From our own experience we can report that not every dynamometer indicates the real power.
Often, too low air mass flows for cooling the charge air lead to unwanted control interventions by the engine electronics, resulting in lower torque and thus lower performance.
Vehicles like an RS4 B5, for example, are usually run in 5th gear on a dyno. At nominal speed, a speed of approx. 250 km/h is achieved. The cooling air that flows out of the blower in front of the vehicle often does not reach these high speeds. This results in a higher temperature of the charge air than on the road.
With several measurements in succession, it can then often be seen that the peak power becomes lower and lower. Long pauses between measurements or intercoolers wetted with water bring relief, but do not solve the problem.
So why not measure on the road/highway? Where you have constant and real environmental conditions!
Until now, there has been no reliable, reproducible way to measure vehicle power and torque on the road.
The inaccuracy displayed by the measuring equipment leads to high scatter in the results. Various systems use a location definition across multiple satellites and a change in position measured with a high sampling and can then convert to acceleration by changing time and to power using weight and other parameters. However, the results of these measurements scatter relatively strongly, since each measurand entails a measurement error and the addition of the errors can then account for a large proportion.
The insoric RealPower measures the change in wheel speed when accelerating in a defined gear with a sampling of 10 Hz, i.e. 10 times per second. Using the measured values of wheel diameter, vehicle weight, air pressure and outside temperature, the system can calculate the torque and power and then correct them according to EWG or DIN to establish comparability with other measurement systems. To measure the power at the engine, i.e. at the crankshaft, an acceleration from just above idle speed to the rev limiter and a subsequent coasting at idle speed must be performed. During acceleration, the forces at the wheel are calculated and during coasting, the so-called drag power, i.e. all resistances such as aerodynamics, rolling friction of the tires, resistances of the drive shafts and in the transmission are added. These two values are added together and result in the power output of the motor.
This measurement methodology allows reproducible measurement results with relatively little effort.
This post is also available in: French German Italian Spanish