blykins,
One thing that must be considered here.
Compression rings do not seal because of static tension to the wall.
They seal due to combustion pressure.
The combustion pressure pushes the rings outward toward the cylinder wall.
Gap will certainly effect the pressures imposed on the backside of the rings.
However, a simple equation relative to gap will give you bad numbers.
What you need to measure is BMEP relative to end gaps.
And extrapolate the numbers RE: End gaps.
Calculus will not get you there by itself.
One must not forget the thermal effects as well.
Now that I have cleared that up!!!!
