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,

  1. A larger bore x shorter stroke will make an engine that is easier to operate at higher RPM, and produces greater HP.
  2. 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).

Engine 390hp 370hp 365hp 365hp 320hp
[email protected] [email protected] [email protected] [email protected] [email protected] [email protected]
[email protected] [email protected] [email protected] [email protected] [email protected] [email protected]
Comp. ratio 10.25-1 10.50-1 10.50-1 10.25-1 10.25-1
Carb 4bbl 4bbl 4bbl 4bbl 4bbl
Exhaust dual dual dual single dual
Cars W33 W-30 W32 L31 L33

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:

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:

Best, easier to find:


Darn near adequate:

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: ]Please refer to the Blocks section as well!
[ Notice: ]Please refer to the Heads section as well!
[ Notice: ]Please refer to the Cranks section as well!

[ Notice: ]Please refer to the 400 CID Engine detail section as well!
[ Notice: ]Please refer to the 425 CID Engine detail section as well!
[ Notice: ]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. ]

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