Calculators · Engine
Engine airflow and volumetric efficiency calculator
An engine is an air pump: the power it can make is limited by how much air it moves. These calculators estimate the airflow an engine needs at a given speed, work out its volumetric efficiency from a measured airflow, and estimate how much power a given airflow can support. They are the starting point for sizing throttle bodies, mass airflow sensors, intakes and turbochargers.
Airflow required by an engine
Estimates the volume and mass of air a four-stroke engine consumes at a given speed. Volumetric efficiency accounts for how well the cylinders fill, and boost raises the air density entering the engine.
Q = V_d × (rpm / 2) × VE × (P_atm + boost) / P_atm ṁ = Q × ρ_air
Volumetric efficiency from measured airflow
Compares the airflow an engine actually draws — for example from a mass airflow sensor log — with the theoretical maximum for its size and speed. Values near or above 100% indicate an efficient or forced-induction engine.
VE = ṁ_measured / (V_d × rpm / 2 × ρ_air)
Power supported by an airflow
Estimates the power a given airflow can support, from the air–fuel ratio and the engine’s brake-specific fuel consumption. It is an estimate — real results depend on how efficiently the engine turns fuel into work.
ṁ_air = Q × ρ_air, ṁ_fuel = ṁ_air / AFR P = ṁ_fuel / BSFC
Worked example: a 2.0-litre engine at 6,000 rpm
- Each cylinder fills once every two revolutions: 1.998 L × 3,000 = 5,994 L/min at 100% VE.
- At 90% VE: 5,394 L/min = 5.39 m³/min, or about 190 CFM.
- Mass flow: 5.39 m³/min × 60 × 1.184 kg/m³ = 383 kg/h.
- With 1 bar of boost the same engine moves roughly twice the air: about 10.8 m³/min.
Typical volumetric efficiency at peak torque
| Engine type | Volumetric efficiency |
|---|---|
| Two-valve naturally aspirated | about 75 – 85% |
| Four-valve naturally aspirated | about 85 – 95% |
| Racing naturally aspirated (tuned intake and exhaust) | about 100 – 110% |
| Turbocharged or supercharged (relative to ambient) | about 130 – 250% |
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About these results
Results are theoretical estimates from standard engineering formulas. Real-world figures depend on conditions these formulas do not capture. Always follow the manufacturer's specifications for maintenance, loading and safety decisions.
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