weights is to advance the timing as a result of the moment and rate they move due to centrifical force (the rotation of the distributor shaft). To change the point at which they begin to move and the rate of movement to their maximum swing is the function of the springs. The lighter the springs, the sooner and faster the weights swing to maximum (the earliest max advance)......the heavier the weights, the same result. To answer your question, to obtain the earliest movement and most rapid swing to maximum advance would entail either lighter springs or heavier weights; but not a combination of light/light or heavy/heavy.

I would say go with what Crane recommends. When curving the distributor the best way to go is to use the stock wieghts as a baseline. Go heavier on the springs to raise the rpm where you get total advance, lighter to lower it. A good curve kit will have an assortment of springs. For the wieghts, the opposite is true in that the heaver the weight the lower rpm for total and lighter to raise it. Keep in mind your initial and total timing points are only part of your curve. It's also how it gets there. Light springs will give a quicker jump off initial and level off near total. Heavy springs will give a more gradual advance off initial and be more rapid the closer it gets to total. That's why they call it a curve.

A good starting point is to use one light spring and one medium spring. You want total timing of 34-36° BTDC at 1500 to 1800 rpms. Initial timing will probably be at 14 to 18°. I use full mechanical advance and no vaccum advance. I also put a stopper in the distributor in order to not let the timing go beyond 36° total. A good rule of thumb for a street/strip combo is about 14-18° BTDC initial advance to approx. 35° at 3000 RPM maximum advance

The possible combinations of weights, springs, quantity and rate of advance do seem to make the task of determining timing to be fairly complex, very much like a trial and error operation. The ideal combination is quite dependant on compression, rear gear, intended use, cam, economy vs. performance priorities, etc. It is difficult to simply take a recommendation from a friend as to the correct settings, since that may not apply to your car.

While all this is true, it shouldn't be that hard. While a distributor machine makes it a piece of cake, one of the timing lights that give you timing advance values at each step works just as well. After all, your engine can do anything the distributor machine can.

What can also get confusing is that some of the advance curve kits recommend removing or replacing the sleeve over the pin in the mechanical advance mechanism. This makes using the original initial timing value a potential problem. A slightly different approach has worked for me.

You are correct that you should have full advance at 1500 dist. rpm which is 3000 engine rpm. Most of the 1966-72 Olds V-8 were factory set to have full advance in as soon as 3000 up to 4200 engine rpm.


Application Engine RPM Distributor
68 Toro/442 455 4 bbl 3000 #1111289/1111292
68 non-Toro 455 4 bbl 3600 #1111469
68 455 2 bbl (in what?) 4000 #1111288
all 66-67 425's 4000-4100

Plus other specs I have show other years are basically the same as these listings.

A 2.56:1 rear is a pretty darn stiff rear ratio, which means the engine sees a much bigger load (less torque multiplication through the rear gear). A bigger engine load means increased cylinder pressure and increased tendency to detonate. Translation: be cautious in going to lighter and lighter distributor springs, as your engine is working harder than most due to the very stiff rear end. Again what I've heard for Mopars is to use full advance by roughly 2500 - 3000 rpm.

If you can get away with full advance at lower rpm with no pinging, fine. Just be very careful not to run into even mild "silent detonation" which can still break piston rings and damage pistons without being loud enough for you to hear over the sound of the car. Once you find the point where the thing pings, back off a few degrees to give it a safety margin. Also a hotter day or a tank of bad gas might come your way and needs a safety cushion. Better an engine a few % down on torque than one that needs a rebuild due to detonation.

[ Thanks to Donny Arnold, others below for this information. ]

Initial Timing:
The general rule is to run as much intial advance as you can, (without making starting impossible), and make full throttle runs with various spring rates, (you can mix springs without hurting anything and actually advance the curve in steps). This should be done with no vacuum advance hooked up at all. Once your best performance is dialed in with no pinging, then go ahead and hook up your adjustable canister.

On the initial advance, assuming you still have decent compression, if the motor turns over after slight hesitation, (starter load), you're probably running at least 12° of initial advance. If not, it's probably something less.

[ Thanks to others below for this information. ]

Overall Timing:
For some reason a lot of people seem concerned about initial timing. It has virtually nothing to do with performance. The measurement you should focus on is total timing advance and the advance curve. You want as much advance as you can get, coming in at the lowest RPM possible without detonation. Put a timing tape on your harmonic balancer. Unplug the vacuum advance from the manifold vacuum and try various distributor springs to get your mechanical advance started around 1500 rpm and all in by 3000 rpm or so. One of those engine analyzers with a tach in it is crucial here to map out the amount of advance at a given RPM. Also, rev the motor right to 5500 rpm to check for timing scatter.

