I did the math and came up with higher numbers than that even. Actual displacement of the 1.6 is 1.588L. or 1588cc. 1588 / 23 = 17.26 giving the entire volume of the stock combustion chamber. Using Boyle's Law (P1*V1=P2*V2) and a P1 of 450 psi, given the stock chamber size of 17.26 and the chinese chamber size of 17.26 + 2.5 this is what I come up with: P1*(17.26 + 2.5) = 450*17.26P1 * 19.76 = 7767 P1 = 393Soooo, if a stock combustion chamber pressure was 450 psi, then with the added 2.5 cc of volume in the Chinese head, that pressure would drop to 393 psi. Obviously there is some other issue at work as well. What compression gauge was used? What method? Andrew