Alright! Great discussion going on here


>Just because a turbo is rated at 500 cfm @ 2.0 PR does not
>mean that the turbo flows that amount of air in our engine at
>15 psi boost pressure.

Well, it may not be exactly that much air, but if you think about it, thats what a turbo is doing. Its "forcing" all the air it can for each pound of boost. Think of psi as the "work" to getting the air into the motor. We are forcing more air than the motor, VE, and displacement can normally take on. Thats where the power comes from. When we force more air and fuel into the motor, we get more power.

The engine mass air flow is determined
>by the displacement, the RPM, the volumetric efficiency, and
>the air density (or plenum air pressure and temperature). At a
>given RPM and at the same plenum air pressure and temperature,
>the same amount of air flows regardless of which turbo is
>used.

But we must remember, we are forcing the air/fuel mix into the motor with boost pressure. VE, and displacement has a bit to do with it, but we are squeezing the mix into the engine. A bigger turbo can "squeeze" more air into the motor, because of a larger compressor wheel, that can collect and push more air over a smaller turbo.
>
>Bigger turbos put out cooler air - so you can get more power
>out of them.

Actually, it almost is the opposite. With larger turbos, comes more heat from compression of the air. Think about a air compressor for like air tools. Feel the outlet of the compressor. I'll bet its pretty darn hot. Why? Because its compressing lots of air. Compressing air particles creates heat in the process. Pure physics there. Yes, colder air equals more power, but not that much. A T25 turbo at 10 psi will get blown away from lets say a T3/T4 hybrid turbo at 10 psi. It just flows more air. Take a look at each of those turbo's compressor and turbine wheels, and you will see the big difference in their sizes. A larger turbo flows more air, plain and simple.
>

13.5 @108 MPH-2.2 60ft(stupid FWD!)
S16G @ 18 PSI/FMIC/Running on MegaSquirt II (Now with sequential
fuel injection)
My webpage: http://eclipsed4evr.home.comcast.net
-1998 Mitsubishi Eclipse RS-T- "Toy"
-1992 Plymouth Laser Turbo AWD(SOLD)
-2000 Honda CR-V(daily)