How the US tune comparison works
Absolute change = after measurement − before measurement. Percentage change = absolute change ÷ before measurement × 100. Each before figure must be positive so that its percentage has a defined baseline. A zero after figure is accepted; it represents a complete loss of the entered measured output. Negative changes are shown as losses, rather than being forced to zero.
Power and torque are compared separately. Their peak readings may occur at different engine speeds, so the calculator does not infer one peak from the other. The measurement-basis selector records whether both readings are at the wheels or at the engine; it applies no drivetrain-loss correction.
Worked US dyno example
Before and after readings of 250 and 300 hp give a power gain of 50.00 hp, or 20.00%. Torque readings of 280 and 336 lb-ft give a gain of 56.00 lb-ft, also 20.00%. The after power converts to 223.71 kW. These are hypothetical measurements, not a promised tune result.
Making a meaningful before-and-after comparison
Use readings from comparable tests of the same vehicle, with the same measurement basis and atmospheric correction standard. Dynojet explains that correction factors adjust power and torque for atmospheric conditions. COBB notes that the dynamometer, tyre or tire pressure, strapping and weather can affect the measurement; its comparison method uses averages of repeated pulls. Enter your prepared comparable averages when available.
A positive percentage alone does not establish reliability, emissions compliance, fuel economy or safe drivetrain loading. This page does not look up a vehicle registration, apply a Stage 1 or Stage 2 uplift, estimate a tuning price, draw an invented dyno curve or predict acceleration. Ask the testing operator to explain mismatched sheets before comparing them.
US power and torque conventions
The base power unit is mechanical horsepower (hp), and torque is in pound-feet (lb-ft). Keep wheel horsepower and engine horsepower on the same basis in both tests. A European sheet marked PS uses metric horsepower; use its converter instead of treating PS and mechanical hp as identical.
The inline controls preserve the physical quantity when converting kW, PS, Nm or lb-ft into the local base unit, retaining six decimal places. Mechanical horsepower is about 0.745699872 kW, metric PS is 0.73549875 kW and a pound-foot is about 1.355817948 Nm. Electrical and boiler horsepower are excluded.
For the other local units and terminology, use the UK remap calculator.
To measure fuel economy from fill-up records, use the US MPG calculator.
Inputs for the US remap calculator
Measurement basis
Choose one basis used by both sets of readings. Mixing engine and wheel measurements gives a misleading comparison.
Power before remap
Enter the positive before power reading in hp, or convert from kW or PS. Match the measurement basis and correction standard.
Power after remap
Enter the zero-or-positive after power reading in hp, or convert from kW or PS. Match the measurement basis and correction standard.
Torque before remap
Enter the positive before torque reading in lb-ft, using the same basis and correction standard. The unit control converts Nm.
Torque after remap
Enter the zero-or-positive after torque reading in lb-ft, using the same basis and correction standard. The unit control converts Nm.
CALCULATOR QUESTIONS
US remap calculator questions
Will this predict a Stage 1 or Stage 2 gain?
No. You must supply measured before-and-after figures. There is no universal gain percentage that applies to every engine, tune and test setup.
Can I compare wheel power with engine power?
Use the same basis in both measurements. The selector labels the comparison and does not estimate transmission losses.
Why is my percentage negative?
The after reading is lower than the before reading. That is a measured loss relative to your entered baseline; check the comparability of the tests before drawing conclusions.
Are PS and bhp or hp the same?
Metric horsepower (PS) and mechanical horsepower have different definitions. Use the PS converter so the comparison uses a consistent unit.