What defines big block vs. small block?

[70camaro_someday]

This is probably a very basic question but, what defines an engine as a big block or a small block? I've seen engines be a small block when they are 403 c.i. (Olds 403), and I've seen engines be a big block while only being 400 c.i. (Pontiac 400). What are the "requirements" to be a big block??

[Mwilson]

stroke to bore ratio? how many people it takes to lift one?

[This message has been edited by Mwilson (edited January 16, 2005).]

[gregh]

Buick, Olds & Pontiac engines were only made in one basic "size", there is no external difference between a 350 & a 455cid.
Chevy engines came in 2 totally different castings, a small block 267-400cid & a big block 396-454.
Aftermarket stroker kits & blocks have stretched the small block to 454 cid but that's not a factory engine anymore.

[badazz81z28]

Just how it sounds.
In the chevy land
the BBC and the SBC were basically that. The big block is a Bigger engine block than a Small block

[sikzdrivr]

The poncho motors should be called mb's. Some people call them big blocks but to me there just not the same as far as big goes. I know the poncho motors have tons of potential and are great for making torque, but they just don't have the same appeal. Peoples drop their jaws when you open your hood and they see a real big block (chevy) .

[night rider]

The buick, olds and pont. aint a small block, nor a big block. If you had to lump them in a class I would call it in the middle.

Bigger than a SBC, smaller than a BBC, but with heads close to the size of a SBC

On chevy engines the diff in a big and small block is the real size of block. Not really the cubes, or even the bore

Its how wide the block and heads are. If you look at or look up the sizes of the SBC and BBC's you'll see the BBC heads are much wider than the SBC.

As really nothing at all to do with the bore/stroke cubes. You'll see guys with 430+ cid small blocks (aftermarket) and GM even made tiny cid BBC's years ago, like the 348, and 366 tall deack big blocks

And the SBC 400 and BBC 402 or also called big block 400 by some.

Both the SBC and BBC 400/402 uses the same bore and stroke, the BBC 402 has bigger main and rod journals, bigger valves, etc

[badazz81z28]

Big Block Chevy



Small Block Chevy

[Mwilson]

I never knew that a sbc 400 and bbc 402 are same bore and stroke?

[Brian Callahan]

Big Block Chevy

[BluEyes]

I think the SBC was originally called that because it was designed to be a small compact engine - ie: the block wasn't as big as others at the time. When the BBC came along, it was bigger than the already-named smallblock, so what else you gonna call it?

Do the BOP engines even have big or small blocks? Didn't they only have one block casting, just different strokes and bores between them?

[night rider]

Mwilson...
Yep both big and small block 400/402 are 4.125" x 3.76" (or 3.75") bore and stroke

The small block 400 has 2.65" main journals and 2.10 rod journals, the big block has 2.74" mains and 2.20" rods

BluEyes... Your right BOP just had one casting, no big and small blocks

[camaroBob 454]

Brian, At least I'm amused with your cool pic! Thanks for sharing!