How to read a dyno graph
Power and torque, wheel and crank, correction standards: what the graph you get after a remap really shows — and why a comparison only makes sense on the same dyno.
After every remap we give you the graph of the before and after runs. At first glance it is a few curves and a couple of numbers in a corner. If you know what you are looking at, though, it says a lot about how the car will behave on the road.
Two curves: torque and power
Torque (Nm) is the twisting force the engine delivers at each rpm. It is what you feel when you press the throttle on a hill or overtake in fifth gear.
Power (PS or hp) is torque multiplied by engine speed. In metric units: power (PS) = torque (Nm) × rpm ÷ 7,023. That is why power usually keeps rising even after torque has started to fall: revs increase faster than torque decreases.
The two are not independent. They are two views of the same measurement.
Look at the shape, not just the peak
Peak power is the number people talk about, but everyday driving happens mostly in the mid-range. On the graph, check:
- Where torque builds. On a turbo engine, a curve that rises earlier means less waiting when you press the pedal.
- How wide the plateau is. Torque that stays high over a broad rev range makes a car more flexible than a sharp peak.
- How smooth the curves are. Spikes or sudden dips can point to a problem with fuelling, ignition or boost control.
- How the curve ends. Power that fades abruptly at high revs can mean something is restricting the engine — a filter, temperature or a factory protection.
With before and after curves on the same graph, you can see exactly where you gained. Often the biggest difference is in the middle, not at the peak.
Wheel or crank?
The dyno measures force at the wheels. Between the engine and the road there are the gearbox, differential, driveshafts and tyres, which absorb part of the power. Manufacturers, however, quote power at the crank.
To compare a measurement with factory figures, the dyno calculates drivetrain losses — usually during the coast-down after the acceleration run, when the car rolls without throttle. The engine power you see is therefore a calculation based on the wheel measurement. It is very useful for comparison, but it is not the same as an engine test-bench measurement.
Correction standards
Air is not the same every day. In heat, low barometric pressure or humidity the engine gets less oxygen and makes less power. To compare runs from different days, results are corrected to standard conditions using a standard such as DIN 70020, EEC 80/1269, ISO 1585 or SAE J1349.
Each standard uses slightly different reference conditions, so the same car will not produce exactly the same number under all of them. A serious graph states which standard was used. If it doesn't, or if the correction factor is unusually large, treat the number with caution.
Why before and after on the same dyno
Two different dynos — even from the same manufacturer — can give different figures for the same car: different calibration, strapping, tyre pressures, room temperature. That is why comparing "factory figure from the brochure" with "remapped on some dyno" says little.
What matters is the difference between two runs on the same machine, with the same procedure, on the same day. On our own 4WD Dimsport dyno repeatability is in the order of 1–2 PS, so the difference you see is real and not measurement noise. Because it is all-wheel drive, rated up to 800 PS per axle, we also measure 4x4 cars the way they drive on the road.
The first run has diagnostic value too: if a standard car is making noticeably less than it should, we look for the cause before writing anything.
The takeaway
A good graph shows torque and power, before and after, from the same dyno, with the correction standard stated. Look at the shape of the curves first and the peak second.
Want to see what your own car could deliver? Start with the car finder or request a quote.