Don't set your timing with initial advance only. This tells you nothing about the total advance which is near or where the advance is while the engine is running at speed. This value only has meaning for a totally stock ignition system.

Disconnect the _vacuum_ advance and rev the engine up slowly while using a timing light. Measurer the total advance. This should usually not be more than 35-36°. Yes, your harmonic balancer isn't marked that high - so mark it. Measure the distance on the timing tab and add to the balancer marks already there. No, it won't be exact but is close enough for a start. Better way is to get a timing tape for the balancer from Mondello (expensive) or PAW (less expensive) or anywhere else that has one. They are made for Olds engines. The generic tape will be for a Chevy balancer.

Distributor curve with 12 deg initial advance
RPM Cent. Adv. Total Adv. (no vac)
1000 14°
1600 10° 22°
2300 15° 27°
2700 20° 32°
3000 24° 36°
Which looks like a pretty reasonable curve for premium gas and a CR around 9-9.5:1.

Total advance is the sum of

Total advance ought to be between 32° to 36° for most any non-emissions performance engine. As far as I know most stock HEI's produce over 40°. Get an adjustable vacuum advance from Crane (comes with an advance limiter). This kit also comes with springs to adjust the centrifugal advance. I have not found it necessary to change the stock weights to the aftermarket weights the Mr. Gasket, etc. kits come with although maybe you might want to try it to see if it helps your particular combo. It should work without problems with stock weights though.

It is important to check the top end (5000-6000 rpm) for timing fluctuations, as it is a good indicator of a worn/loose distributor. By using one of the timing lights with the adjustable dial on the back, you are only simulating the revs. Put a timing tape on the balancer ($10 from Summit) and rev the motor for real!

Make sure you are using the octane gas that you normally will run, and that you are testing on a day with average weather. Setting the timing on a 95° day will result in too mild of a curve, just as setting it on a 50° fall day will be too aggressive for summer driving. Intake air temperature and fuel octane have significant effects on detonation. Cooler air/higher octane fuel let you set a more agressive timing curve.

That's why the W-30 had OAI and a recurved distributor. You can then road test the car (with the vacuum advance disconnected) to find detonation at various rpms. Go back and try different spring/distributor cam/weight combinations to alter the curve to eliminate detonation spots. By drawing a curve on a graph (using the total advance measured at various rpms using your timing light and the timing tape) you can compare this curve with your observed detonation points and then reshape the curve with different springs/weights/ distributor cams to arrive at the desirable setting.

The first place I would suggest starting is with the specs Olds established for your engine in the first place. They can be found in a Motor manual covering the year of your car. Interestingly, my GM service manuals (for my cars anyway) don't give these values but Motor's does. Using a timing light you can set up the distrubutor advance characterisitics to match those of the original points distributor. But those values are the compromise settings given mass production tolerances, etc.

The other way is to match your distributor to your engines requirements. I usually don't pay much attention to initial advance at the beginning of this exercise because what you're looking for is actually the total advance, initial + mechanical + vacuum.

In-the-ballpark numbers are about 35 degress total initial and mechanical advance and limitation of vacuum advance to about 10-15°. Most of the HEI's I've played with have 20°+ of vacuum advance. Too much.

Disconnect the vacuum from the advance pot. Using a timing light with advance measurement capability, check and set the total initial + mechanical advance. You'd like the mechanical advance to be fully in by ~1500 to ~2500 rpm and be about ~35° total (without vacuum). Set the distributor at this total advance position. Depending on auto vs. manual, compression ratio, cam, etc. you may need a little less. I've found that an Olds engine usually doesn't like initial + mechanical (centrifugal) of more than 36°.

Since this early advance (compared to stock) usually means lighter springs than stock, the inital timing value is many times much different from published "tune-up" values and therefore pretty much irrelevent. My neighbor with a 66 GTO went bonkers trying to make the two agree (initial and mechanical) for a Mallory unit he was installing until I pointed this out. Took about 5 minutes after that.

