3 Deuce 64

I have a friend who just aquired an olds I know nothing about them Ford and Pontiac guy here

Now in pontiacs there are no small block big block heads from a 326 will fit a 455

My question is my friend has a 68 /69 cutlass 350 will 425 heads fit on the 350 block there are some water passages that don't seem to match the gasket . Don

joe_padavano

I'm not a Pontiac guy, but I thought all Pontiac blocks (prior to the 301) were essentially the same, meaning those heads should bolt up.

Anyway, back to Olds. The primary difference between the big block and small block Olds blocks is the deck height (plus main and rod bearing sizes). The block architecture (bore spacing, bolt patterns, etc) is the same, including the head bolt locations. Big block heads bolt directly to a small block. The head gasket holes are deliberately different from the cast holes in the head because the holes in the head are sized to allow removal of the sand used in casting.

Whether putting big block heads on a small block is a good idea is a different question. First, since the big block ports are larger, few intake manifolds seal properly. The Performer RPM is one and it has sufficient meat to allow it to be ported to match. Failure to do this pretty much negates any flow improvement you get from the head swap. Second, small block heads prior to 1973 had 64-67 cc chambers. Big block heads have 80 cc chambers, so unless you plan to change pistons you'll have a dramatic drop in compression ratio. Finally, you can easily install big block valves in the existing small block heads (that's what the factory did with the W-31 motor), eliminating the above-noted problems.

3 Deuce 64

Joe thanks for the information on the heads .

on the pontiac what I said is yes all heads 65 up an all the blocks ofcourse except the 301 only thing that interchanges on those is the valve covers I think but on the regular Pontiac bores 326 350 389 400 421 428 455 you can mix and match now you can change 64 heads and intakes and put the on later blocks if you change the whole upper half and vise versa later heads on a 64 block .

on the olds the heads and intake were missing but he had the 425 motor . i told him to rebuild that will the 350 trans bolt up to it ? Don

joe_padavano

Yes. All Olds motors have the same BOP bellhousing bolt pattern and the same motor mount bolt holes. Use the motor mounts that go with the car, not the engine (ie, if the car originally had a 350, use the 350 motor mounts on the 425). You'll need the correct exhaust manifolds or headers for a big block in the car you're putting it in (in other words, if the 425 is replacing a 350 in a 70 Cutlass, for example, use the 70 350 - not 455 - motor mounts and the 70 455 headers or exhaust manifolds). One final difference is the flexplate/flywheel. Olds changed the crank flange bolt pattern in 68 so you'll need to use the flywheel for the 425.