NA to Boosted HP Calculator
Estimate horsepower after adding a turbo or supercharger to an NA engine.
Adding a turbocharger or supercharger forces more air into the engine, raising horsepower roughly in proportion to the pressure ratio. This calculator estimates the new power from your naturally aspirated baseline and target boost.
NA to Boosted Formula
The pressure ratio compares total manifold pressure (atmospheric + boost) to atmospheric alone. Real gains fall a little short of the theoretical figure because compressing air heats it, reducing density — which is why intercooling matters.
How to Use This Calculator
- Enter your NA horsepower.
- Enter target boost in PSI.
- Read the estimated boosted horsepower.
Worked Example
How the Pressure Ratio Drives Power
Forced induction makes power by raising the absolute pressure in the intake manifold. The pressure ratio is (atmospheric + boost) ÷ atmospheric, and since power scales nearly with the air mass ingested, that ratio is roughly the power multiplier. At 14.7 PSI of boost you double atmospheric pressure (a 2.0 ratio), which is why power almost doubles in theory.
Why Real Gains Are Lower
Compressing air heats it, lowering its density, so an intercooler is essential to recover power. Turbine backpressure, ignition timing pulled to prevent knock, and the engine's volumetric efficiency all trim the theoretical figure — typically by 10–20% on a street tune. Turbochargers use exhaust energy (some lag, big top-end), while superchargers are belt-driven (instant, but consume crank power).
Estimated Boosted HP (300 NA baseline)
| Boost (PSI) | Pressure ratio | Est. HP |
|---|---|---|
| 6 | 1.41 | ~380 |
| 8 | 1.54 | ~417 |
| 12 | 1.82 | ~490 |
| 16 | 2.09 | ~565 |
Frequently Asked Questions
Roughly in proportion to the pressure ratio: HP × (14.7 + PSI) ÷ 14.7. About 8 PSI can add 40–50% power, minus a small loss to charge heat.
Compressing air heats it, lowering its density. Without effective intercooling, real gains fall a bit short of the pressure-ratio estimate.
Turbos are more efficient and often make more peak power; superchargers give instant response. Both follow the same pressure-ratio physics.
Usually yes — fuelling, often lower compression, and stronger internals at higher boost levels, plus tuning to keep the air-fuel ratio safe.
It depends entirely on the engine, fuel, and build. Low boost (5–8 PSI) is common on stock-ish engines; high boost needs forged internals and careful tuning.