Turbo Boost & Power Gain Estimator
Estimate airflow in CFM and approximate horsepower output from a turbocharged engine based on boost pressure, displacement, volumetric efficiency, and peak RPM.
Results
What is it?
Turbo boost pressure determines how much additional air a forced-induction engine ingests above atmospheric pressure. More air means more fuel can be burned, producing more power. This calculator uses airflow (CFM = cubic feet per minute) as the intermediary � a useful figure for turbo compressor map selection.
How to use
Enter engine displacement in litres, the target boost pressure in psi (gauge pressure, as read on a boost gauge), estimated volumetric efficiency, sea-level atmospheric pressure (14.7 psi unless at altitude), and peak power RPM. The formula computes the pressure ratio, resulting airflow, and an estimated crank horsepower.
Example scenario
A 2.0L engine at 5,000 RPM with 15 psi boost, 85% VE, and 14.7 psi atmosphere: pressure ratio = (15 + 14.7) / 14.7 = 2.02. Airflow = 2.0 x 61.02 x 5000 / 3456 x 0.85 x 2.02 = 303 CFM. Estimated HP = 303 x 6.4 = ~194 HP � a rough estimate for initial turbo selection.
Pro tip
Use this result to locate the operating point on a turbo compressor map: plot your airflow (lb/min � multiply CFM by 0.069 for air density) against pressure ratio. The point should fall within the turbo's efficiency island, ideally between 70�76% efficiency. A turbo that is too small will surge; one too large will lag badly and run inefficiently.