Yeah, I'm really at a loss for how they are coming up with 500ci & 10 / 10 1/2 - 1 compression. . .the only stroke that would make sense would be 4.375 & with the .051 head gasket the cr would be 11.8 with a 78cc head. With an 85cc head the cr would be 11.3 which still seems to high. Maybe the timing is very retarded for pump gas ? I'm going to check timing and pull the oil pan soon. Hopefully I can find some marking on the crank that will help out. . .talk about detective work. . .& at the end of the day I don't see it making the claimed HP with such a small cam & 750dp. . Plus I have to change a valve seal