Picking the Best Big Block
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Big Block Advantages
Anything a small block can do, a Big Block can do at less RPM and with less
dollars, and chance of breaking something.
The additional weight of a Big Block, compared to a small block, is marginal, around 50-70 lbs.
No small block can match a Big Block's torque output.
Isn't Bigger always better?
The small block
rebuttal.
[ Thanks to
for this information ]
What Should I Look For in a BB For My Performance Olds?
That depends a lot on whether you are going to fully rebuild your engine-buy
new pistons, have it bored, all that. If you are buying new pistons, then
just about any serviceable block will do, and what you are really looking
for is the best serviceable heads and crankshaft for your money, with the
crank and rods compatible with your desires: 425 CID vs. 455.
While there's "no replacement for displacement,"
you should be aware that all 425's have forged cranks, whereas 99.9% of
all 455's have cast cranks. Both have the same bore; the main difference
is the internals: the stroke, rod length, piston compression height combination.
Some folks prefer the stronger crank and shorter stroke of the 425 engine,
even if it is 30 CID smaller. You can swap the internal reciprocating assembly,
to make either a 425 or a 455 out of either block. However, most 425 blocks
have the older style cam bank angle, which makes cam selection a bit more
difficult, and the other 425 blocks use the larger lifters, which cost
more.
Then again, the early 400 is a high revving engine, although 25 CID less than
the 425. The late 400 is a very long stroke engine for it's bore. A good street
engine, but not the best track engine.
Comparing the 67 400 with the 68: The '67 400 cid 442 motor had 440 lbs.ft
at 350 horses. The '68 400 cid 442 motor had 435 lbs.ft at 350 horses.
I don't believe the last torque numbers for the simple reason that the
'68-'69 motors were dogs at the track. Great street motors but they just
don't rev like the short stroke motors. Anyway, those are the "factory"
numbers. On the track the '68-'69's weren't as good.
Some see the 425 as definetely the better choice for high RPM applications
(The early 400 fits in here as well).
The engine is over-square, meaning the bore is bigger than the stroke,
which usually always means higher revving than an engine which is (bet
you guessed what's coming next) under-square as is the 455 - bore
smaller than stroke. Not to mention the forged crank in the 425. The late
400 is not a good choice for a high revving application.
If you plan to use the engine 'as is', or just do a simple cylinder hone,
ring/bearing overhaul, then you'll be looking for a pre-71 engine, as they
had compression of about either 10.2 or 9.0. Quick ID tip: pre-71 engines
had heads with casting ID "F" or earlier at the lower left corner
of the head. Engines with G, Ga, or J heads were low compression- about
8.2:1 at best. Generally, C-head engines are best.
A Toro oil pan is a cheap way to increase your oil
capacity. It will hang an inch or so below the A-body frame so it is a
little more exposed to danger. If you have headers they will usually
be sacrificed to the pavement/parking stop gods first.
If it were my engine I would buy a new oil pump. The key thing to remember is
that the Toro pan is deeper so you need a Toro pickup. The Toro oiling
system also includes a crank scraper on the side of the pan, a baffle/crank
scraper above the oil pump and a skimmer for the timing chain. All this
keeps the oil where it belongs and even adds a few hp by making everything
lighter (since it isn't slinging oil around). You need the whole setup which
includes all these goodies and the main bearing cap bolts with the studs
incorporated so it can all be put together.
Most of the 425's have the 45 degree
lifter angle with .842" diameter lifters. The Toro blocks have a 39°
lifter angle and .921" diameter lifters. The 1967 425's have the 39
° lifter angle and .842" diameter lifters.
FYI, a bigger lifter diameter lifter acts more like a roller lifter. This
is what led to mushroom cams in NASCAR.
Just a note, the .921" lifters are much more expensive than the more common
.842" diameter lifters.
For pistons, TRW does not make a forged piston for the 425. However, Speed-Pro
lists one. I ordered a set of the Speed Pros, and after being on back order
for 3 months I had to cancel my order. I found a guy with a set of JE piston
for a 425 for at a very reasonable price.
I called ARP for a set of rod bolts and they informed me there are two
different bolts used in the 425 rods. There suggestion was that I bring one
of the rods in so they could match it to my connecting rod. I also picked
up main studs with windage tray standoffs for
a 460 Ford for my Olds. According to the guys at ARP they feel it fits
better than the stud they sell to Mondello for the Olds motors.
