Thread: Dyno Results
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      04-24-2008, 10:28 AM   #4
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Drives: E30 M3; Expedition
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Originally Posted by gorun View Post
Is that good, bad or about right? All these dynos are different and the they come up with 3 or 4 power readings. Just cant make sense of it...
The torque readings are pretty much in line with the results reported by RRI (see thread):

Download the detailed spreadsheet in PS and Kgm units and read the values from the Corrected Power and Corrected Torque columns, which take pressure and temp differences into account. Then compare those numbers to the corrected figures on the posted output sheet. You'll see:

Corrected Wheel Torque/Total Reduction:
RRI: 37.3 Kgm @3911 rpm
OP: 37.2 Kgm @3965 rpm

If you compare the wheel torque/total reduction readings over the entire rev range, they are in agreement, so I am assuming the OP's chart does not factor in any transmission losses for the torque reading.

However, there is something funky with the power figures. As you can see in the dissipated power reading, they are factoring in a %10 loss to "guess" engine power. If we bypass the engine reading, and just apply the temp and hum correction factor to get the standardize power reading from the 325.3hp figure, we get 335.8 peak hp.

Corrected Wheel Power:
RRI: 374.3 @7518 rpm
OP: 335.8 @7570 rpm

I don't understand why the wt numbers agree, but whp don't. I guess the wt numbers also include the 10% loss factor. In which case, the OP's numbers are about 10% off in general, which can be explained by:

1. RRI uses a hub dyno, whereas the OP used rollers.
2. OP's run was not close to steady-state (I don't know enough about the specifics of dyno run methodology to judge if a 5.8 sec run constitutes steady-state in this case).
3. Instrument differences.