Calculating Compression
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Joined: Nov 2005
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From: Greens Fork, Indiana
Calculating Compression
I know I've seen it somewhere, but can't find it now, but how do you calculate compression ratio? I'm assuming you need to know the combustion chamber volume, but I've heard that it varies from the factory stock figures. Does anyone have any good info on this? I've got a stock SERK with 103" engine that I'd like to know the compression ratio in stock configuration and then calculate what it would be with milling the head or thinner head gaskets.
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Joined: Nov 2005
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RE: Calculating Compression
Need to know head volume chamger size, gasket thickness, piston dome top volume,piston deck height,bore,stroke. Then you can calculate with some decent accuracy your static compression ratio. If your off only a few cc's though your figures can be off significantly. If your running your stock heads then you will absolutely need to cc those heads manually, becuase there is a BIG VARIANCE between stock HD heads. I have seen HD bikes with real static CR as low as 8:1 and as high as 9.6:1 from a stock bike with a factory "rating" of 8.9:1.
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