rudypoochris Posted August 8, 2008 Share Posted August 8, 2008 This is a more general question. When doing a compression test, how is it possible to achieve 240psi or so with only 11.5:1 compression? Is this due to discrepancies in gauges? I would think 14.7*11.5 = 170psi would be the max compression the engine could generate, but I have heard of numbers closer to the 220-240lb range. Why is this? Thanks! Quote Link to comment Share on other sites More sharing options...
Nigel Posted August 8, 2008 Share Posted August 8, 2008 Compression ratio is a function of cylinder volume, not cylinder pressure. Pressure is affected by cam timing and the temperature of the gas, which goes up as it's compressed. Pressure at TDC is typically 15 to 20 times that at BDC. Nigel '73 240ZT Quote Link to comment Share on other sites More sharing options...
rudypoochris Posted August 8, 2008 Author Share Posted August 8, 2008 Ah, so the pressure is more typically due to the increased temperature of the air charge? That seems to make sense, thanks! Quote Link to comment Share on other sites More sharing options...
grumpyvette Posted August 8, 2008 Share Posted August 8, 2008 http://victorylibrary.com/mopar/cam-tech-c.htm http://victorylibrary.com/mopar/otto-c.htm you might want to read this Quote Link to comment Share on other sites More sharing options...
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