Definition - Big Block vs Small Block

[Rory Riedy]

All,

You may think I am crazy, but is there a formal definition of a big block vs a small block. I am not asking simply from a corvette standpoint but all cars. Is it a physical dimension (cubic inch, displacement, etc.)? I watched a show this weekend & it said the new vette's 7.0, 427 cubic inch engine was the largest small block ever manufactured by GM. I tivo'd it so I'm sure I hear it right. What am I missing? Was the program in error? How can they call the new engine a small block?

When I asked this around all I got was "I never really thought about it? I don't really know now that you bring it up."

Anyone got a good answer?

Thanks

Rory

[Tim G.]

Re: Definition - Big Block vs Small Block

Hemming Musclecar Magazine had a good article/opinion on this recently. The topic certainly creates lots of confusion. The bottom line it that there is no clear answer on what is a big block and what is a small block. Sure the 427 of the 60's and 454 of the 70's were big blocks, but what about the 396 big block and the 400 small block? Why did Chevrolet offer a 400 small block and a 396 big block?
It is just as confusing with Ford big block and small block engines. Pontiac used the same blocks with different internals to differentiate big and small blocks. The answer is all over the board.
I am pretty sure my '67 427 is a big block, though. At least I hope it is.

[Joe L.]

Re: Definition - Big Block vs Small Block

Rory-----

I don't know if there is a precise definition of the term "big block". There have been 2 "families" of Chevrolet V-8 engines produced since 1955. One "family" is known as the "small block" and the other family is known as the "big block". The physical dimensions of the big block engine family is generally larger than the similar dimensions of the small block engine family. Here's a breakdown of the various members of each engine family:

SMALL BLOCK

Generation I 1955---present; produced in 262, 265, 283, 302, 305, 307, 327, 350, and 400 cid displacement. Also produced in 383 cid displacement for SERVICE only. This series engine was used in all 1955-1991 Corvettes with small block engine;

Generation II 1992-1997; produced in 4.3L and 5.7L displacements; this engine was used for all 1992-1996 Corvette LT1 and LT4. It was laso used in 93-97 Camaros and about 94-96 Caprices.

Generation III 1997--present; produced in 4.8L, 5.3L, 5.7L, 6.0L, and 7.0L (2006 Z-06) displacements. First used for 1997 Corvette; most versions are all aluminum with the exception of some truck 6.0L

Generation IV 2005--present; updated version of the Gen III; has variable valve timing and displacement on demand; produced in 5.3L and 6.0L cid.

BIG BLOCKS

Mark I----1958-1965; produced in 348 and 409 cid displacements; never used in a Corvette;

Mark II----"cross" between Mark I and Mark IV; 427 cid "mystery engine"; VERY few produced. Never installed in a production passenger car;

Mark III----never produced

Mark IV----produced 1965-1991; produced in 366 (truck), 396, 402, 427, and 454 cid displacements. This is the engine used in all Corvette "big blocks" manufactured from 1965 through 1974; mostly cast iron block and heads with exceptions of 1967-69 Corvette with L-89 and L-88 (aluminum heads), 1971 Corvette LS-6 (aluminum heads) and 1969 Corvette/Camaro ZL-1 (all aluminum)

Mark V (aka Gen V)-----1992 to 1995; updated version of Mark IV; same, basic dimensions; produced in 454 and 502 cid; one piece rear seal and net lash rockers; not used in any PRODUCTION passenger cars; truck, marine and SERVICE use only; all cast iron for PRODUCTION;

Mark VI (aka Gen VI)---1996--present; further updated version of Mark V; produced in 454, 502 for PRODUCTION; some larger cid for SERVICE only; has roller lifters and revised timing cover; all cast iron for PRODUCTION;

Gen VII (aka 8.1L)----2002--present; 496 cid engine; used for truck and marine applications; same basic dimesnions as earlier Mark-series engines. All cast iron for PRODUCTION,

[lyndon sharpton]

Re: Definition - Big Block vs Small Block

an what about the 572, what is that block based on?

