When elko69 was making his inquiry about determining his Dynamic CR after the motor was built I ran across this article.

http://mgaguru.com/mgtech/power/pp105.htm

Cylinder pressures are directly related to CR and atmospheric pressure.
CR is also a function of atmospheric pressure as a denominator.

So, the lower the atmospheric pressure, the higher the resulting CR.
Although the theory is sound, I do question the fact that in this example, 190psi cylinder pressure yields only 6.5:1 CR

The article states:

"It all goes back to PV=nRT."

(At sea level atmospheric pressure is 14.7 PSI)

When the gauge pressure reading is 190psi, the absolute pressure is 204.7psi.
P1=204.7
P2=14.7
V2/V1 = effective compression ratio

V2/V1 = (204.7/14.7)^0.71 = 6.5/1
SURPRISE !!!

The "1" is the total volume above the piston at top of stroke.
The "6.5" is the effective piston displacement plus the final top volume
Effective displacement is then only 5.5 parts of that 6.5 total.