According to Cspeed's calculator, a -9.3 cc dome piston in a GSR will yeild 8.74:1 compression ratio. According to the manufacturer of said piston JE, it is a 9.0:1 piston for the GSR. Someone must be wrong here. This was done for a .020 oversized piston, but it is wrong for the stock bore 81mm piston as well.

 

Anyone have an idea? I have these pistons in my kitchen, but if they are actually lower compression than advertised, I think I will want to raise it.

 

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I just did a calculation with a .020(3.209) overbore, same size head gasket(3.209), .042 thick, with a .003 deck clearance, stock stroke, stock cc head, and came out with a static compression ratio of 9.004:1. I'm sure it will be a little different than that. But that's pretty close. What size head gasket does JE say to use with those pistons?

 

So CSpeed calculator=crap I guess. I won't use that thing again.

 

I was told a few months back the C-Speed calculator is a little off.