When you have your mechanical advance curve set up, install a Crane adjustable vacuum advance and follow their instructions for setting it to eliminate part throttle opening detonation. I highly recommend this part. The next time someone asks you your initial timing setting, tell them you don't know/don't care, because you will have spent your effort where it counts, namely in setting the total advance and the advance curve. By using a stock GM HEI distributor, you are ensured a ready supply of cheap (usually free) parts and performance that is more than adequate for the serious street car. Have fun, wear safety glasses when revving the motor (in case of broken belts and the dirt flying around at 5500 rpm) and keep your fingers out of belts/fan blades.

[ Thanks to others below for this information. ]

Centrifugal (mechanical) Advance:
The centrifugal advance weights should be recurved to use with your older car that expects more timing. You can get a recurve kit at most speed shops for a few bucks that fits all HEI distributors. When installing it remember that Old's spin counterclockwise and it's a 99% sure thing that the instructions show a clockwise spinning Chevy, so reverse the weights. The kit consists of different weights along with a bushing to limit the total advance (if that's what you want), and a few different strengths of springs.

Remember that the advance weight set up is for a smog controlled car. Your car will work with the original setup, but it will feel a little sluggish. Buy the Accel re-curve kit. You will notice a big difference. When putting the re-curve you will need to re-set the initial timing as the lighter springs will cause the timing to become more advanced. You will hear pinging. So keep that in mind. When using the re-curve kits, use the lighter springs, not the weights. You only get one pair of weights and 3 pairs of springs in varying degrees of stiffness. If you use the lighter ones first (springs), re-adjust your timing.

I dug out my info on the factory HEI weights/cam set-ups that will give you more mechanical advance than normal. They are found in the following cars:

Engine Car Deg. Mech. Adv.
Olds 260 V-8 1975 Pontiac Ventura
1976 Pontiac Ventura
Olds 260 V-8 1975 Olds Cutlass, Buick Apollo/Skylark
1976 Olds Cutlass, Buick Apollo/Skylark
1977 Olds Cutlass, Buick Apollo/Skylark
26, 28°

Remember, you don't need the whole distributor, just the center cam and the advance weights. I'm using #139 weights and #410 (I think) distributor cam. This gives me around 29 deg of mechanical advance. I can thus set total advance (which is the sum of initial and mechanical) to 39-40 deg, and still have an initial of 10, which allows for easy starting. However, I don't care what the initial timing is, and I never check it (because it doesn't matter) other than when I've had the distributor out of the engine.

   \___ o|
    *  | |
    __/ /
   / 53/
Stock advance weights can be ground to allow for a greater amount of advance travel. I've found that if the area above the asterisk is ground down such that the ramp angle is changed on the left half of the 'active' area, the total range can be increased. The amount of clearance between the outer side of the weight and the inner walls of the rotor may be a limiting factor in extreme cases. BTW, what does the number on the weights refer to? Which weights are the heaviest? If I remember correctly, aren't #139 weights the ones with a thicker mid-section and narrow tip, versus the style I've depicted in ASCII, where the weight section is widest towards the tip? BTW, the lightest factory springs I've come across are from 1977 and 1978 425 Cadillacs.

[ Thanks to ,others below for this information. ]

Vacuum Advance:
Most of the adjustable advance canisters I've used do not advance at all when turned fully COUNTER clockwise. Keep making runs after two clockwise turns until you get pinging, then back off. As you have already found out, it is important to get the car up to operating temperature before you go through all of this or your perfect settings soon go bye-bye.

To check the vacuum advance, use a vacuum pump attached to the can and the same timing light. Adjust the vacuum max setting accordingly.

Remember this about vacuum advance. Under light loads/throttle, the intake charge velocity is lower and has less mass, therefore, it burns more slowly in the combustion chamber. For peak efficiency under these conditions, it is necessary to ignite the mixture earlier, so that peak cylinder pressures coincide with TDC. At heavier throttle, when the intake charge is greater and cylinder pressures are higher, less advance can be tolerated. In other words, vacuum advance units are used only for improved fuel economy, making better use of the air/fuel mixture under light load conditions.

Cars have over 60° advance with the vacuum included. Under part-throttle, low-load situations, the A/F mixture is spread all over the cylinders, so you have to start that stuff burning well in advance if you're to have it all burnt up by the time the piston reaches the top of the stroke, so you crank in lots of advance. Usually you run as much vacuum as you can before you start pinging; the exact number is irrelevant, since the pinging will depend upon the state of your engine, quality of fuel, driving habits and conditions, etc. Two identical engines in two different people's cars will require different amounts of vacuum advance, though the ideal distributor curve might be the same.

