Turbo Exhaust Flow Calculator
Size a turbocharger turbine — compute exhaust mass flow, corrected flow, and A/R needed for target HP.
How to Use
- Enter target crankshaft HP and BSFC (0.55 typical for turbo gas).
- Enter AFR (11.5-12.5 at WOT under boost).
- Set pre-turbine EGT and pressure (usually 1.2-1.8 × boost + atm).
- Result gives mass flow and corrected flow vs a turbine map.
Engine target
Pre-turbine conditions
Turbine flow
Formulas
Fuel mass flow
ṁ_fuel = HP · BSFC / 60 (lb/min)
Air mass flow
ṁ_air = ṁ_fuel · AFR
Exhaust mass flow
ṁ_ex = ṁ_air + ṁ_fuel
Corrected flow
ṁ_corr = ṁ_ex · √(T₃ / 519.7) / (P₃ / 14.7)
Frequently Asked Questions
What is corrected flow?
Turbine maps plot flow corrected to a reference (519.7°R, 14.7 psi). You convert actual flow to corrected to look it up.
Typical BSFC?
NA gas: 0.45-0.50. Turbo gas: 0.55-0.65. Diesel: 0.35-0.42. Ethanol: 0.65-0.80.
Which A/R to pick?
Smaller A/R spools faster but caps top-end flow. Bigger A/R delays spool but lets high-HP live.
Common Use Cases
Turbo sizing
Cross-reference mass flow against a turbine efficiency map.
A/R selection
Choose a housing that puts your flow in the 65-70% efficient zone at peak RPM.
Divided vs open
Check whether required flow is small enough to benefit from a T4 twin-scroll.
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