I have'nt got the time to explain in detail, its actually a very complex issue. I'm trying to get a feel for the average understanding , people have of compression ratios but I think the problem is people dont fully understand it is a dynamic condition that varies vastly with other engine components. So for example I could build two zetec engines both 300bhp, one would det itself to death at 9.0:1 the other wouldnt. Anyone want to guess why?