The Big Three's New Diesels put on a Dyno

RCMAN46 wrote:


This is a quote from Wikipedia on how an inertia dyno works.

Inertia Sweep: an inertia dyno system provides a fixed inertial mass flywheel and computes the power required to accelerate the flywheel (the load) from the starting to the ending RPM. The actual rotational mass of the engine (or engine and vehicle in the case of a chassis dyno) is not known, and the variability of even the mass of the tires will skew the power results. The inertia value of the flywheel is "fixed", so low-power engines are under load for a much longer time and internal engine temperatures are usually too high by the end of the test, skewing optimal "dyno" tuning settings away from the optimal tuning settings of the outside world. Conversely, high powered engines commonly complete a "4th gear sweep" test in less than 10 seconds, which is not a reliable load condition,citation needed, as compared to operation in the real world. By not providing enough time under load, internal combustion chamber temperatures are unrealistically low and power readings - especially past the power peak - are skewed to the low side.

It says nowhere in there that a dyno measures horsepower and from that, torque is derived.


The fact is that a Dyno measures the amount of torque at a given rpm and uses that to calculate horsepower. If you you don't want to believe me then take it from the very manufacturer that made the dyno in the video.

"Values Reported by a Chassis Dynamometer
A chassis dynamometer can directly measure the following values:
1. Roll shaft RPM/speed.
2. Torque/force applied to the dynamometer’s roll shaft(s).
All other values are based on these original 2 values. For example, acceleration is computed from
2 successive speed measurements, power are calculated based on the measured speed and torque
of the dynamometer’s rolls shaft(s), etc.
When a chassis dynamometer reports a “torque” value, the value reported is the torque measured
on the dynamometer’s rolls shaft(s), not on the vehicle’s drive axle or engine crankshaft. "

Page 7 - Mustang Dynamometer: Operator Manual