Most domestic manufacturers back in the muscle car era made two different blocks. The small block and the big block. Both were generally available with different bores & strokes to generate different engine displacement.
Therefore from Chevrolet you could get a small block with a 265, 283, 302, 307, 327, 350 or 400 cu in displacement, all with the same external block dimensions. In later years they came up with some other oddballs like the 262 and 305 cu in variants.
In the big blocks you could get a 349, 409, 402, 427, 454, 502 and 572 cu in motor, all with the same external block dimensions.
Notice that there's some overlap too. You could have a 400 cu in smallblock (which looks no bigger than a 283) parked next to a 349 big block and you'd swear the 349 was huge compared to the 400. It wasn't uncommon to see a 427 with hydraulic lifters powering a station wagon and then the same motor with a huge cam and solid lifters powering a COPO Camaro. One ran as smooth as an electric motor, the other idled like a funny car.
There are variants within each class like 4-bolt main and 2-bolt main motors. The 4-bolt being more desirable for making big power.
Also, the GM LT & LS motors are not members of either family. While the LT motors are based off the small block, they have little in common with then and most parts are not interchangeable. The LS series motors are a completely new design and are radically different from the old small block & big block. Most production motors today would be considered "small block" due to the package size and cu in displacement.
Can you tell I'm an old GM motorhead?
That about covers it for Chevrolet. Most GM's are similar although there are some odd variations like the 90 degree V8 Buick motors...
Someone else will have to tell you about the Ford crap. :icon_razz
