Thats fancy talk for how much boost? So here is my question I have a new boss302 crate that is 9:1. I have a Hellion turbo kit that I was running on my stock block set up before this motor at 7#. I have been reading about effective compression ratios. And conflicting advice about them. Some say that the total compression ratio should not exceed the 12.4 mark. While others say a good tuner can make higher work safely on pump gas. I have seen plenty of 9:1 cars with 12# or so on them. But for how long? One important thing on my motor is I have switched to an f303. Worked well on my last combo so I ran it on this one also. But that cam has no overlap.So there is no boost bleed off. What is concidered safe compression ratio with boost? Used the calculator and basically with 7# on 9:1 at 2000 ft my ratio would be 13.5:1 ish.