<<<<Scott

Last time I checked, cubic inch DISPLACEMENT includes only the swept
volume as George says. Pop up pistons, etc. only change the FIXED
volume above the piston. Displacement happens only when the piston
moves up in the cylinder, displacing cubes as it goes. It is calculated
simply by multiplying the cylinder bore by the stroke.

Check me if I am wrong.

Doug>>>>

Exactly correct.  Most of our engines have a stroke of about 4.25 inches, so
if the combustion chamber were a perfect cylinder an 8.5 compression engine
would have a clearance of 0.567 and a 9:1 would have 0.531.  Therefore, you
have to add 0.036 to the height of the piston to change from 8.5 to 9:1,
assuming you added it uniformly across the surface.  No change in
displacement at all.

Gary Casey