Originally Posted By: JHZR2
Was next to an old chevy C/50 (I think from the early-mid 1970s) today, and it had a 366 badge on it. Got into reading up on the 366, as it is an engine I hadnt heard of.
But my one question is this - what designates a big block v8 from a small block? For example, GM made a 348 big block v8 that apparently sold, even in cars, alongside the small block 350. What's the difference?
Could I make a 6, 7 or 8L V8 that is not a big block? For example, the old 366 was a big block. Is the 6.0L vortec truck engine a big block? What about the upsize V8 engines used in the vette Z06?
Similarly, GM made some giant V6 engines for medium duty trucks back in the 60s. Are they considered big block, small block, or because they are V6, do they get neither designation?
Thanks!
There's really no consistent differentiator. Back when the term "big block" and "small block" came into use, each of the manufacturers typically had a distincly different block casting for the larger engines than the smaller ones. Mopar had the "LA" series smallblocks (273, 318, 340, 360), the "B" series low-block bigblocks (350, 361, 383) and the "RB" series raised-block bigblocks (413, 426, 440, and an early 2-year only 383). The raised blocks accomodated longer strokes. The Chevy side had the venerable smallblock, and then both the "W head" (348/409) and "Rat" (396, 427, 454) big blocks. Ford had the "Windsor" smallblocks (289, 302, 351, etc.) and then several big-block families including the "FE" aka "Y-block" engines (390,427, 428, etc) and the later "Lima" 370/429/460.Then there were the "Cleveland" engines which related mainly to head design, but the "modified" Cleveland also included a raised deck compared to a Windsor IIRC. Cadillac never really had anything you could call a "small" block until the 80s. Olds had what were called "big" and "small" blocks, but they really only differed in deck height like the "B" vs "RB" Mopars did and both those were considered big blocks because of the bore size.
When you get right down to it, its arbitrary. In GENERAL, though, I'd say that for the most part anything where the block is long enough to support a cylinder bore of over 4" is a big-block, anything with a bore under 4" is a smallblock. But you can immediately find exceptions like the Mopar 340 (bore 4.04") which is still a smallblock because its based on the LA block that started out at 273 CID. Similarly there are big-bore smallblock Chevies like the 400 that are still classed as smallblocks because the block heads and casting derive from the the smallblock, not the "Rat."
Tracing the roots and lineage of today's engines back, you can make the claim (and support it) that big bores notwithstanding, none of the Big 3 still make a big-block at all. The GM LS clearly derives from the SBC, Mopar's 4.7 isn't related back to anything but has nearly the same bore center spacing and exactly the same conrod length as the LAs and is physically small. Same for the 5.7 and "392" Hemis. And the Ford modulars are also physically small and light compared to the old Lima engines.
Now all that's the factual stuff... but I have to say that there's just some intangible difference, too. Since all factory development on big-blocks stopped in the 70s and 80s, even the most refined of them are a bit rough around the edges. They're loud, they're violent, they have more torque than a small planet spinning on its axis, they're thirsty, and they pollute. But boy are they FUN!
