A specific compression number isn't important, as 3 different gauges used to check the same cylinder will probably give you 3 different pressure readings. What is important is the percentage difference between cylinders, which should be within 10%- - - - a sub-5% variation is better. Sometimes something as simple as valve adjustment or a temporary buildup of carbon in the combustion chambers can make a measureable difference. It takes a couple of tablespoons of carbon to change compression pressure noticeably. The camshaft profile will also make a difference in measured compression, no matter what the theoretical ratio is.
Jerry
