Blue Eyes
>The compression ratio is the numerical comparison of the
>volume contained by the cylinder plus the cylinder head when
>the piston is all the way down at the bottom of its stroke
>(this position is called "bottom dead center" on the
>crankshaft rotation) compared to that same volume at the top
>of its stroke, or "top dead center."

 I missed the first part of this, but I'll jump in anyway.

One thing often not considered on four stroke engines, the above it the
way to figure uncorrected compression ratios. The proper 'corrected'
compression ratio would take into consideration how late the valve closes
as the piston is rising on compression. The longer duration the cam, the
lower the corrected compression ratio.
 Two-strokes will generally give corrected ones, since they are taken
from when the exhaust port closes.

 The best way to test for compression loss- a leak down test. You can
then tell where and how much any loss is. Under 10% is good.

mark