The flywheel bolt pattern is different between the pre 1968 and 1968 and
later engines. My
car is a manual trans and it took a bit of digging to locate a manual trans
flywheel. Just be sure to get a matching flywheel when you get the engine.
In general, for a given displacment,
- A larger bore x shorter stroke will make an engine that is easier to
operate at higher RPM, and produces greater HP.
- A smaller bore x longer stroke will make an engine that runs at
lower RPM, and produces greater torque.
So, as an over simplification,
bore = hp
stroke = torque
HP is the mechanism that lifts a 550 pound weight at the rate of 1 foot/sec.
Torque is the mechanism that keeps the engine turning when a load is applied.
They both have value. In engines as close as the Olds 425 & 455 the size
numbers are fairly similar, so the results of building either will be
similar. The 455 is about 10% greater displacment, so theoretically
it should yield about
10% greater HP, everything else remaining constant. You gain the
displacment by increasing stroke, so the torque aspects of the 455 should be
superior. On the other hand, you could get equal HP out of the 425 by turning it
faster (part of the value of a shorter stroke), but shorter stroke yields
less torque, everything else remaining the same.
455's have been used extensively for high output engine building. They are
certainly more obtainable than 425s, and they seem to live fairly well, so
that the benefits of a steel crank may, in fact, be fleeting. The greater
displacment has value, and obtainability does too, in terms of initial cost.
If you've got a 425 build it, it should do very nicely, if you've got to buy
the core motor then buy a 455 as it will cost less as a core, and should not
cost more to build.
For anything other than an all-out high RPM drag
motor, I'd stick with the 455. They're significantly more plentiful,
parts are more readily available (yes, I know the majority are common,
but for those that aren't...), and you don't get into the 39 degree vs
45 degree vs 0.842 vs 0.921 maze of confusion. A nodular crank, or
even a properly prepared cast crank, will take anything you can
reasonabley dish out, especially for what it appears will be a daily
driver. Yes, the forged crank is nice, but probably not as necessary
in your application as the extra cubic inches. (Come on, you expected
me to say anything but that?)
[ Thanks to Chris Witt, Bob Handren, Ron Forsee, Cliff Feiler, Joe Padavano
for this information ]
Big Block Factory Performance
Here's the engine comparison for the 442 and SX:
source is Olds 442 and W-machines Restoration Guide
(reprinted from service manual).
- The W33 was optional on all 88's.
- The W32 was std in 442, optional on Cutlass Supreme.
- The L31 was available as an option in the Vista Cruiser
(where it was fitted with dual exhaust), optional on
all 88's (with single exh) and std on 98 (single exh).
- The L33 was optional on Cutlass Supreme, Cutlass S,
Cutlass sedans and wagons (presumably other than vista)
and std in SX (for awhile)
I think we've already established that the same carb
was on W-33 as well as AT 442's. Could these two
motors really be identical? Are the 442 and W-30 pistons
any different from the others, presumably dished?
And whats up with the L31? Lower compression and single
exhaust yeilds same hp at lower rpms, better torque again at
lower rpms, than the 442. Should I not be racing vista cruisers
at stop lights? :-)
Jeff easton
Why Get a Toronado Engine?
Toronado engines were generally the cream of the crop; equivalent [or
very nearly] to the 442 and W-30 engines, yet often priced the same as more common
and lesser quality engines in the junkyards. Equipped with the best parts-
aluminized valves, closer tolerances, etc.
For instance:
- Big valve heads, thru 1971 anyway.
- Highest compression pistons.
- Oil deflectors ['windage trays'] were used thru 1972 or so.
- Deeper oil pan holds an extra quart.
Drawbacks to a Toronado engine: The oil filter mount will not fit other
bodies; easy to change. The dipstick is slightly different in markings:
the Full mark is the same, but the Add mark is about ¼" lower. Exhaust
manifolds are not useful for any other application.
[ Thanks to Chris Witt for this information ]
How to Tell If It's a Toronado Engine
Several clues are built in to identify a Toronado engine. If it's in
a Toronado engine bay, that's a good indication. Toro's usually have a
very lo-rise intake manifold; the carb appears sunk in about an inch below
the normal position. If it's a pre 1968 engine, the engine ID stamped into
the front of the RH cylinder head will tell. The Toro oil pan has a unique
shape- it's narrower side to side in the sump area, an inch taller, and
there's a clearance 'dent' just in front of the sump, where the RH drive
axle passes under the engine. Also, the oil filter mount is angled quite
forward, and one of the attaching bolts is quite long [about 3"].
