Dynometers and HP
Discussion
There have been some threads on here about engine dynos and chassis dynos and the difference in HP. I found this to be an interesting read.
https://www.rbracing-rsr.com/downloads/dynojet.pdf
Stan
https://www.rbracing-rsr.com/downloads/dynojet.pdf
Stan
PeterBurgess said:
Happy New Year to you Stan, hope it is a good'un for you.
Brilliant read, thanks very much for posting it. What I really enjoy, the more it is delved into the muddier the water gets!
Still not got the Superflow up and running yet, not enough hours in the day or hands attached to my body
Last time we played we were checking the calibration, we showed 100Nm when it should be 200Nm, there is meant to be a hi/lo scale button but I cannot find it yet....maybe in the software but ran out of time!
Peter
Hi Peter,Brilliant read, thanks very much for posting it. What I really enjoy, the more it is delved into the muddier the water gets!
Still not got the Superflow up and running yet, not enough hours in the day or hands attached to my body
Last time we played we were checking the calibration, we showed 100Nm when it should be 200Nm, there is meant to be a hi/lo scale button but I cannot find it yet....maybe in the software but ran out of time!
Peter
Thank you and a Happy Year to you also. Keep at it. I am sure in the end it will be well worth it.
Stan
reggid said:
Sounds like an advert for superflow more than trying to be educational. I’m always wary of those who bash other companies to sell or push their own products.
Yes, since it is a SuperFlow document, it is going to push their good points and the others bad points. From Page 16
"Learn to use your dyno as a tool. That it what it is, regardless of who makes it. If it repeats well, it is a good tool. Learn how to keep it calibrated and how to use it when tuning an engine. Also learn which methods of testing work best for your applications and how to interpret the data. Have the company who sold you the dyno provide on-site training. Read the manual and research topics of interest on the Internet."
I think where some of the problems come from is when people try to use the numbers for something other than the above paragraph.
Stan
Pumaracing said:
It's long been known in the drag racing world that engines require different ignition advance when accelerating fast than when they are at steady state. In fact as this advance varies with the rate of acceleration there is no one single advance curve that can ever be optimum in all conditions. A simple fudge for this was to have a switch connected to the gear stick which changed the advance as the vehicle went up through the gears and the rate of acceleration dropped.
No doubt in state of the art mapping systems such as in F1 the advance curve will vary with the rate of engine acceleration on a real time basis.
If this effect is measureable for run of the mill engines you may be able to see it happen on your dyno by optimising the advance for steady state and then the fastest possible acceleration rate and seeing if there is any difference. I'd certainly be interested to know the results.
Dave,No doubt in state of the art mapping systems such as in F1 the advance curve will vary with the rate of engine acceleration on a real time basis.
If this effect is measureable for run of the mill engines you may be able to see it happen on your dyno by optimising the advance for steady state and then the fastest possible acceleration rate and seeing if there is any difference. I'd certainly be interested to know the results.
While I have not data logging from an NHRA pro Stock engine. Based on a computer simulation I get a high of a little over 9000 RPM rate of change in first gear to around 750 RM rate of change at the finish line in 5th gear.
Don't some of the high end ignition systems not only let you adjust for that but also for differences from cylinder to cylinder?
Stan
Also not all engine dyno's software does the same thing either. So you can get a different number from the same engine.
On Page 9
"What about Friction Factors and Mechanical Efficiency?"
"This question stems from the section in the SAE document that discusses how to account for the frictional power consumed by the engine and whether we should apply an atmospheric correction to that power as well as the measured brake power."
"The answer is “yes” when testing the engine on an engine dynamometer. The SAE provides several means for doing this, one of which is to basically estimate the mechanical efficiency of the engine to be ~85%; another is to actually measure the frictional losses within the engine and then add those back to the measured power before applying the correction multiplier, then subtract the frictional losses. The idea here is to apply an atmospheric correction to the total power made at the engine, not just what was left over and measured at the brake."
From a discussion sometime ago on another forum, we when over this. I had posted this.
Dyno Correction Factors
I believe SuperFlow uses ((UNCHP + FHP) * CF ) - FHP = CHP
Let say we have a 1000 BHP
Just using the CF
1000 * 1.010 = 1010
1000 * 1.110 = 1110
1000 * 1.210 = 1210
At 85% ME (1000 / .85) - 1000 = 176.47 FHP
((1000 + 176.47) * 1.010) - 176.47 = 1011.7647 diff 1.7647 HP
((1000 + 176.47) * 1.110) - 176.47 = 1129.4117 diff 19.4117 HP
((1000 + 176.47) * 1.210) - 176.47 = 1247.0587 diff 37.0587 HP
Stan
On Page 9
"What about Friction Factors and Mechanical Efficiency?"
"This question stems from the section in the SAE document that discusses how to account for the frictional power consumed by the engine and whether we should apply an atmospheric correction to that power as well as the measured brake power."
"The answer is “yes” when testing the engine on an engine dynamometer. The SAE provides several means for doing this, one of which is to basically estimate the mechanical efficiency of the engine to be ~85%; another is to actually measure the frictional losses within the engine and then add those back to the measured power before applying the correction multiplier, then subtract the frictional losses. The idea here is to apply an atmospheric correction to the total power made at the engine, not just what was left over and measured at the brake."
From a discussion sometime ago on another forum, we when over this. I had posted this.
Dyno Correction Factors
I believe SuperFlow uses ((UNCHP + FHP) * CF ) - FHP = CHP
Let say we have a 1000 BHP
Just using the CF
1000 * 1.010 = 1010
1000 * 1.110 = 1110
1000 * 1.210 = 1210
At 85% ME (1000 / .85) - 1000 = 176.47 FHP
((1000 + 176.47) * 1.010) - 176.47 = 1011.7647 diff 1.7647 HP
((1000 + 176.47) * 1.110) - 176.47 = 1129.4117 diff 19.4117 HP
((1000 + 176.47) * 1.210) - 176.47 = 1247.0587 diff 37.0587 HP
Stan
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