340 on dyno video, whats your opinion

MOPEkidD-3 said

I suppose so? lol... Just thinking out loud about how a water brake engine dyno works (at least the ones I've seen), the "torque" is measured simply by a strain gauge (force sensor) sensing how hard the turbine housing is being pressed against its stop by the rotation of the engine. The maximum force will occur when the engine is fully loaded at steady RPM but once that load is lightened to let the RPMs increase, the mutual force of the engine trying to push the dyno vs. the dyno trying to slow down the engine also goes down. So yes the torque output of the engine doesn't change but the way it's being measured does...?

Click to expand...

OK, makes sense; that linear strain gauge, mounted so far from the axis of rotation, can be used to compute the drag (reverse torque) that the housing/dyno load is exerting on the engine. At steady state RPM, the dyno drag equals the steady state engine torque.

When the dyno is partially 'unloaded', it is set so that the lower housing torque relates to a certain lower dyno drag (reverse torque) against the engine. Then it measures how fast the engine accelerates over time. In the computations, it can compute that if the system accelerated so many RPM in so many milliseconds, then the engine's torque had to exceed the dyno drag by so many ft-lbs. So it can add that excess torque to the (hopefully well) known drag of the dyno, and say that the engine's torque is that sum.

The strain gauge accuracy versus actual drag for various drag settings, time measurement accuracy, rpm measurement accuracy, rotational mass that absorbs differing energy levels versus RPM and which has to has to be calibrated out, and computation errors can all contribute to this being off.