Hello. I was going to put them Vortec heads on my '92 chev 350 1/2 ton. i know that the bottom end of the engine is all stock and stock has dished pistons but i dont know how much they are dished. But the stock compression of the engine is 8.5:1. Now i was going to put a gm comp head gasket that is .028" compressed. What would my compression ratio be with the new heads, this gasket, and stock gm dished pistons?

 

Your stock heads have the same chamber volume as the vortec heads (64cc). If you use the stock type gasket, compression will remain the same. I believe the stock gasket is a steel shim (.015-.019 thick). Using a thicker gasket will lower your compression ratio.

 

Hello. Are you sure that they are 64 cc already? I thought that they were 72 or 76 cc chambers. When we took off my friends heads off of his '91 GMC 350 sierra ST to put on Edelbrock performer heads... the chambers were much bigger than 64cc. Im sure of this. Maybe in '92 they were different? I dont know.

 

Perhaps I'm mistaken. Anyhow, if you go from 76 to 64cc heads and keep everything else the same, you will gain 1 point of compression. 9.5:1 in your case *may* be too much with the stock cam; resulting in detonation.

Check out: http://prestage.com/carmath/

 

Just use higher octane and a lower thermostat to be safe from detonation.

 

You should be ok with 92-93 octane and 9.5CR.