Psi vs Cfm Options

[KOU In3]

Ok, I've always been led to believe that CFM was more important a measure than psi and that the larger turbos flow grossly more air at a given psi than their smaller brethren. I understand the basic part that the hot air produced when the turbo is overworked leads to a higher psi reading from the same quantity of actual air.

Here's where I start to get confused though: if we keep the intake charge's temperature constant through effecient intercooling shouldn't these values be the same? Basicly if you pressurize the manifold to 20psi using 120 degree air from a 14b or the same temp and psi from say a mammoth BR580 shouldn't this be using the same cfm of air?

Right when I think it all makes sense I talk myself back into the classic fallacy of 'dude it's 20 psi!'. Is the Someone straighten me out here please.

[ICGerms]

...I understand the basic part that the hot air produced when the turbo is overworked leads to a higher psi reading from the same quantity of actual air...

I think that you're confusing yourself on this...hot air isn't going to produce more psi. An "overworked turbo" will produce more air, albeit hot air. A turbo that is not being overworked (e.g. a larger one) will produce the same amount of air (in cfm) but that air will be at a lower temperature. In other words, the larger turbo is more efficient in producing the larger amount of air. Also, the larger turbo will be better able to produce more cfm at lower psi than the smaller turbo. Say turbo X produces 100cfm @ 15psi and turbo Y produces 200cfm @ 15psi...turbo Y is the bigger turbo. Sure, turbo x could probably produce 200cfm, but it would have to do so at a higher psi...30psi, for example. Since turbo X is most likely out of it's efficiency range, it is producing those 200cfm as hot air now, while turbo Y is able to produce it's efficient (15psi) 200cfm as nice, engine-friendly cool air.