Turbocharger Compressor Sizing & Pressure Ratio Calculator
Calculate engine mass airflow (lbs/min & CFM) and compressor pressure ratio (Pr) to plot operating points directly onto turbocharger compressor maps based on target horsepower, boost PSI, displacement, and volumetric efficiency.
Engine Parameters & Boost Target
Manifold boost pressure (1.24 bar)
122 CID
Core pressure drop (typically 1.5–2.5 PSI)
Compressor Map Operating Coordinate
Garrett G25 / G30 Class
44.8 lbs/min @ 2.45 Pr
Plot (X = 44.8 lbs/min, Y = 2.45) directly on compressor map
Corrected Mass Airflow
44.8 lbs/min (648 CFM)
0.339 kg/s engine air consumption
Pressure Ratio (Pr)
2.45 : 1 Pr
P_discharge 34.7 psia / P_inlet 14.2 psia
Turbo Match & Wheel Recommendation
Compressor Inducer Sizing:
54 mm – 58 mm Inducer Wheel
Peak Compressor Island Target:
74%–78% Efficiency Island Center
Choke / Surge Margin:
Well centered right of surge line; ample choke headroom.
Frequently Asked Questions
What is Compressor Surge and how do I avoid it?
Surge occurs on the far left of the compressor map when boost pressure is too high for the volume of air flowing through the engine. The airflow stalls across the compressor blades, reversing violently with an audible "flutter" or barking sound that destroys thrust bearings.
What does BSFC mean in turbo sizing?
Brake Specific Fuel Consumption (BSFC) measures fuel flow per horsepower per hour. Typical turbocharged gasoline engines operate around 0.50–0.55 lbs/HP·hr, while E85 requires ~0.75 lbs/HP·hr due to lower energy density.