> Hmmm, seems I can't multiply. 75% of 29.92 is more like 22.5 but that > does not agree with your numbers. Maybe it is not a linear relationship > like I am doing it. Someone knowing more than me please help! > Obviously we are looking for numbers for non turbo engines here.
Interesting, I had never actually thought too much about the relationship between power and manifold pressure. What is clear is that max power is unlikely to be achieved at 29.92, that would assume a perfect induction system that provided full flow ie the carburretor and filter provided no air resistance whatsoever. A carb would not work if that was the case, as you need the venturi to suck fuel. I suppose it would be possible with fuel injection - one reason why fuel injection delivers higher power. I would imagine that the power depends not only on the mass air flow, but also on manifold design, a bad manifold may tend to provide a poor fuel air mix to one cylinder and a perfect mix to others, this relationship may vary with throttle setting so a straight line relationship is unlikely. I guess every engine installation has a unique pressure/pwr graph. I have never seen one, I suspect that like much of aircraft design it is an empirical process, the manufacturer does his tests, fiddles, retests and then issues a handbook with some quite broad statement that 75% power = X inches of pressure. Pete
