Boost to Horsepower
What a turbo or supercharger could make from your NA baseline - shown as the rough planning estimate it honestly is, never as one exact number.
Enter Engine and Boost Details
100% is the loss-free ideal. Published guidance puts sorted, well-intercooled setups 10 to 15 percent below it (85 to 90). Hot or restrictive setups run lower.
Boosted Power Estimate
Power at each boost level
| Pressure ratio |
|---|
Power versus Boost Chart
Hit a target power?
What the formula does
An engine is an air pump, and power tracks airflow. Boost raises the absolute pressure feeding it: the pressure ratio is (boost + 14.7) / 14.7, the same definition Garrett uses for turbo sizing, with 14.7 psi being sea-level atmosphere. Loss-free, power scales with that ratio; the efficiency slider then discounts the added power, so at zero boost the estimate correctly returns your NA baseline. The widely published worked example - 200 hp, 8 psi, 80% efficiency, giving 287 hp - reproduces here with the slider at 80. Some calculators multiply the whole result by the efficiency instead of just the gain; that convention reads slightly lower and shows a nonsense power loss at zero boost. The 14.7 itself is a sea-level number: ambient pressure falls by roughly half a psi per 1,000 ft of altitude, cutting both the NA baseline and the pressure ratio - one reason mountain dynos read low and turbo cars feel altitude less than NA cars do.
Choosing the efficiency factor
The slider is where all the physics this formula skips gets paid for. Compressing air heats it, and hot air is thin air - a good intercooler claws most of that back, a missing one does not. Exhaust backpressure from the turbine costs pumping work. Published guidance puts well-sorted setups 10 to 15 percent below the ideal gain; a hot, restrictive, or non-intercooled build belongs lower, and a positive-displacement supercharger loses additional crank power to the drive belt that no slider position can honestly represent. When in doubt, quote the range, not the number.
What it cannot tell you
Whether the fuel system keeps up - the injector size calculator will size injectors and BSFC for the new number. Whether the engine survives it - boosted builds run lower static compression for knock margin, which the compression ratio calculator covers. Whether the turbo can actually deliver that airflow at that pressure - that is a compressor map question, not a formula question. And whether the result reaches the ground: when the build is done, a quarter mile trap speed through the trap speed calculator is the honest way to check what really showed up.