On this subject of compression testing...A question for anyone with thermo-dynamics expertise...Atmospheric pressure is about 14.6psi. So if I have an engine with 10:1 compression, in theory, the maximum cylinder pressure with no losses through valves etc would be 14.6 x 10=146psi. In practice, at BDC, the inlet valve is still open and the pressure in the cylinder is probably below atmospheric, so on the upward compression stroke, by the time the inlet valve closes there is even less swept volume to compress, which would result in something even lower than 146psi. So why do we achieve readings of 170psi upwards?
Is it something to do with heating of the trapped air under compression?
Simple explanations welcomed please.
