jost6453

What's the techincal diff between a 'small block' vs 'big block' engine? I was asked by some buddies but didn't have a great answer, other than physical size. Is the C6 Z06 a 427 small block?

toddalin

Typically, as in the case of the Chevys, Fords, and Chryslers, it's based on the bore spacing. But that doesn't apply to all makes. For example Pontiac used the same block for the 326 to the (IIRC) 455 CI engines.

cwis9992

i believe journal size is involved as well. im not exactly 100% on that but im pretty sure of it

cardo0

That's a very good answer.

If you look in the GMPP catalog they have all their small and big blocks listed by part numbers in their own respective section so it makes fairly easy. But the LSX motors have no big or small block labels - only LSX blocks whether 260 or 427 cubes.
U can stroke and bore a small block to well over 400 c.i. but it is still a small block regardless. Only the marketing employees at GM know why they call anything what they do.

cardo0

Ben Lurkin

The big block chevy is physically and dimentially a much larger engine than the small block. Take a look at them side by side and there's no question which is which and why. The BBC can be had in sizes over 700 cubic inches.



The lsx series is the third & fourth generation of the small block chevy. As mentioned above, they share the same 4.40" bore spacing.

RobRace10

Guess which one is the 427 and which is the 350.

NateReyes1986

Nice, I'm a visual person so the side-by-side is definitely working for me.

toddalin

Actually, from this perspective, the reason that the big block looks big is not the block at all, but the splayed valve heads used on Chevy big blocks as opposed to the in-line valves used on Chevy small blocks.

If you were to look at a 4-valve small block, or even a splayed or opposing valve head such as a Ford Cleveland of Chrysler hemi, you would be hard pressed to see this difference from this angle.

RobbSalzmann

Nice pic!

FWIW, my 427 looks just like the one on the left.

Don 79 TA

one of the old tricks i was taught from the engine shops back in the day was valve cover bolts, meaing BBC had more then the SBC
how this "theory" applied to other makes.... dunno
of course this was back in the early 80s when i heard this, quiet honestly heard it referenced like that alot too

since i'm a pontiac fan, you can always tell a non-pontiac person makes an add when they describe a pontiac motor as a Big Block
sure it's big in size, but basically dimensionally all the same so technically there was no small or big block pontiac

from what i remember, it was used in reference to it's CI's
meaning most small block motors were typically 350's and under, over used to be classified as big
however you can now get 450+ cubes in a small block dimensions, so again kindda throws that out

jasper711

The terms "big block" and "small block" are predominately in reference to classic Chevy's. There are also large and small classic Mopars. There is no big block or small block Pontiac as they all share external dimensions, the definition gets murky with Olds and Buick as it becomes a matter of deck height, and Ford really muddied the water with old Y blocks, the small block, FE's (which are sort of smallish by big block standards, but generally referred to as big block), MEL's (the biggest block available when FE's were made), Cleveland family (which I've heard rednecks refer to as "big block 351's") and then the largest 385 series; none compatible with each other.

All of these designations are somewhat obsolete on new cars and in any case the designation is no better than the person speaking it. But a big block Chevy will always be 396-402-427-454 etc., and a small block Chevy is usually 265-283-302-305-307-327-350-400

randyredleg

To really confuse things,the 348 was a big block (also used for a 409/427)

cv67

So was the 366

ManiM1191

awesome thread! great explanations and pic on here! thanks!