Compression

The more improtant figure to "aim for" is the dynamic compression ratio. If you go to KB_piston.com, they have a calculator you can play with. That takes into account the rod to stroke ratio, and the closing point of the intake valve of a particular cam grind in relation to the position of the piston in it's cycle. ou can run as high as 9.5:1 dynamic and run fine on todays 93 octane 10% ethanol (around here) fuels. Static compression leaves a lot "on the table" in terms of power if you strickly build by it alone. A modern chamber design, a good pistons design, and aluminum head material, witht eh right cam choice, and good quench will let a static ratio of 11.5
:1 run on pump fuel. I've read of some as high as 13:1 in a perfect design (import 4 valve "hemi" heads). But these egines develop a dynamic ratio of 9.5:1. That's the pressure the fuel "feels" and what makes it want to ignite from a hot spot or poor mixing in the chamber. The 416 I built 2 years ago runs on pump 89 octane, and is static ratio of 10.85:1. The 440 in my buddy's car is a true 10.8:1 with closed chamber iron heads and flat tops, and also runs on pump 93. Dynamic compression on the 416 is 9.2:1, on the 440 is 9.5:1.