My car is pretty predictable. It's be right about 20hp per psi (turbo) all the way from 10psi up to 23psi. Thats based on ET/MPH, not any dyno fabricated numbers.

You have to remember most ways to create boost (good size turbo or supercharger) is REALLY inefficient at low boost. So the efficiency actually gets better the more boost you throw at it.

That's why it doesn't fall of like you'd think after 5psi as long as it's got a good sized unit to work with.

Compressor map at 16psi

http://www.turbos.bwauto.com/aftermarket...rsin=92044&

Compressor map at 5psi

http://www.turbos.bwauto.com/aftermarket...rsin=92044&


Basically ~18hp per PSI with these numbers...