Contour Enthusiasts Group Archives Forums General Dyno and Drag EH'd UIM dynoed with confusing results.

Originally posted by Ronan:

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The operator said that this figure can vary due to things such as; Tyre pressure Atmospheric pressure temp of gear oil etc. list goes on.

For accurate comparisions, he said it is best to use the figure at the flywheel. The transmission loss varies each time I go there, from 28hp to about 33hp. Hence the different readings in the whp between the two intakes despite the obvious differences in crank power...
With my EH UIM I recently got from the g/b (started life as a stock UIM) I resulted in a power drop vs. the unmodded SVT UIM from a 98 SVT. Figure that one out...

Oh, and it was the same dyno each time.

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Quote:

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did a small egr mod tonight, got a solid gasket to block off the passage of gases back into the UIM

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I'd suggested that, if possible you undo this mod for the dyno comparsion.

Did you dyno with or without the "solid gasket"?

The Ford ECU needs to have that signal. If there isn't any exhaust gas being recirculated back into the inake the computer makes adjustments on the assumption that something is wrong. The EGR, PCV, etc., systems in these cars are all monitored by the ECU and need to be functioning properly or else the computer will start adjusting the timing, etc., to compensate for the unexpected signal results. Usually resulting in a loss in power. The only way I know of to properly run without those items is with a proper "stand-a-lone" customized computer system that has been properly calibrated to the setup.

I'm also still puzzled by the the way the dyno (rolling road) operator is arriving at the results. The operator is saying it's better to use the figures at the flywheel but unless the engine is out of the car and connected to an engine dyno the only accurate figures you can get are the WHP figures. I don't see how he can ever say you've got a a 28HP loss from the transmission one day and a 33HP loss another, unless they are taking actual readings of something well beyond the scope of the dyno's I'm used to (Dynojet's - specifically the 248x).

A "chassis dyno" which measures at the wheel HP/TQ can only give you accurate figures for WHP and any mention of what the engine is making at the flywheel is an educated guess at best.

An "engine dyno" which measures at the flywheel HP/TQ is the only way to accurately tell the true HP of an engine as there are no parasitic losses such as drivetrain, etc. Unless one has done an engine dyno run and then a chassis dyno run on the same engine under the same conditions (engine temp, intake air temp, etc., etc.) then I don't think one can do anything but guess at the losses.

A proper dyno, of either type, should have probes that read atmospheric pressure, ambient air temperature, etc., and produce two sets of results. The first is the raw data and the second is the "Corrected" data. The corrected data has been adjusted to provide a figure that would be achieved at sea level at x temperature (can't remember what it is but the that's not important).

The corrected data is what should be used as it provides a constant yardstick and one should only rely on the figures that are generated from the dyno, by that I mean if it's a chassis dyno than you will have useable at-the-wheel figures.

It may be that I'm missing something here. I'm sure someone will let me know nicely , if I am , but I just don't see how the dyno operator can tell you you've got more power at the wheels than before, but less at the flywheel unless they take an accurate measurement at the flywheel. Do they actually measure anything other than the power at the wheels, temperature, pressure, etc.

Regards, Alan