With the 70cc head , pistons down .100 @ TDC and with no valve reliefs with a standard .039 Felpro head gasket, I get 8.874:1 which is really about all you want with a street engine with iron heads with no quench.
Dang, that's lower than I was expecting, considering 20cc less on the combustion chambers... stock wit the 90cc chambers was a hair under 8:1. I'm also not far above sea level, maybe 100ft above, and when I go to new Orleans to run I'll be about 40ft below sea level lol. Also it's aluminum heads. What I meant by guys using 915 heads I was using as a comparison. Which now I've heard and read on forums just by going from the open chamber stock heads to a closed chamber 915 or 516 and a little milling would bring 9:1 or more, and I know my chambers are smaller than that, then again what some claim by saying something like that don't mean it's true... and on roadkill with their crop duster project they put the eddy rpms onto a low compression 440 and they have 84cc or 88cc chambers and they said the compression was like 8.4:1 I think.