I want to make atleast 9.5 compression and I think these two will make around 9, should I have the heads milled or get another type of piston???

GM P/N 10159437 - "This piston makes 10:1.1 compression when used with a 58cc cylinder head .051" head gasket"

and AFR 195 68cc with heatriser heads

can anyone let me know what the compression would be, is there a formula to it??

any help is most appreciated.

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1989 Trans Am GTA, L98 5.7L TPI, TH700-R4, T-Tops, dual cats, 9-bolt rear, 3.27,
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Honda engines ROCK, I have one on my lawn mower but I still have to push it.

 

It depends on what your deck height is too. You can get a thinner head gasket to raise it too. You basically add the area in the deck height, piston reliefs, and head gasket thickness. If you can get those specs, we can figure it out. I use AFR 195, with a flat top, 355" piston, .012-.016 deck height, and a .038" gasket. I figured it to about 9.6-9.7 to one. I got the formula from John Lingenfelters book.

 

If you want to raise compression you could also have the heads milled slightly.

 

http://www.prestage.com/carmath/

 

Just changing from 58 to 68 cc heads will lower the compression to 9.1 from 10.1
You'd have to cut the chamber to 64 to get to 9.5. Probably a good idea would be to run a thinner gasket (.051 is really thick) like .039, which will put compression at 9.3 with the 68cc heads. There are some issues like how far the piston is down at TDC, but I just kept it constant at 0 to compute the compression ratio. If its stock, it will probably be about .020 or thereabouts, so you will want a thinner gasket to maintain the quench area.