Originally Posted by curtis73
Purists will say that there is no such thing as small and big block olds, and I'm one of them. They differ only in deck height, but heads, exhaust manifolds, and many internal guts are the same. The difference between small block and big block olds is no different than a BBC with a standard deck height and a BBC with a tall deck height, so they are the same engine family.
But, if there were big and small block olds, yours would be small. When buying parts for it, they will be advertised as small block olds parts.
Offenhauser used to make a 3-2 intake for BBO, not sure about SBO. A good example of a 3-2 BBO intake can go for as much as $1500, so be prepared for a shock. I saw one last year at Spring Carlisle that was beat, scratched, greasy, a couple bolt holes stripped, and they were asking $775.
You are of course correct ( I use the example of the B and RB series MOPAR motors), but since there is no legal definition of big and small block, conventional terminology calls the short deck motors small blocks and the tall deck motors big blocks.
While the exhaust port flanges are the same, the exhaust manifolds and headers are not. You can physically bolt a big block header/manifold to a small block (and vice versa) but you won't necessarily be able to actually install it in the chassis. Due to the deck height differences, the headers and exh manifolds for the BBO are taller. Many have tried to install the individual runner W/Z manifolds on the SBO and all have failed. The manifolds hit the motor mounts, starter, and oil filter.
The intake manifold on a BBO is about 1 1/2" wider than on an SBO. The ports are also differently sized. I have never seen an aftermarket 3x2 intake for any 64-up Olds motor, only the factory intake used on the 1966 442s. Yes, those are currently worth their weight in gold. There are lots of aftermarket multi-carb intakes for the 49-64 Olds motors. These do not interchange. Offy does make 2x4 intakes for the SBO. They pop up on Ebay frequently. There are also a few factory experimental intakes floating around. In the late 1960s Olds build a number of experimental intakes (Weber and cross ram, for example) in support of the CroSal Can-Am racing team.
Internally, the architecture is the same, but there are some differences. The BBO uses larger main and rod bearings, so the cranks do not interchange (thought the Olds diesel blocks do use the BBO bearing sizes). All the reciprocating parts are naturally different, as are the pushrods. Cam, lifters, timing set, distributor, oil pump are all the same. Oil pans will also interchange, but the BBO pans have additional bulges - I'm guessing this is for enhanced oil return past the larger counterweights on the crank.