How engine airflow is calculated
A four-stroke fills its displacement once every two revolutions, so:
CFM = (displacementci × RPM × VE) ÷ 3456
where 3456 = 2 × 1728 (two revs per intake stroke, 1728 in³ per ft³). Volumetric efficiency is how completely each cylinder fills: a stock engine peaks near 85–95%, a well-developed NA head can reach 100–105%, and forced induction pushes past 100% because boost crams in more than atmospheric. Mass flow (kg/min, g/s) uses standard air density and is what actually makes power — size your MAF and turbo to it.
FAQ
What VE should I use?
If you don't have a dyno-derived number: ~0.85–0.90 for a stock engine, ~0.95–1.05 for a built NA setup at peak, and 1.1–1.5+ for boosted engines depending on pressure ratio. VE also falls off away from the torque peak.
Is the power figure accurate?
No — it's a ballpark from mass airflow using a typical NA air-to-power rule. Real power depends on fuel, timing, AFR and efficiency. Use it to sanity-check airflow, not to quote numbers.