I have noticed that this question comes up from time to time, and had the opportunity to take a few illustrative photos, so I figured I might as well post them.

When identifying Olds engines, it can be hard to tell the diference between a big block and a small block, because most of the bolt-on parts, including heads, can be interchanged (whether successfully or not), and therefore look very similar to one another. Also, they may have in fact been swapped by some prior owner, leading to confusion.

The only major external part that CANNOT be bolted from one to the other is the intake manifold, so that is a guaranteed way for a newcomer to be able to tell the block type, short of memorizing casting numbers.

Also, by coincidence, these photos illustrate the difference between a divorced choke manifold (the red big block manifold shown) and a hot-air choke manifold (the gold small block manifold shown).


Gold 1970 Small Block Manifold with Hot-Air Choke on Left,
Red 1968 Big Block Manifold with Divorced Choke on Right



- Eric