The 906's were never milled and I never cc'd each cylinder to check consistency. Going by production numbers, I'm assuming the heads are somewhere in the 88-90cc range, so based on the KB piston specs of 1.8cc piston step & stock stroke, compression is 10.5:1 @85cc's, 10.0:1 @90'cc. with a 0.040" gasket compression, or 10.96:1 @85cc to 10.45:1 @90cc with 0.020" compression.

I'm guessing what your driving at is, I should have cc'd the heads and equalized them, then measured the piston step to calculate exact compression ratio & quench.