gritten

I recently acquired a 68 442. Block is original, but someone swapped the C heads for G heads during a rebuild. Anyone else in this forum have experience with this combo? If so, I'd very much like to hear your thoughts/comments. Is it worth getting C heads if the car is to be primarily a cruiser? Thanks.

Fun71

The only significant difference between the heads is maybe the valve sizes. I say maybe as C and G both came with small and large valve versions. I wouldn’t lose any sleep over it.

gritten

Thanks for the feedback. Combustion chambers are larger on G heads (80cc) so I've clearly got lower compression than stock, but presume engine was rebuilt with G heads to run better on lower octane fuel. Car seems to run well, but won't win many drag races. 😉

cutlassefi

All big block heads (except D’s and J’s) will avg 80-82cc’s anyway.

gritten

I see that now....thanks. Clearly I'm an Olds noob. Merry Christmas to all!

Fun71

Olds changed the compression ratio by using different size piston dishes. The heads had the same size combustion chambers, aside from what Mark mentioned above.

joe_padavano

Combustion chambers on every BBO head casting except the "D" heads run about 80cc. There will be zero difference in CR (except for the half point drop due to replacing the OEM steel shim head gaskets with thicker aftermarket composite gaskets).

Sugar Bear

What is the CC on D heads? What were they used on?

joe_padavano

D heads are 1968-69 W30 and H/O. As-cast were typically around 72 cc. NHRA blueprint spec is 69.7 cc (vs 77 cc for all other BBO heads).