Turbo Boost Horsepower Gain Calculator

How it is calculated

Power is assumed to scale with the absolute air pressure in the intake. boosted hp = NA hp × (14.696 + boost) / 14.696, where NA hp is the naturally aspirated power, boost is the gauge pressure in psi, and 14.696 psi is standard atmospheric pressure at sea level. gain = boosted hp − NA hp and gain % = boost / 14.696 × 100. The percentage gain depends only on the boost, so 7 psi always gives 47.63%, whatever the engine. Horsepower is rounded to whole numbers. Both inputs must be above zero, so a boost of 0 gives no result, and a boost above 150 psi is also rejected as beyond any real turbo setup. The method ignores intercooler losses, fuel, ignition timing and the drop in atmospheric pressure at altitude, so real gains are usually lower; treat the figure as a ceiling.

Common mistakes

• Entering boost in bar or kPa. The field is in psi; 1 bar is about 14.5 psi, so typing 1 for a 1 bar turbo underestimates the gain by a large margin.
• Entering absolute pressure (for example 21.7) instead of gauge pressure. The tool adds atmospheric pressure itself, so enter only the boost above atmosphere.
• Entering the engine's rated power at the wheels or with the current turbo. The base must be the naturally aspirated figure of the engine.
• Treating the result as a promise. The figure is a theoretical ceiling; intercooler heat, fuel supply and timing usually remove some of the gain.
• Using a boost of 0 to check the baseline. Both fields must be above zero, so it returns nothing.