Other evidence would be exhaust manifolds, if still attached, likely
to have a letter code from the early alphabet, like D, H, G, J... and will
point more up and out than a typical A-C bodied car would have room for.
There might still be a motor mount attached to the timing cover, behind
the harmonic damper. If the heads are off, say, for inspection before sale,
measure the intake valves. That's what you are really after, anyhow. If
the pan is off, check for the Toro windage trays on the front main cap
and on the #4-5 main cap, as well as the crank scraper which runs down
the RH side of the oil pan.
[ Thanks to Chris Witt for this information ]
Summary of Olds 400/425/455 Engines
You wish:
0- Exotic heads: D, F, H, or maybe K. Block? Crank? If the price is right,
who cares!?
Earlier blocks have higher nickel content, which makes them
harder and which makes them wear less, though I've yet to hear of someone
tearing up the mains or cylinders on a later 455 block. For all intents and
purposes, a street 455 will do just fine with any well-prepared block. In
fact, I'd say a well-prepared '76 block would fare better than a
poorly-prepared '68 block. Early (68 - 70ish) blocks are probably best.
Look for a large raised "F", or "F0" through "F2" on the rear (flywheel
end) face of the block. Bottom line: get the approximate year of manufacture
from the letter ID, and use the earlier is better line of thinking.
Best of the best:
- Toro/442 engine 1968-69. Big valve C heads. 4V carb. High compression.
Toro engine has oil pan with extra capacity, built-in crank scraper, factory
windage trays. The best heads, crank, block, etc. Best-flow C heads, will
need hard seats installed for the exhaust valves. Small, inexpensive lifters
on the most common bank angle.
- Toro/442 engine 1970-71. Big valve E or G heads. 4V carb. Same benefits
as above, plus hard seats. Generally equivalent to or better than the comparable
442 engine. 1971 G-head engine was much lower compression than previous
years due to deeply dished pistons. Points off: C heads are said to flow
best.
Best, easier to find:
- Toro/442 engine, 1967. Big valve C heads, all the usual Toro goodies.
4V carb. Will need hard exhaust seats. Some racers favor the Toro D block's
large lifters, with the modern 39 degree cam bank angle, because the large
lifters seem to tolerate high cam lift better. 400 CID E-block 442 engines
are very rare, easily tradeable for a nice 455.
Slight drawback: 425 internals [or, is that forged crank and short stroke
a bonus?], requires the early pattern flexplate, and those 0.921"
lifters at $100 a set or so, which require shorter pushrods. Also, since
no Toronados were MT cars, if you are using a manual trans, you will need
to have the crank drilled for a pilot bearing. But, then, that applies
to almost all Olds engines as well. If you'd rather have big valve heads
and a forged crank than 30-55 more cubes, this is the engine for you. If
you'd prefer cubic inches, but can't find the best, or the next best . . .
-
Any [i.e., non-Toro] 1968 to 1969 455/400 is probably the easiest to find.
Common in 88, 98, wagons. Will have C heads, probably not big valves. Engines
in Vista Cruiser wagons may be the rare G-block 400 [serviceable as a 442
engine] and may have 'notched' rocker arm covers and/or dual-exhaust manifolds
useful on a Cutlass/442. Of course, a 4-barrel engine is preferred over
a 2-barrel, but if you are buying an aftermarket intake and new pistons,
that point is moot, except that you can sell a 4V intake and carb more
easily.
-
1967 425 engine. Common in 88, 98, wagons? "Best flowing"
C heads, though not as good as big valve C's. Forged crank. Drawbacks:
Non-Toronado 425 D-blocks with 0.842" lifters will have the older
45-degree cam bank angle; cam selection will depend on this feature.
-
The
usual 425 vs 455 tradeoff: you will need to either
A) build a 425 forged-crank
engine with these parts, or
B) find a 455 or 1968 to 1969 G-400 engine to donate
the crank and rods, then get 455 pistons. 425 pistons are not fungible
with 455 pistons due to a different distance from pin center to top of piston
("compression height").
Good:
- 1966 Toro/442 engine. B heads. Identical in benefits and drawbacks
to the 1967 Toro engine [#3 above] except that the 1967's C heads are said
to flow best.
