Turbo Size Calculator
Choosing the right turbo starts with knowing how much air your engine needs. Enter your engine displacement, target boost, and redline RPM to calculate the required airflow in CFM, the compressor pressure ratio, and a turbo frame size recommendation.
Turbo sizing is all about matching the compressor to your engine's airflow demands. An undersized turbo will hit its efficiency limits early, generating excessive heat. An oversized turbo will lag before spooling and may never reach peak efficiency on a small engine.
Key turbo sizing concepts:
- Pressure ratio: (Boost + atmospheric) / atmospheric. For 15 psi boost, that is (15 + 14.7) / 14.7 = 2.02. This is the key input for reading compressor maps.
- CFM (cubic feet per minute): The volume of air the engine needs at your target boost and RPM. Plot this against the pressure ratio on a compressor map.
- Compressor map: Every turbo has a map showing its efficiency at different flow rates and pressure ratios. You want your operating point in the middle of the high-efficiency island.
- Intercooling: An intercooler cools the compressed charge, increasing air density and power. Typical efficiency is 60-80%. Higher efficiency means denser air and more power.