Calculators · Forced induction
Turbocharger airflow and power calculator
Choosing a turbocharger starts with two numbers: how much air the engine needs, and at what pressure ratio. Compressor maps plot exactly these. These calculators estimate the air mass flow a boosted engine consumes, the power a given airflow can support, and the temperature of the air leaving the compressor, which decides how much work the intercooler has to do.
Air mass flow of a boosted engine
Calculates the mass of air a four-stroke engine consumes from its size, speed, volumetric efficiency, boost and intake temperature. Mass flow is what a compressor map’s horizontal axis shows, usually in lb/min.
ρ = P_abs / (R × T) ṁ = V_d × (rpm / 2) × VE × ρ
Power supported by compressor airflow
Estimates engine power from compressor air mass flow using the air–fuel ratio and brake-specific fuel consumption. A common rule of thumb is about 10 hp per lb/min of air for a petrol engine; this calculator shows where that figure comes from.
fuel [lb/h] = air [lb/h] / AFR hp = fuel / BSFC
Compressor outlet temperature
Compressing air heats it. This estimates the air temperature leaving the compressor from the inlet temperature, pressure ratio and compressor efficiency read from the map. Hotter air holds less oxygen, which is why intercoolers are used.
T₂ = T₁ × (1 + (PR^0.2857 − 1) / η) (kelvin)
Worked example: turbocharging a 2.0-litre engine
- At 1 bar boost and 45 °C, air density is 201,325 / (287.05 × 318.15) = 2.20 kg/m³.
- At 6,000 rpm and 95% VE the engine inhales 5.69 m³/min: 12.55 kg/min, or 27.7 lb/min.
- 30 lb/min at AFR 11.5 and BSFC 0.55 supports about 285 hp.
- At a pressure ratio of 2.0 and 72% efficiency, 25 °C air leaves the compressor at about 116 °C.
Compressor outlet temperature at 72% efficiency, 25 °C inlet
| Pressure ratio | Outlet temperature | Temperature rise |
|---|---|---|
| 1.5 | about 76 °C | about 51 °C |
| 2.0 | about 116 °C | about 91 °C |
| 2.5 | about 149 °C | about 124 °C |
| 3.0 | about 178 °C | about 153 °C |
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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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