The idea behind vacuum advance is to add advance under low load, part throttle condtions (which 3000 RPM and 18 inHg would imply) where the engine can tolerate it. The additional advance tends to help fuel economy and (debatably) engine cooling. Really depends on how much vacuum your cam produces.

When your foot is to the floor (high load), vacuum approaches 0 inHg and the advance is out of the picture. My cam (JM 20/22) idles at about 15-16 inHg and I only see greater than 18 inHg at part throttle cruise so that would be about right. If your cam idles at 20 inHg, then that vacuum advance might result in detonation when you ease into the throttle if manifold vacuum doesn't drop below 18. You'd have about 22 (@ 1600, say) + 18 = 40 deg.

Most folks who drag race their cars disable the vacuum advance to allow more initial and centrifugal without having to worry about detonation when the vacuum starts to come up at the top of the last gear.

Even a minimal amount of vacuum advance seems to make a big difference on the low end - more torque. Although there is some pinging at highway speeds. A fix for this is to use a vacuum advance limiter plate. The Crane adjustable vacuum advance kit includes a plate that limits the amount of vacuum advance that the cannister can add. I found that I could reduce the rate or point at which the vacuum advance kicked in, but I was unable to eliminate the pinging at part throttle until I reduced the amount of vacuum advance, probably by about 10° or so from the maximum it would add.

On all but the earliest HEI's, the advance canisters provide way too much advance at way too little vacuum. Go to your local GM dealer parts department and get the HEI vacuum control P/N 1973511. This is the best available new. The so-called "adjustable" units. tend to die quickly, and only control total vacuum advance. They still come in too early.

If you want a limiter plate, and you don't want to spring the $22 for a whole Crane kit, you can probably make one from a small sheet of heavy-guage steel, or even a washer. Basically, it mounts under one of the screws holding down the vacuum advance unit, and forms a kind of "stop" to limit the travel of the rod that extends from the vacuum advance cannister. If you reduce the amount this rod can travel, you reduce the amount of vacuum advance that can be added; this limiter plate actually moves the starting point of the rod closer to the canniser itself (hence you have to adjust the initial timing with each adjustment), thereby reducing the rod's travel. The plate in the Crane kit has a kind of serrated edge, and you adjust the amount by loosening the screw, and turning the plate until the end of the rod rests on one of the serrations.

[ Thanks to others below for this information. ]

Vacuum Sources for Vacuum Advance:
Define a couple of needed terms:

Ported means that the vacuum signal varies with throttle position as follows:
Engine Speed Ported Manifold (full)
Idle None Maximum- about 17-20" Hg normally.
Part throttle Some - varies w/load, speed Some, varies w/ load, speed. Not necessarily same # as "ported"
Full throttle Very little Very little

Manifold vacuum is the vacuum created by all pistons attempting to suck air thru a more or less closed off intake. Whereas... "ported" vacuum is created by a tiny port in the edge of the Venturi, just above the throttle plate when it is [nearly] closed for idle. Thus ported vacuum may be a different value than manifold vacuum. BTW, that's why at idle there is virtually -no- ported vacuum- because the port is situated just above the throttle plate, where there is at that time approximately atmospheric pressure which is approximately 0 vacuum.

"Ports" or nipples on carb can provide either full manifold vacuum or "ported" depending on where they lead to/ come from. easy to check. Just apply the finger test or the gage test at idle, then at part throttle.

Check your source by disconnecting the hose from your canister and check for vacuum at idle (hold your thumb over the end or use a gauge). If there is vacuum at idle it's a full time source. A manifold vacuum source doesn't necessarily have to be on the manifold itself; it could be a full time port on your carb. However, a ported vacuum source will either be on the carb or originate from the carb.

As for ported vs manifold vacuum, definately go with ported for vacuum advance. Ported will give you no advance at idle but will increase the advance as the throttle is opened. Sometimes with manifold you will get a slight sputter or bog when the vacuum advance drops out as the throttle is suuddenly opened. Experiment to find what works best for driving under normal driving conditions (spark plug color, fuel mileage, and response). Spark plugs can be tuned by setting the gap at .040 then opening the gap .005 at a time until the car slows down, engine starts missing, or gas mileage suffers. Then close up the gap to the last setting.