- Any other pre-72 [head up thru G, but not Ga castings] 400, 425 or
455. Run of the mill engines such as a 2V carb would likely have low compression,
small valves, no windage trays, etc., all of which can be altered during
a rebuild, for some cost. If it's a D-block 425, watch out for the small
lifter/early cam bank angle combination.
Darn near adequate:
- 1973-up smogger 455's with J heads, they did NOT have big valve heads,
'73-up units may not even have the 'oil deflectors' or 'windage trays' that
earlier models had, and the compression ratio is very low,
like 8.5:1. If you buy high compression pistons,
have larger valves fitted, buy a nodular crankshaft, an aftermarket or
pre-EGR intake, and a windage tray, you'll have a motor that's almost respectable.
But, it'd still have J heads with that tiny exhaust port. Why bother? Avoid,
unless there are no alternatives.
OTOH, a regular 455 shortblock is pretty stout, even with stock pieces. If
you do a set of good heads and use your own cam, starting out with a
"crate" shortblock might be a viable option, as you can probably pick one
up for less than the cost of machine work alone on a junkyard 455. Just
don't spin it past 5000rpm!
OTOH, OTOH, if you picked up one of those few NOS crate W-30 shortblocks
that Berejik has stashed away in his parts dept, then you'd have a pretty
good engine to start with, I'd say... ;)
[ Thanks to Chris Witt, Bob Barry for this information ]
![[ Notice: ]](hand_rig.gif)
Please refer to the
Blocks section as well!
Please refer to the
Heads section as well!
Please refer to the
Cranks section as well!
Please refer to the
400 CID Engine detail section as well!
Please refer to the
425 CID Engine detail section as well!
Please refer to the
455 CID Engine detail section as well!
Obtaining Your BB Engine
Running Vehicle
You're probably always better off starting with a motor that runs,
just because you can see what you're getting into. Plus, you can be
reasonably sure that there aren't any fatal flaws lurking in a
rebuild. Certainly just pulling a running engine and dropping it in
is the cheapest route in the short run, but you obviously still have a
used engine. Cheapest in the long run is probably rebuilding it now -
just watch the mightaswells (eg. mightaswell put in the big valves while
I'm having the heads done...).
I actually came across an ad the other day for a "455 Rocket plus trans,
strong, low mileage, drive car come. $500". Drive car home. Sounds like
it comes with the whole car. Great deal, esp. if the year is pre-'73.
Especially if the year is 1968-9.
I like to buy engines for under $100, but depending on condition, running
or not, $200, $300 and up. If it is running, perform a vacuum guage analysis
to see what condition it is in.
Parts Yard Engine
Since you're rebuilding it, you know what you're putting into
it. Big drawback is getting the engine home, and finding a couple rods have
been "blue'd" (spun a bearing so bad that the metal overheated and turned
blue), in which case you need a new crank and some rods.
Crate Engine
Depends whose crate it comes in. A standard rebuilt 455 over the counter at
Pep-Boys or the like,
will have the cheapest parts that are just good enough not to blow
up on enough engines that rebuilding them is profitable. Usually all
low-compression, and often used later blocks, smogger J-heads, and
low-performance cam (it's intended to cover a variety of applications, so
they build them for the lowest common denominator). This is the worst
scenario for a performance engine.
If you find a crate 455, please, PLEASE, let us know where.
Unfortunately, I don't think they exist (at least not from GM). You
can certainly buy kits from PAW et al, or complete motors from
Mondello, Miller, and Smith. This last route unfortunately is a long
way from low buck.
[ Thanks to Chris Witt, Bob Barry, Joe Padavano
for this information. ]
Table of Contents •
Index •
Acknowledgements
History •
Engines •
Blocks •
Heads •
Cranks •
Intakes •
Exhaust •
Pistons
Transmissions •
Diffs •
Brakes •
Suspension •
Steering •
Cams •
Carbs •
Interchange
Best BB •
Best SB •
260 •
303 •
307 •
324 •
330 •
350 •
371 •
394 •
400 •
403 •
425 •
455 •
Diesel
Rebuilding •
Buildup •
Swap •
Restore •
Option Codes •
Wheels •
Ignition •
Comp Ratio
The W's •
The H/O's •
The 442's •
Toronado •
88 / 98 / Starfire •
Cutlass •
Jetfire •
Wagons
Basic Tech •
How To •
Miscell •
All Vehicles •
Additional Information
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