The Project Pad

Static or cranking compression pressure is what each cylinder
experiences when the starter motor is turning the engine or when
the engine is running at idle RPM. Please don’t confuse static
compression with “compression ratio” which has to do with how
much volume remains in the cylinder when the piston is at the top
of its’ stroke. Static compression and compression ratio are related
but the definition of each is different.

Compression pressures that are too high can result in difficult
starting and detonation or “pinging” which in turn can cause
engine damage. These high static compression pressures are a
result of compression ratios set too high, intake cam duration too
short or the intake cam timing set with too much advance.

Low compression pressures translate to poor low RPM torque. Causes for low compression pressures are late intake cam timing,
too much intake duration or a compression ratio set too low.

Modifying an engine by changing pistons, camshafts or compression ratios will have a direct effect on static or cranking compression pressure. If the static compression pressure is too high or too low, the engine will not run as well as it should and in some
cases, the resulting problems can be serious. Static or cranking compression can easily be measured with a COMPRESSION
testing gauge. Cost is usually less than $25.00 and most auto sup-ply stores or well equipped motorcycle shops sell them. To measure static pressure, the procedure is as follows:

With a warm engine, turn off the fuel from the tank, make sure the choke is off and the transmission is in neutral. Remove both
spark plugs and insert the gauge adapter in one spark plug location. Now, holding the throttle wide open, turn on the starter motor
and read the pressure indicated on the gauge. Then repeat the procedure on the other cylinder. The figures on the next page give
some idea as to the significance of different pressure readings. Also some gauges have a rubber tip instead of a screw in adapter.
Either way, reading the static pressure of your engine should be fairly easy. Generally, higher static pressures mean more
torque at lower RPM ranges but the trade off is that above a certain point (around185 PSI) the risk of detonation enters the picture. What happens at higher RPM is less predictable and can’t be easily determined from a static pressure reading. What is important is that the cam timing, duration and compression ratio all be properly matched so that each compliments the others.[/quote]

and this place is a calc to apply the info....

http://www.rbracing-rsr.com/compstaticcalc.html