In the interest of learning something new and in not hijacking another thread, I want to post my questions here in the hope that some of you with more engineering knowledge than I have can sort me out. The thread that I am trying not to derail is this one -
www.kzrider.com/forum/2-engine/609912-19...in-blown-head-gasket
The discussion concerning wet versus dry compression tests has been a fairly common one that leaves me with more questions than answers. To wit-
Typically, when we discuss compression ratios, we are talking about the calculated (rarely actually measured) ratio between combustion chamber volume(with the piston at TDC) and cylinder volume plus combustion chamber volume. Expressed as a ratio, the combustion chamber volume is 1 and the other side of the expression is the total volume of the cylinder and combustion chamber when the piston is at BDC. As 650Ed has so clearly demonstrated, removing volume from the whole has a linear relationship to the calculated ratio.
However, what most discussions here are about is measuring combustion chamber pressure. This, in my mind, is a wholly different kettle of fish.Does removing volume from the combustion chamber have a linear effect on measured pressure? Is there any reliable relationship between measured volume and measured pressure?
Put another way, If we measure 120psi in a cylinder, we would have a pressure ratio of 0:120. To convert this to a more useful expression, we need to include ambient pressure, which our gauges show as 0. If we add 14.7psi (typical sea-level pressure) to each side, then divide by that same amount, we get 9.16:1. Does that mean that every cylinder, no matter its volume or design, will have the same volume ratio and pressure ratio? I am pretty sure that this is not the case, as changing the cam profile will change the pressure readings. Is there a dependable relationship between the two?
I am so befuddled.