[Mark #28455]

Re: Definition - Big Block vs Small Block

gen VI block, bored 4.56 with a 4.375 stroke as sold by GM.
Aftermarket commonly uses 4.5 bore and 4.5 stroke.
Mark

[Geoff C.]

generally, a SB is a starter motor for a BB *NM*

[Joe L.]

Re: Definition - Big Block vs Small Block

lyndon-----

572 cid is a SERVICE-only configuration. It is built on a Mark VI TALL DECK BLOCK. Tall deck blocks are, primarily, designed for heavy duty truck applications.

[Duke W.]

It's real simple...

...all small block Chevrolet V-8s from the first in model year 1955 to the current LS7 have 4.400" bore centers and OE displacements ranging from 262 CI in the mid seventies to 428 CI in the new LS7.

The key parameter is bore center.

I don't think there is any such distinction for BOP and Cadillac. IIRC their last division built V-8s were the same bore center as their first OHV V-8s that were introduced in the forties and fifties. Chevrolet was the only division that had more than one V-8 engine architecture, and the primary reason for "big blocks" was that Chevrolet built medium duty trucks that needed more displacement than was available in the small block. But it was natural that the W-block truck engine migrated to passenger cars as the "performance wars" escalated in the fifties, and, no doubt, the Mark IV was designed with an eye on passenger car performance applications in addition to replacing the W-block in trucks.

Duke

[Jim W.]

And a BB is for marine applications(anchor) ;-) *NM*

[Warren F.]

Re: Definition - Big Block vs Small Block

Rory;

My belief is that because there are two different physical engine sizes, most people refer to the terms big block / small block. This doesn't seem to be the same case with engines in the Buick, Pontiac, Oldsmobile divisions. I personally can't tell any physical difference, when I look at a 400cid Pontiac from a 326cid motor, or a Oldsmobile 455cid from a 350cid engine, but there sure is a difference when viewing a 396, 427, 454 engine from a 326, 350 engine in Chevrolets.

[Mark H.]

Re: Definition - Big Block vs Small Block

What about the LT5? Gen I with fancy heads (& lots of other goodies)?

[Duke W.]

Look at the bore center... *NM*

[Grant M.]

Re: Definition - Big Block vs Small Block

Perhaps for reasons of the "bore center" that Duke refers to, Pontiac's 350 CID of the mid-seventies was considered a "big block", as was the 400 and 455 of the same timeframe. I can't speak to the 326, but it might very well have also been a "big block" by some parameter. Incidentally, a 1975 Pontiac 350 with identical caburetion (Rochester 2-barrel) and exhaust (single back to muffler and dual tail-pipes) was rated at 155 SAE net HP versus a 1975 Chevy 350 at 145 SAE net. Was the difference owing to bore/stroke?

grant

[Duke W.]

Re: Definition - Big Block vs Small Block

The original Pontiac V-8 from 1955 was 370 CID, then later offered in various displacements from 326 to 455 CID, but they were all the same bore center/architecture, so there is no "small block/big block" distinction.

Same with Buick, Olds, and Cadillac V-8s as I said before. The original Cadillac OHV V-8 from 1949 (my dad had a '49 Fleetwood) was 346 CID IIRC and grew to 500 - don't remember all the original displacements for Olds and Buick, but those V-8s grew to 455 CID. All could probably be considered "big blocks" because they had bore centers and deck heights that allowed them to be expanded to "big block" displacements. The Pontiac 326-350 could be considered a "big block" with a "small block" displacement. The current LS7 is a "small block" with "big block" displacement, but at 4.125" by 4.000" I doubt if it can be expanded any further given the 4.4" bore center and 9.025" deck height.

The minor difference in power between the Pontiac and Chevrolet 350s you refer to is probably buried in some combination of internal design details and the inlet and exhaust system configurations, which must be included in the SAE net rating, but there is no one parameter that makes the difference.

Duke

[Mike M.]

Re: Definition - Big Block vs Small Block

Duke: i think the first ohv caddy displacement was 331 ci. the old rockets started as 303 ci, grew to 324, then 371, and finally 394 in 1964. by 1965, olds cast a new block that started as 425 ci and grew to 455 ci.regards, mike