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Compression ratio is not too hard to figure out with pistons that have a flat ridge around the edge like JE's.
The basic idea is to figure out the volume of the cylinder with the piston at the bottom of it's stroke (Vbdc) and divide it by the volume of the cylinder at the top (Vtdc) of it's stroke.
CR = Vbdc / Vtdc
Vtdc = Vhead - Vpiston_dome + (A * deckheight)
Vbdc = Vhead - Vpiston_dome + (A * deckheight) + (A * stroke)
A = bore area = PI * r^2 = PI * (.5 * bore dia) * (.5 * bore dia)
Let me know if you want more detail (like how to measure piston dome volume for example).
-Chris
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