michael l

i have a 75 cutlass with a 350 4 barrel all stocki want to raise my compression a bit thinking of using cometic gaskets along with a small cam with448/472 my question is would i have to makes changes to the rest of my valvetrain

fleming442

Stock valve train is capable of. 474 lift (so, I hear). You should be fine.

joe_padavano

If you currently have the original steel shim head gaskets, anything else will be thicker and lower compression.

Your problem is that your number 8 heads have 80cc chambers.

Fun71

A 1975 350 engine would have #8 heads with large 80cc combustion chambers, so finding a set of earlier heads that have smaller combustion chambers in the 68cc range would help raise the CR, especially if they were milled a bit to compensate for the thicker aftermarket head gaskets. The #8 head engines used pistons with smaller dishes to get the same 8.5:1 CR as the 71-72 engines, so using the smaller chamber heads gives a nice bump in compression.

michael l

i dont think they put steel shim gaskets in 1975 small block

olds 307 and 403

Yes, they did. I pulled apart two 76 350's with the shim head gaskets. I found the #8 heads measured 77 to 78CC compared to the 79cc spec. It still means high 7 to 1 compression with the factory pistons probably .025" below deck at TDC. I used that cam in a factory 76 350, it did Ok, 9.9 in the 1/8 with ignition break up over 4000 rpm. It was in a lighter 88 Cutlass, 3750 pounds with a TH2004R and 3.42 gears. It will do better with a higher stall than the factory 1600 rpm.

michael l

i have a set of #7a heads laying around any better?

Fun71

Yes, the combustion chambers are around 10-12cc smaller than the #8 heads (~68cc vs ~80cc).

olds 307 and 403

The 7A are 10cc smaller but adding the usual .042" Felpro head gaskets will gain about 1/2 a point of compression with shitty quench over #8 with the factory shim head gaskets. The other benefit is the exhaust bowl area vs the #8. There is a lip directly under the #8 exhaust valve the requires a grinder or a bowl hog cutter to remove to flow as much as your 7A heads. Good luck.