Enter the engine’s base power (before boost) and either the boost pressure or the desired horsepower gain into the calculator to estimate the other. Results are approximate and depend on engine/turbo/supercharger efficiency and operating conditions.
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Formulas
There is no single, engine-independent “HP per PSI” conversion. A common rule-of-thumb estimate assumes horsepower gain is roughly proportional to the boost-to-atmospheric pressure ratio, scaled by an overall efficiency factor.
Boost to Horsepower Gain (Estimate)
HP_{gain} \approx HP_{base}\cdot \eta \cdot \frac{B}{P_{atm}}To estimate horsepower gain from boost, multiply the base horsepower by an efficiency factor (η) and by the ratio of boost (gauge) to atmospheric pressure.
Horsepower Gain to Boost (Estimate)
B \approx \frac{HP_{gain}\cdot P_{atm}}{HP_{base}\cdot \eta}- Where HPgain is the estimated horsepower increase due to boost
- HPbase is the engine power before boost (at the same RPM/conditions)
- B is the boost (gauge pressure above atmospheric), commonly in PSI
- Patm is atmospheric pressure (≈ 14.696 psi at sea level)
- η is an overall efficiency factor (often ~0.7–1.0 depending on setup)
These formulas are estimates. Real results depend on temperature, intercooling, compressor efficiency, volumetric efficiency, fueling/ignition limits, exhaust backpressure, and whether boost is sustained at the RPM/load you care about.
| Boost (PSI) | Pressure Ratio (absolute) | Ideal Power Increase (%) |
|---|---|---|
| 1 | 1.068 | 6.8% |
| 2 | 1.136 | 13.6% |
| 3 | 1.204 | 20.4% |
| 5 | 1.340 | 34.0% |
| 7 | 1.476 | 47.6% |
| 8 | 1.544 | 54.5% |
| 10 | 1.680 | 68.0% |
| 12 | 1.817 | 81.7% |
| 14 | 1.953 | 95.3% |
| 15 | 2.021 | 102.1% |
| 18 | 2.225 | 122.5% |
| 20 | 2.361 | 136.1% |
| 22 | 2.497 | 149.7% |
| 25 | 2.701 | 170.1% |
| 28 | 2.905 | 190.5% |
| 30 | 3.042 | 204.2% |
| 32 | 3.178 | 217.8% |
| 35 | 3.382 | 238.2% |
| 40 | 3.723 | 272.3% |
| 50 | 4.403 | 340.4% |
| *Pressure ratio uses Patm = 14.696 psi (1 atm). Ideal power increase ≈ 100 × (Boost / Patm). Real engines typically achieve less than “ideal” due to heating and efficiency limits. | ||
Boost Definition
Boost is the gauge pressure above atmospheric pressure in an engine’s intake manifold created by a turbocharger or supercharger. Increasing intake pressure increases the mass of air the engine can ingest, which can increase power when the engine is under sufficient load and the system is able to reach/hold that boost.
Boost to Horsepower Example
How to estimate horsepower gain from boost?
- First, determine the base engine power and an efficiency assumption.
Use the engine’s power before boost at the RPM/conditions you care about, and choose an overall efficiency factor (η) for your setup (often ~0.7–1.0).
- Next, measure boost (gauge) and estimate the gain.
Measure boost above atmospheric pressure (PSI, bar, etc.) and estimate horsepower gain using HP_gain ≈ HP_base × η × (Boost / P_atm).
Example: If an engine makes 200 HP before boost, you run 10 psi of boost, and you assume η = 0.90, then HPgain ≈ 200 × 0.90 × (10 ÷ 14.696) ≈ 122 HP, for an estimated boosted power of about 322 HP.
FAQ
Boost is the intake manifold pressure above atmospheric pressure (gauge pressure) created by a turbocharger or supercharger. Higher boost can increase power by increasing the mass of air entering the engine, but the actual horsepower gain depends on the engine and the system’s efficiency.