The whole thing about vacuum advance is drivability and fuel economy and it doesn't hurt performance so let it be. Where you will gain more performance is by recurving your distributor. It dials in greater ignition advance, which is necessary when you've got a thin or lean air-fuel mixture such as at part-throttle; you have to start that mixture burning quite early in order to get all that fuel combusted by the time the piston is passing TDC.

It greatly improves part-throttle fuel-economy. You can disable it temporarily with a golf-tee plugging the line to the canister. It also bumps your idle speed up. That's it. Makes little to no difference for actual driving, only for idle emissions quality. If you didn't disconnect the vacuum advance when setting the timing, it is probably bumping up your advance as you hit third gear, since your vacuum starts to come up as you approach top speed.

On any Oldsmobile V-8 engine, the distributer gets ported vacuum. You don't want advance at an idle, you want it when crusing. Why do you think they call it "vacuum advance"? Because when the engine is above idle, vacuum pulls the points or magneto around in the distributer, advancing the timing.

No matter what brand carb you have, the distributer never gets manifold vacuum. Even though a very, very few olds' came from the factory with manifold vacuum. The only reason they did this is because when they put in the distributers, if the timing would not advance enough, they used manifold vacuum. This was easier than pulling the distributer and realigning it.

DO NOT USE FULL MANIFOLD VACUUM to the dist'r unless your shop manual calls for that setup- I understand some later [late 70's?] Oldses did that. Not in '68 for sure.

Here's an example (hypothetical): say the spark plug fires at an idle with the piston 7/8 the way to the top. As engine speed increases, the spark needs to leave the distributer cap sooner because the fuel will take the same amount of time to burn as at idle, but that will put the maximum force of the burning fuel acting on the piston too late during the power cycle. If the spark timing is advanced, the maximum power acting against the piston is advanced as well.

Now relate this to an Olds engine. Take off the distributer cap and look at the internals. Make a rough sketch of how they function, especially the vacuum advance. Think of how much advance there should be at different rpm's. At 1000, rpm the amount of vacuum should/will be minimal, hence the timing advance is minimal. Now at 5000 rpm, the amount of vacuum should/will be full, hence the timing advance is full. As a final note "the distributer gets ported of timed vacuum, not manifold vacuum".

With manifold vacuum, the timing will be advanced at an idle, and when accelerating the timing will retard. Then when at a cruising speed the timing advances. this final advance will not exceed the initial timing at idle. Giving you about 8° final timing compared to 28° with ported vacuum.

If you have a long duration camshaft, you might have to run full manifold vacuum according to the Edelbrock manual for their RPM carbs. The url for their online manual is: http://www.edelbrock.com/automotive/eps_sect2.html#ref

They don't tell you what is considered "long duration" though. The installation instructions that came with my carb, very specifically stated to use the full manifold vacuum port on the carb if the vehicle did not have EGR. For EGR equipped cars, they specified the ported vacuum port on the carb.

I followed the instructions and used the manifold vacuum port and the car runs fine. I'm running about 36° of total vacuum (set with the advance disconnected) and I did recurve the distributor using an adjustable timing light. I also didn't worry too much about inital advance and calibrated for total advance.

[ Thanks to Mick Gillespie, Chris Witt, Dave Dillon, Bob Barry for this information. ]

Vacuum Control Switches:
A good explanation can be found at http://www.crosswinds.net/~smithtp/olds/LaunchPad.htm.

[ Thanks to Thomas Smith for this information. ]

Recurving Results:
I recurved my HEI this weekend and wanted to let everyone know what a mileage increase I got out of it. My original '70 350 is running 10.25:1 compression, so I have never been able to run to the proper initial timing (It pings in this hot Texas sun) At 90MPH with the A/C on, my car averaged about 12.3 MPG (I have 2.56 rearend) I always thought that was a bit low and seemed that it took more pedal than should be necessary to keep it going. After the advance kit, I jumped to 19.53 MPG at the same speed with the A/C, and it cut my pedal usage in half. The advance kit is something that most of us have heard about at one time or another, but often dismiss it as a gimmick. An $8 part is saving me $$$$. Note: This result is by and far the largest gain I've heard. Typical is around nothing to 1 MPG. Conversion from a badly tuned and maintained points ignition to a tuned HEI system could get you this much increase.

