Originally Posted by ProjectMayhem

They may not realize you were using a compounding boost setup. let me explain this better. in a typical twin turbo setup you have both turbo's feeding into the intake manifold. Your simply adding boost from both turbos together. 14 psi + 14psi = 28psi.

On a compounded boost setup like the one you are building the turbo will compress the air to a desired PSI then travel to the inlet of the supercharger. The supercharger then takes what ever pressure is at the inlet and compress even further(at a rate of multiplication not addition) Think of it this way atmosphere already is at pressure naturaly and varies depending on weather and alititude.

Atmosphere at sea level is 14.7 PSI
Turbo set at 14 PSI
Supercharger w stock pulley is 14psi

First lets figure at what rate of multiplication the supercharger is producing at peak boost.

14psi from the supercharger plus atmosphere of 14.7 = 28.7 psi
So we divide 28.7 by 14psi and we get 2.05

So now we know the supercharger will compress the air coming in at a rate of 2.05 times the inlet pressure

14 psi from the turbo plus atmospere of 14.7 = 28.7 PSI

So we take 28.7 PSI and multiply it by 2.05 to figure out what our total boost after the compound setup.

Which 28.7PSI X 2.05 = 58.8 PSI(boost+atmoshpere)

Dont forget to take atmosphere out of your total boost. So we minus that 58.8 - 14.7 = 44.1 psi at the manifold

This same calulation with a 5lb wastegate on the turbo would give you a total boost of 25.7 psi at the manifold.

Hopefully that explains how you calculate total boost on compound setups a little better.