OK so we'll shoot for the middle and say 525 hp.
Wa = HP x A/F x BSFC / 60 620 x 11.7 x .85/60 = 102.76
Wa = Airflow actual (lb/min) 102
HP = Target flywheel HP 620
A/F = Air Fuel Ratio 11.7
BSFC = convert hours to minutes divide by 60
MAPreq = Wa x R x (460 + Tm) 102 x 639.6 x 590 = 49.98 Psi(A)
VE x N/2 x VD .85 x 3000 x 302
¬∑ MAPreq = Manifold Absolute Pressure (psia) required to meet the horsepower target
¬∑ Wa = Airflowactual(lb/min)
¬∑ R = Gas Constant = 639.6
¬∑ Tm = Intake Manifold Temperature (degrees F) (130 typical intercooled temp)
¬∑ VE = Volumetric Efficiency
¬∑ N = Engine speed (RPM)
¬∑ Vd = engine displacement
49.98 (Absolute press.) -14.7 (atmospheric press.) = 35.28 PsiG (PsiG = Gauge pressure)
I will assume that there is a 2 psi inefficiency loss. So to determine the Compressor Discharge Pressure (P2c), 2 psi will be added to the manifold pressure calculated above.
P2c = MAP + ΔPloss 49.98 + 2 = 51.98
¬∑ P2c = Compressor Discharge Pressure (psia)
¬∑ MAP = Manifold Absolute Pressure (psia)
¬∑ ΔPloss = Pressure Loss Between the Compressor and the Manifold (psi)
P1c = Pamb - ΔPloss 13.7 = 14.7 - 1
¬∑ P1c = Compressor Inlet Pressure (psia)
¬∑ Pamb = Ambient Air pressure (psia)
¬∑ ΔPloss = Pressure Loss due to Air Filter/Piping (psi)
With this, we can calculate Pressure Ratio using the equation.
P2c / P1c = Pressure ratio 51.98/13.7 = 3.8
With these figures calculated you can plot it on a compressor map.
So look at your compressor maps and plot the following points:
Pressure ratio = 3.8 - usually X-axis
Compressor Discharge Pressure = 51.98 - usually y-axis
When you find a turbo with these points on an efficieny island, you've hit the efficiency jackpot.