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WOW, you freeking LOST me!No, it sucks and goes bang.
At the RPMs normally used for a compression readings , an engine with a 10 to 1 CR and a short duration low lift cam will normally show readings higher than said engine with a high lift long duration cam . The opposite is also true at high RPMs , a camshaft with bumpier specs will produce higher readings , or greater BMEP . It's what we used to call "coming on the cam" . The static pressure at BDC in an IC engine is almost never atmospheric pressure, it is normally higher , although with extreme camshaft specs it can actually be lower . A static CR of 10 to 1 in a well set up IC engine will normally produce static high pressures in the 170 PSI range , not the 147 predicted by multiplying static atmospheric pressure by 10 . And no we aren't breaking the laws of physics , only applying them in the conditions existing in the IC engine . Dusty
Is it true, or at least roughly correct, that expected cylinder pressure is just the product of the compression ratio times the atmospheric pressure? For example. Assume atmospheric pressure is 14.7 psi. Your engine has a 9:1 compression ratio. Do those facts imply that a perfect condition engine would generate 132 psi on a compression test?Maybe there’s a fudge factor where you deduct 5 to 10%?
Oh stop it now Steve....You’re just being characteristically modest... BTW..It’s freaking....
Does this mean if there low pressure in forecast you can have less CR? Wow, who knew.
Well I guess the ratio won’t change, but the mass of air intake will.
It would be better if there was any money in this knowledge , sadly there isn't . TS
A compression gauge is a diagnostic tool only because absolute readings will vary depending on cranking speed and temperature.Compression numbers are significant only if (1) there’s a big difference between cylinders, or (2) the numbers are really low, like 50psi or something. Is a motor which shows 150psi on one day in better shape than another motor which shows 130psi on a different day? I don’t think you can say that.
That’s interesting Phil. But why is that the case?