Turbocharger Boost Pressure Calculator
Calculate turbocharger boost pressure, pressure ratio, and estimated power gain.
Convert between psi, bar, and kPa boost.
Estimate compressor outlet temperature and intercooler needs.
What Is Boost Pressure? Boost pressure is the pressure above atmospheric that a turbocharger or supercharger delivers to the engine. Standard atmospheric pressure: 14.696 psi = 1.01325 bar = 101.325 kPa at sea level. “10 psi of boost” means the intake manifold pressure is 10 psi above atmospheric = 24.7 psi absolute. Turbochargers work by compressing intake air — more air = more fuel = more power.
Pressure Ratio Pressure ratio (PR) = absolute manifold pressure / atmospheric pressure PR = (boost_psi + 14.696) / 14.696 Typical stock turbos: PR 1.4–2.0. Modified: 2.0–3.5. High-performance: 3.5+. The pressure ratio determines how much the air is compressed, and therefore how much its temperature rises.
Compressor Outlet Temperature Hot compressed air is less dense and prone to detonation — hence the intercooler. Ideal gas compression: T₂ = T₁ × PR^((γ−1)/γ) For air (γ = 1.4): T₂ = T₁ × PR^0.2857 (temperatures in Kelvin) Actual temperature is higher due to compressor inefficiency (η_c = 70–80% typical). T₂_actual = T₁ + (T₂_ideal − T₁) / η_c
Power Gain Estimate Simple estimate: Power gain ≈ (PR − 1) × naturally aspirated power × volumetric efficiency factor More accurate: compare trapped air mass with atmospheric (accounting for intercooler and density). Naturally aspirated engines: ~1 hp per 14.7 psi (atmospheric) of displacement. Each additional 14.7 psi of boost roughly doubles the air mass → doubles potential fuel/power.
Intercooler Intercoolers cool compressed air before it enters the engine. Cooler air is denser — more air per stroke = more power. Intercooler efficiency: temperature drop as fraction of maximum possible. At PR = 2.0, outlet temp without intercooler: ~85°C (185°F) above ambient. With a good intercooler (75% efficiency), temp rise above ambient: ~21°C.
Detonation Risk Higher boost + higher compression ratio = higher detonation risk. Rule of thumb: reduce static compression ratio by 1 point per 5 psi of boost. For 10 psi: reduce from 9:1 to 7:1 compression, or use higher octane fuel. Premium (91 octane) vs E85 (105 octane): E85 allows significantly more boost.