I run an HEI w/MSD box and vac advance hooked up to ported vacuum, and run 22° initial w/o vacuum advance with 35° total advance. Mechanical advance is 13°. With the vacuum advance hooked up, timing jumps to over 40°. I've never had a problem with detination or spark knock. Engine is .030" over 455 at 9.89:1 compression. Big cam and 3000 RPM stall converter.

[ Thanks to Rob Thomas for this information. ]

Advance Troubleshooting:
The distributor's curve and the vacuum advance doesn't match up since you say that during light acceleration on the highway you get pinging, but not at WOT. To verify that the vacuum advance is causing the ping disconnect it and plug the vacuum line then try to get it to ping on the highway. If it doesn't do it fine, but if it still does it I would gravitate towards thinking that it is pinging some at WOT but you may not be able to hear it due to other noises (like a loud exhaust).

A high compression engine is very sensitive to initial timing settings. Too much initial and they tend to be hard to crank when hot. An old trick is to set the mechanical advance springs in the distributor very weak so that at idle the advance is partially open. That way when cranking your timing is closer to 0 than when at idle. Another possibility is that the starter could be getting too hot. An easy way to tell if the timing is the problem is to pull the coil wire. If it's still hard to crank then it's either a starter/cable problem or simply a tight motor as Paul said.

First, what type of fuel are you using? If your using Premium unleaded your curve seems to be a bit steep. Back off to 15° initial, 32° total, and see what happens. Keep in mind that the hotter the engine gets the more prone it will be to detonate. The only thing to do is to play with your curve to see where the problem is. It seems to me, on the info given, that you have too much timing coming in too quick. You're right that part throttle detonation can be caused by amount of vacuum advance (not always though), but you have a lot of advance coming in at relatively low rpm's. I would try to stretch the curve out over a few more RPMs, and also note what RPM's you're getting the detonation at. Try using your "slope" adjustment to make the curve angle somewhat more "shallow". Distributor curves are a bit of a black art and the timing computer is a nice piece, but it does nothing more than make the black art of curve a bit easier to work with.

[ Thanks to Mike Bloomer, others below for this information. ]
[ Thanks to Chris Witt, Fernando Proietto, Pat Clark, Andrew Green, Bob Handren, Tom Lentz, Greg Pruett, Bob Barry, Joe Padavano, Graham Stewart, Scott Kozhill, Scott Mullen, Kevin Wong, Chris Fair, Erik Nowacki, Chris Ruper, Mark Prince, Rich Inacker, Todd Morris, Kurt Heinrich, Jeff Easton, Mike Frederick, Ron Forsee, Mike Bloomer for this information ]

Cap and Rotor Indexing

Indexing involves relocating the tab that keeps the distributor cap in one place. What I think it takes to accomplish it is cutting a hole in the side of a distributor cap, under the #1 terminal. The cap is marked with the location of the inside terminal (on the outside) and the rotor is marked with the location of the rotor tip below it's location on the rotor's side, so you can see it inside the hole of the cap.

You start the engine and connect a timing light on #1 plug and shine it on the distributor. This will tell you exactly where the plug is fired in relation to the cap. From there, you can fill and relocate the cut in the side of the distributor's base if it's really off. I remember hearing of this in a stock car racing magazine and they said it also pays to be careful where you buy your distributor caps, since they also can be mis-indexed.

Is it worth it? I don't know, but if you always buy your caps from the same make and place, they should be accurate to each other. If you did this and did find that the cap wasn't indexed properly, you could either fix the distributor or replace it. We here at the race team are going to be real careful about who and where we buy our caps and make a fixture to check them this winter, and index our distributors exactly alike so there won't be any variance in timing.

What's being done is making sure that the rotor references the proper place in the cap. In some applications, the locating notch on the distributor's not exactly where it should be.

The number of degrees that the cap terminals and rotor are off can't be changed by rotating the distributor a few degrees. That would also change the overall timing, advancing or retarding. Since the point plate (or reluctor [HEI]) also moves when you move the distributor, the timing would change as you move the distributor. What you are trying to do by indexing is make sure when the points or reluctor tell the coil (to fire) the rotor is positioned at the optimum position in relation to the terminal inside the cap. There is an entire science in racing that looks into things like where the best relation between the rotor and cap is for transmitting the energy that eventually sparks at the plug. It has to do with those ten- thousandths of a second differences in lap times or 1/4-mile ET's.

I must repeat, I'm no expert at this, I'm only relating what I remember reading in a racing publication some time ago.

[ Thanks to Ken Snyder for this information. ]

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