compression change from smaller combustion chamber?

[rrubel]

I was under the impression that the combustion chambers in my cast iron heads were 64cc. A couple people at Carlisle told me that. Now, looking around the web, I find they appear to be 76cc. However, I've already bought, modified, and assembled heads with 64cc chambers. This should raise compression somewhat, right? Anyone know by how much, all else in the engine being equal? I have no problem running 93 octane instead of the specified 87, but don't want to live at Sunoco for 104...
Thanks.
[RICHR]

 

[Eagle85C4]

not sure...but TPIS has a head gasket a bit thinner that is supposed to jack the comp ratio up a 1/2 to 1 point.....0.29" instead of 0.39 " stock. FYI

 

[6shark9]

Not considering piston "scallop" and gasket thickness you would bring a 9:1 up to about 10.5:1 going from 76cc to 64cc

or in your case 9.5:1 would go to almost 11:1

 

[rrubel]

Thanks for the link. Now I need to find the dish/dome volume number - have everything else, but if I use the TDC vol listed in Cor-vette specs it comes out to a CR of 10.5 on the STOCK motor, which is 1.0 too high. So the published TDC vol doesn't appear to take gasket volume, deck volume, or DDV into account.

Never mind. Remembered my basic algebra and solved for the unknown and determined (if math is correct) that new CR will be 10.9:1. Is this too out of line? Should I get a thicker head gasket? The one I'm installing is slightly thicker than stock to begin with.

[RICHR]

 

[Eagle85C4]

The old trick was to put a dab of modeling clay on the piston then install the head. Turn motor over , then remove head to see what kind of clearance you will have or if there is a problem....

 

[rrubel]

It was less of a clearance issue than of a "how badly will I knock" issue... or will I start blowing gaskets-type of thing. The heads are designed for the stock pistons, so they darned well better not hit... I'll try the clay trick, though, before putting everything together.
[RICHR]