Todd,
Not all dynos measure torque. I don't know what dyno you use, so I can't say how yours works.
Engine dynos are set-up with an absorber unit (typically a water brake) and a torque transducer. Engine dynos measure torque through the transducer, then calculate HP. An engine dyno can load an engine and hold RPM, which is necessary for engine develpoment and testing work.
The most common chassis dyno is the Dynojet, which is an inertia dyno. Inertia dynos measure the rate of acceleration of the drum, which allows them to figure HP. Then they calculate torque backwards. Inertia dynos have a fixed roller weight (inertia weight) which approximates the weight of a vehicle. For example, if the inertia weight on a particular dyno is 600 lbs, then any vehicle on that dyno is treated as if it weighed 600 lbs, regardless of the actual vehicle weight. Some chassis dynos have an additional eddy current absorber unit added to better duplicate the actual vehicle weight, but this absober will still not allow a chassis dyno to function effectively in place of an engine dyno for testing and development.
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