340 on dyno video, whats your opinion

nm9stheham said
Mmmmm, not quite the case: the torque from the engine does not change when the acceleration starts. Maybe you meant to say the drag from the dyno goes down?

  • When it is at a steady RPM, the dyno load's drag (reverse torque, if you will) presented to the engine equals the engines torque; there is net zero torque, and so the system does not change speed.
  • When the load's drag is reduced to start the 'run', the engine torque (input torque to the dyno) does not change at that moment, and now exceeds the drag, so you end up with net 'positive' torque in the system that accelerates everything.
Yes, steady state loads take a lot of errors out, particular time related errors.
Click to expand...

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...?

This is why dynos are useless IMO for telling you how powerful your engine is, that's what drag strips are for. I'd much rather use vehicle weight and trap speed to find HP. Dynos help visualize how and where your engine makes power and what it likes as far as tuning goes but that's about it; there are multiple layers of calculations and measuring used in the dyno process that leave tons of room for errors or numbers-fudging.

To the OP: it happens time and again on here where someone will post numbers from a dyno run complaining they are too low (nobody's upset when they're too high, until they hit the race track lol) but they don't realize that it means nothing. If your car weighs 3400 lbs and hits 100 MPH at the end of a 1/4-mile that IS your power, doesn't matter if a dyno says the wheels are putting down 200 or 900 HP at the end of the day all that matters is how quickly that engine can accelerate a mass from a stop.