[logician]

Hi,

> Since the test is to determine the "percentage" of air leaking
> from the cylinder, theoretically, it will leak the same percentage
> regardless of engine size, orifice size or pressure.

I think orifice size does make a difference. Consider the following example: if the pressure inside the cylinder under test is 50% of the calibration pressure (pressure applied to other side of orifice), then that means that the total of the "leakage area" around the rings and valves would be equal to the orifice area.

So if you used a second instrument with twice as large an orifice area, then the leakage area needed to get a 50% reading would be twice as large. Thus this second instrument would be much more optimistic if you only considered the % measurement without considering orifice size.

Thus if you want to compare measurements from different instruments, you need to consider their relative orifice sizes. Also, the orifice size really is needed to interpret whether the percentages you measure indicate a healthy or sick engine.

-Juan