[QQQ]

Wieso denn ?
Bei den MaHa-Prüfständen wird das Schleppmoment ermittelt. Damit wird über die gemessene Radleistung die Motorleistung errechnet.

Gut, geringe Messtoleranzen entstehen dadurch sicherlich, aber wer sagt mir dass wenn ich den Motor wieder einbaue und messe er dann exakt die gleiche Leistung wie auf dem Prüfstand bringt ???

Jeder Chasis Pruefstand die Radleistung in Kurbelwelle-leistung Konvertiert macht dass mit die Schleppmoment-methode (Coast down). Fazit ist aber dass auf ein chassis Dyno Radleistung gemessen wird und keine Kurbelwelle-leistung. Hier ist ein interessantes Artikel ueber chassis Dyno's: http://www.thejauntlist.org/wiley/pub/dyno.pdf

Zitiat hieraus:

The chassis dyno is an effective tool for measuring power output at the
wheels, taking into account the frictional losses inherent in the driveline. However, it must be noted that the chassis dyno has absolutely no way to
measure these driveline losses. This is where the flywheel horsepower readings derived from chassis dynos fall into the realm of misleading conjecture.

und

A chassis dyno cannot calculate flywheel h o r s e p o w e r. (Some dyno software programs will attempt this by measuring the time it takes for the rollers to spin down while the car is in gear with the clutch disengaged.) This is called a “coast-down test" and is supposedly measuring “negative horsepower" and the results (a negative number) are subtracted from the wheel horsepower results to derive flywheel horsepower. There are several problems with this method that make it unsuitable for the intended purpose. First, this coast-down test cannot measure actual frictional losses. Frictional losses are proportional to the power being fed into the driveline. This means that losses increase as the
power increases. A good reference is usually 15 percent (for manual transmission vehicles only. See sidebar). The coast-down test, however, does not reflect the power levels being fed into the driveline when wheel horsepower is being measured and therefore cannot accurately measure the amount of frictional loss. As far as the coast-down test is concerned
you could have a 400hp SVT Cobra R or a 180hp SVT Focus, the losses will be the same. Obviously the coastdown test is not measuring actual power absorption. There are a number of variables between the flywheel
and the wheels that alter horsepower results. Small variances in tire pressure can significantly change the dyno results. Wheel alignment, transmission oil temperature, tire size and gear ratio all affect the results.
It is very difficult to calculate the combined effect of so many variables, let alone do so consistently. The wheel horsepower measurements of a chassis dyno are reliable and consistent, but they are unable to accurately measure flywheel horsepower. As an engineer at Dynojet said,
“Absolutely not. Our chassis dynamometer is not capable of measuring flywheel power."