Automotive Tools
Engine Math
Turbo Airflow & Pressure Ratio
Estimate compressor pressure ratio, CFM, mass airflow, and potential horsepower from displacement, boost, RPM, and VE.
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How to Use This Tool
- Enter engine displacement in liters or cubic inches.
- Set target boost (PSI), max RPM, and volumetric efficiency.
- Review pressure ratio and mass airflow to map compressor charts.
- Treat potential HP as an airflow-limited ceiling, not a guaranteed dyno number.
The Formula & Physics Behind the Math
Pressure ratio = (boost PSI + 14.7) ÷ 14.7. Engine CFM ≈ (CID × RPM × VE) ÷ 3456. Air density under boost ≈ 0.075 × PR lbs/ft³. Mass airflow lbs/min ≈ CFM × density. Rough power potential ≈ mass airflow × 10 HP per lb/min.
Frequently Asked Questions
What VE should I use?
Stock street engines often sit 80–90% VE. Well-ported heads and cams can exceed 100%. Start conservative if you are unsure.
Does this pick a turbo model?
No — it gives airflow targets so you can match a compressor map. Surge line, shaft speed, and efficiency islands still matter.
Is potential HP crank or wheel?
It is a flywheel-style airflow estimate before drivetrain loss, altitude, and fuel limits.