Do they read HIGH or LOW?

 

Low

 

low

 

low..

 

They can read however you want them to read. Typically they read low, however I would suggest looking through David Buschur's new dyno thread. He has ordered a Mustang dyno and this was discussed in the thread.

-Paul

Edit: Here's the link: https://www.evolutionm.net/forums/sh...d.php?t=134855

 

They read all over the place. Too many shops like to "modify" there Mustang's.

 

They read "REALISTIC"....how about that.

I posted this somewhere else, but I'll post it again to clarify.

A mustang dyno uses a system in which the rollers are "loaded" at all times to simulate actual driving. What I mean by that is that they are always giving resistance in the same way a road would give resistance.

On the other hand, a dynojet does not load its rollers. It uses a large weighted drum. While this provides resistance at first, it quickly begins to build up its own intertia, meaning the car does not have to do much work itself to just keep the drum rotating, and more of the car's power goes to accelerating the drum, giving a higher HP number in the end.

Think about it this way, now. When you're driving does the road always provide resistance? Yes. The road does not start moving beneath you, it's stationary and you are moving across it. The mustang dyno simulates this, while the dynojet does not (or does very poorly)

 

Dynojet has an optional load cell, though maybe nobody uses them. But even in pure inertia mode "resistance" doesn't (or shouldn't) play much of a role. What a dynojet directly measures is time -- the time for a revolution of the drum. From that it calculates angular velocity and acceleration. Factor in the known moment of inertia of the drum and you get torque. It doesn't matter how fast the drum is spinning, it's only the acceleration that determines the torque.

Is drum inertia a "realistic" load? Not really. But there's no reason why an inertia dyno should necessarily read high unless the calibration is off or there's some optimistic "correction" going on. For a car with a big turbo it should probably read low! Most likely the inertial load is going to be less than the real load the engine sees on the road so the slew rate (rate of RPM rise during the pull) will be higher than on the road. Maybe the dynojet software does some of that correction here?

Sophisticated brake dynos can theoretically reproduce real-world loads including drag and hills and do steady-state measurements. But any dyno has to be correctly calibrated and make accurate direct measurements. There's a lot of stuff that goes on before the graph comes out!

Dave

 

As long as it is consistant it doesn't really matter what dyno you use. You could easily calibrate the Mustang dyno to read higher by applying a correction factor if you really wanted to. Drag coefficient is also not taken into account on a dyno so once you are fighting that 150MPH headwind 5th gear pull won't go nearly as fast.