Compression Question

Night Hog · #1 06-23-2008, 02:26 PM

I am looking into upgrading to a 95" big bore kit with andrews 37G cams. My question is, I have read alot about the 37G's running real good about 9.7:1 - 9.8:1 compression ratios, all the kits that I have found have pistons with 9.1, 9.3, 10.1 and 10.5 compression ratios, none with 7.8:1.&nbsp\\;I thought installing say a 10.5:1 piston will give you 10.5:1 comnpression ratio, but after reading dozens of posts I guess it does not. How do you get a 9.7 or 9.8:1 ratio, do you go with certain gaskets, rings, etc. This might be a stupid question but I have never really thought about this before until now. Thanks for your help.

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Colonel Sanders · #2 06-23-2008, 05:05 PM

It's not a stupid question....I think this is something most folks don't have a firm grasp on.&nbsp\\; You can set your CR by a combination of your piston (flat, dish, or dome), your head chamber volume (the "cc" of the head), and your head gasket.

For example, for a 95" you will have 9.8:1 if you use a true flat top piston, a .030 gasket, and a 81.8cc head.&nbsp\\; You could do the same with a 5cc dome piston and 86.8cc heads, for example.&nbsp\\; Any competent head shop can deck the heads to set the desired chamber volume.