Since I'm unsure exactly what I've got in my two rebuilt heads (I posted previously about this) and as someone had asked what the effect of a flycut of .03" would be on the compression ratio, I decided to build my own spreadsheet to calculate compression ratios, and see what the effect of an "extra" or "missing" shim between the head and cylinder would do to the compression ratio. The thickness of the head shim shipped with the gasket kit seems to be right at .031" or so, just about the same as the above-mentioned flycut. (My problem is that I have reuilt AMC heads and VW heads and I'm not sure if I should be using the shim in the AMC heads, or not.) The figures below labeled (calc) are calculated based on published figures for a stock 2.0L Vanagon engine, or "typical" figures mentioned by posters. The (guess) figures come from other posts where people have either reported the measurements they've taken or read about. Total Compressed Volume Volume Swept area (calc) 492.726 N/A Piston dish (guess) 17.000 17.000 Deck height (.04")(calc) 7.079 7.079 Combustion chamber (guess) 48.000 48.000 Shim (calc) 5.482 5.482 --------- --------- Ratio 570.726 77.561 7.35 ======= ======= Remove shim 564.805 72.079 7.84 ======= ======= Add extra shim 575.769 83.043 6.93 ======= ======= Clearly the addition or removal of a shim (or flycut) has a big effect on the compression ratio. Looks like I'm going to have to cc the heads or risk some problems. Sigh. --------------------------------------------------------------------- Tom Young young@sherlock.SIMS.Berkeley.EDU Lafayette, CA 94549 '81 Vanagon --------------------------------------------------------------------- |
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