How Much Horsepower Is 5 psi of Boost?

About 5 psi of boost typically translates to roughly a 30–35% theoretical horsepower increase at sea level, with real-world gains more commonly in the 15–30% range depending on intercooling, fuel quality, tuning, and whether you’re using a turbocharger or a supercharger. For example, a 200 hp naturally aspirated engine might see an ideal 268 hp, but a well-tuned, intercooled turbo setup often lands closer to 240–260 hp at 5 psi.

What 5 psi Actually Means

Boost is pressure above atmospheric. Power potential scales with absolute manifold pressure, not just the gauge psi. At sea level, atmospheric pressure is about 14.7 psi. Add 5 psi of boost and the intake manifold sees ~19.7 psi absolute. In ideal terms (perfect efficiency, no temperature penalties), power scales by the ratio of absolute pressures.

The simple relationship is: HP_boosted ≈ HP_NA × [(P_atm + Boost) / P_atm] × η, where η captures real-world effects such as compressor efficiency, intercooler effectiveness, fuel/ignition limits, and, for superchargers, parasitic drive losses.

The Quick Math

Ideal case at sea level

At P_atm ≈ 14.7 psi and Boost = 5 psi: pressure ratio = 19.7 / 14.7 ≈ 1.34. That’s an ideal gain of about +34% horsepower. If an engine makes 200 hp naturally aspirated, the theoretical ceiling is ~268 hp before accounting for heat, tuning, or mechanical losses.

At elevation

At ~5,000 ft, P_atm ≈ 12.2 psi. With 5 psi of boost: pressure ratio = (12.2 + 5) / 12.2 ≈ 1.41, or ~+41% ideal. Because a boost gauge reads relative to local atmospheric pressure, 5 psi at altitude targets a similar relative mass-flow increase, but the compressor works harder and intake temperatures often run higher, trimming real gains.

Real-World Outcomes

Engines rarely achieve the ideal percentage because compressing air adds heat, which reduces density and may force conservative ignition timing on pump gas. Intercooling helps, but practical efficiency and, in the case of superchargers, belt-drive parasitic losses bring the gains down from the theoretical 34% at sea level.

The following factors explain why results vary by setup and fuel:

• Intercooling effectiveness: better cooling preserves air density and detonation margin.
• Fuel octane and tuning: higher octane and optimized timing approach ideal gains; pump gas with conservative timing reduces them.
• Compressor/turbo efficiency: higher efficiency means less heat for a given pressure ratio.
• Exhaust backpressure (turbos): high drive pressure can limit airflow and raise charge temps.
• Parasitic load (superchargers): belt-driven units can consume 10–30+ hp even at 5 psi.
• Engine baseline VE/cams/compression: naturally efficient engines respond strongly to mild boost; marginal VE may limit gains.
• Ambient conditions and heat soak: hot weather and sustained pulls increase intake temps and reduce power.

Taken together, these variables typically yield 15–30% gains for intercooled turbo systems on pump gas at 5 psi, while positive-displacement or centrifugal superchargers often deliver slightly less net gain due to drive losses.

Worked Examples

These scenarios illustrate how to estimate horsepower with 5 psi, contrasting ideal math with realistic outcomes for common setups.

1. 200 hp NA engine, intercooled turbo, sea level: Ideal 200 × 1.34 ≈ 268 hp. Likely 240–260 hp with good tuning on 91–93 octane.
2. 200 hp NA engine, supercharger, sea level: Ideal still 268 hp, but subtract parasitic losses; likely 230–255 hp depending on blower type and pulley size.
3. 400 hp NA engine, intercooled turbo, sea level: Ideal ~400 × 1.34 ≈ 536 hp. Likely 480–520 hp on pump gas; more with ethanol or race fuel.

These ballparks assume healthy engines and competent calibration. Ethanol blends (E30–E85), efficient intercooling, and optimized ignition can move results closer to the ideal; poor cooling or conservative tunes push them lower.

Practical Notes

Think of boost as a percentage multiplier rather than a fixed horsepower amount. The clean way to estimate is to multiply your naturally aspirated horsepower by the absolute pressure ratio, then adjust for efficiency and losses. If you don’t know the efficiency details, assume roughly 0.85–0.95 overall for a well-intercooled turbo at 5 psi and 0.75–0.90 for a supercharger after accounting for belt load, then compare to your ideal figure.

Summary

Five psi of boost corresponds to an ideal ~34% power increase at sea level, but most real-world builds see 15–30% depending on intercooling, fuel, tuning, and hardware. Use the formula HP_boosted ≈ HP_NA × [(P_atm + Boost) / P_atm] × η, and expect turbo systems to land closer to the ideal than belt-driven superchargers at the same boost due to lower parasitic losses.

How much HP does 10 PSI of boost add?

There’s no exact horsepower (hp) amount for 10 psi of boost, as the power increase is highly dependent on the engine’s baseline horsepower, turbo efficiency, engine modifications, and other factors. However, you can estimate it using a general rule of thumb, such as a roughly 68% increase for a 350 hp engine, or roughly 20 hp per pound of boost. 
How to Estimate Horsepower Gains

• Use a percentage increase: Opens in new tabA commonly cited rule of thumb is that one atmosphere (about 14.7 psi) of boost could double an engine’s horsepower, meaning an additional 14.7 psi would give you about a 100% increase. 
• Use the “10 hp per psi” rule of thumb: Opens in new tabAnother approximation is that 1 pound of boost equals about 10 hp. 
• Consider your base engine’s horsepower: Opens in new tabFor example, if your engine produces 200 hp, and you add 10 psi of boost (using the 10 hp per psi rule), you could estimate an additional 100 hp, for a total of 300 hp, according to Reddit users. 
• Consider a more accurate percentage: Opens in new tabUsing a slightly more precise calculation based on the 14.7 psi rule, 10 psi of boost might provide about a 68% increase, says MotorTrend. So, a 350 hp engine could theoretically gain 238 hp, bringing the total to 588 hp. 

Factors Affecting Horsepower Gains

• Engine size and type: Opens in new tabLarger and more efficient engines, like V10s, naturally benefit from boost differently than smaller four-cylinder engines. 
• Turbocharger efficiency: Opens in new tabNot all turbos are equal. More efficient turbos produce more power with less boost. 
• Engine modifications: Opens in new tabOther modifications, such as a more efficient intercooler or increased compression, can significantly impact the final output. 
• Intake air temperatures: Opens in new tabBoost increases air temperature, which reduces engine efficiency and can impact performance. 
• Engine tuning: Opens in new tabProper tuning is crucial to take full advantage of the added boost without damaging the engine. 

The only way to get the exact horsepower is with a dynamometer: A dyno is a device that can accurately measure a car’s horsepower and torque.

How much HP does Boost add?

General rule of thumb is 25hp per pound of boost.

How do you convert PSI to hp?

HP = PSI × GPM ÷ 1,714
Both formula give the same answer.

How much HP will 5 PSI add?

Adding 5 PSI of boost to atmospheric 14.7 PSI, you get about a 34% increase in oxygen (19.7 PSI vs 14.7 PSI), or you would do roughly 260 HP in an engine that made 200 HP beforehand.