Re: Compression ratio converted to PSI

Posted by Jerry/MT on September 06, 2006 at 12:15:54 from (67.72.98.45):

In Reply to: Compression ratio converted to PSI posted by Brad in WI on September 06, 2006 at 02:14:17:

Compression ratio is actually the ratio of the volume of the cylinder at BDC divided by the volume of the cylinder at TDC. I can give you an equation for the ideal compression pressue but it will calculate to high for several reasons. The main reason is that the equation is for a constant mass in the cylinder. In reality you don't have that as the valves don't closed til part way through the compression stroke, so the mass isn't constant. There is also some leakage past the piston and then the fuel get's injected causing some evaporation and a change in the gas properties and the mass. Having said that pcomp = 14.7 x (V1/V2)^1.4 ~ psia, where V1/V2 is the compression ratio. So if the compression ratio is 16, and you're at std day conditions and your air cleaner has zero pressure loss and the fuel is stop cocked, pcomp(ideal) = 14.7 x (16)^1.4 = 14.7 X 48.5 = 712.95 psia.

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