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Deck = 0.025" X 3.875"
Piston dome = Flattop w/4 valve relief = -12cc(?)
 

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Discussion Starter #3
I plugged this into a compression calculator using a .020 headgasket with a 53cc head and it only came out to 9.32. Does this sound right? I also plugged in the stock 75 cc head and only came out with 7.4.
 

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Sixty-nine & '70 had 9:1 comp. ratio. Seventy-one and later had 8.5:1 ratio.
 

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Discussion Starter #5
So then It should have 8.5:1. So If I use my 53cc heads and a .039 headgasket. It should be some where around 10.2:1. IS this safe to use with 93 octane??
 

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So then It should have 8.5:1. So If I use my 53cc heads and a .039 headgasket. It should be some where around 10.2:1. IS this safe to use with 93 octane??
But you said with a .020 gasket and the 53cc heads you would have 9.32. I think with the .039 you'd be dropping closer to the stock 8.5, or did I miss something?
 

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I've never seen a 307 with anything other than flat top pistons (approx 5cc for valve reliefs). Compression ration changes where generally with cylinder head volumes.
For an approximation they generally come out around .025 in the hole (stock), although this number can vary quite a bit.
 

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Discussion Starter #10
yeah they are 53cc.there tthe "601" 305 heads. I havnt taken the stock heads off so I wasnt sure if hey were flat top or what. I wanna try to use the a .039 vs a .020 gasket to make sure the comprssion doesnt go way to high
 

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Discussion Starter #11
I plugged it into the formula and came up with 9.8:1 with a .039 gasket and 10.4:1 with a .020. I think the 10.4:1 will be to much for 93 octane with the crane 274h06 cam I have is this true?
 

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Discussion Starter #13
I think Ill just use the .039 gasket ang play it safe with the 9.9 since this is a street driven car. With the 93 octane it should be fine.
 

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Just be aware that by bumping up the gasket thickness, you're increasing your total quench height. At some point, the quench height is so large that you lose a lot of mixture turbulence, burn rate slows down, and you become more knock sensitive despite the lower compression ratio. End result is that you would have been better off with a higher compression ratio and tighter quench height.

Please note that I don't know which tradeoff is better in your case (~0.064" quench height with 9.9 CR versus ~0.045" quench height with 10.4 CR) -- just thought it's something you should be aware of. 0.064" quench height is a little large, but there may be no issues...
 
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