How to read a dyno sheet

The example is a Mercedes-Benz E55 AMG with the M113K supercharged 5.4 V8, measured on the Dynojet 224xLC. The whole session, all three pulls, is on the results page if you want to follow along.

Torque is the twisting force the engine makes. Power is the rate at which it does work, and it is derived from torque and engine speed, not measured separately. On an imperial sheet the relationship is exact: horsepower equals torque multiplied by rpm, divided by 5,252.

That constant has a consequence worth knowing, because it is the fastest way to spot a fabricated graph. Since the two are the same quantity at 5,252 rpm, the curves must cross there. Every honest sheet drawn in those units crosses at that point. If one does not, the graph has been drawn rather than measured.

On this sheet torque peaks at 586.92 lb-ft at 3,240 rpm, while power peaks much later at 510.64 hp at 5,620 rpm. The gap between those two numbers is the character of the engine.

Torque arriving low and staying flat across a wide band is what a positive displacement supercharger does: it is driven off the crank, so boost climbs with engine speed rather than waiting on exhaust energy to spin something up. A turbocharged engine of similar output would show a later, steeper rise.

SAE 1.05 is the standard here. Correction adjusts the measured result to a reference day so that a pull in August and a pull in February can be compared at all. It is not a way of inflating a figure, and the raw conditions are printed alongside precisely so you can see what was adjusted.

Air temperature, barometric pressure and relative humidity are on the sheet because they change the result. This session ran at 91.62 degrees Fahrenheit, 29.44 inHg and 61.47 percent humidity. Hot, humid, low pressure air holds less oxygen, so the same engine makes less on a summer afternoon than on a cold morning.

If a sheet has no conditions on it, you cannot tell whether a figure was flattered by the weather, and you certainly cannot compare it with anything.

A chassis dyno measures at the roller, which means everything between the crankshaft and the tyre has already taken its cut: gearbox, driveshaft, differential, bearings, tyre deformation. The figure on the sheet is what actually reaches the road.

Some shops apply a drivetrain loss estimate and quote a crank number instead. That is an assumption printed as a measurement, and it is why the same car can be advertised two different ways. We publish what the machine read. There is more on that in wheel horsepower versus crank horsepower.