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
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
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
Even taking away the ad for Superflow, it makes interesting reading. I must admit though, I prefer the inertia testing as I cannot help but feel cars are either accelerating or cruising but not holding exact rpm at wide open throttle. Seems to work for us as we have been able to improve acceleration out of bends since we have had the inertia rollers. We use the pau to hold full load to make sure we are not detonating after we have done the inertia tuning.
Peter
Peter
I'm not really clear about the "missing" horsepower the Dynojet engineers were supposedly unable to find. It appears simply to be the difference between wheel and flywheel bhp which of course all of them would have understood perfectly well and known that a chassis dyno could never produce flywheel numbers. However it seems Dobeck ordered a fudge factor to be built in that DID make the dynos produce something close to flywheel numbers. A very weird decision if the story is true.
The story seems to be implying a stupidity on the part of the Dynojet engineers that can't have existed and as such is rather "over egging the cake" so to speak. This hyperbole does indeed make it look more like a Superflow advert than any honest critique of what actually happened at Dynojet in the 80s.
The story seems to be implying a stupidity on the part of the Dynojet engineers that can't have existed and as such is rather "over egging the cake" so to speak. This hyperbole does indeed make it look more like a Superflow advert than any honest critique of what actually happened at Dynojet in the 80s.
PeterBurgess said:
Even taking away the ad for Superflow, it makes interesting reading. I must admit though, I prefer the inertia testing as I cannot help but feel cars are either accelerating or cruising but not holding exact rpm at wide open throttle. Seems to work for us as we have been able to improve acceleration out of bends since we have had the inertia rollers. We use the pau to hold full load to make sure we are not detonating after we have done the inertia tuning.
Peter
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.Peter
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.
More of a thing to play with on the engine dyno methinks and see if timing does vary depending on static load or fast runs with min time twixt loads. Even though it would seem bhp on the dyno is higher under static load than transient load cos of inertia it is a matter of getting best bhp from either method.
Peter
Peter
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
Pumaracing said:
I'm not really clear about the "missing" horsepower the Dynojet engineers were supposedly unable to find. It appears simply to be the difference between wheel and flywheel bhp which of course all of them would have understood perfectly well and known that a chassis dyno could never produce flywheel numbers. However it seems Dobeck ordered a fudge factor to be built in that DID make the dynos produce something close to flywheel numbers. A very weird decision if the story is true.
The story seems to be implying a stupidity on the part of the Dynojet engineers that can't have existed and as such is rather "over egging the cake" so to speak. This hyperbole does indeed make it look more like a Superflow advert than any honest critique of what actually happened at Dynojet in the 80s.
i reread it and apparently there was a discrepancy even after driveline losses were accounted for. i interpreted it as though they were just trying to fudge the unknown drivetrain inertia into it.The story seems to be implying a stupidity on the part of the Dynojet engineers that can't have existed and as such is rather "over egging the cake" so to speak. This hyperbole does indeed make it look more like a Superflow advert than any honest critique of what actually happened at Dynojet in the 80s.
PeterBurgess said:
Even taking away the ad for Superflow, it makes interesting reading. I must admit though, I prefer the inertia testing as I cannot help but feel cars are either accelerating or cruising but not holding exact rpm at wide open throttle. Seems to work for us as we have been able to improve acceleration out of bends since we have had the inertia rollers. We use the pau to hold full load to make sure we are not detonating after we have done the inertia tuning.
Peter
non inertia testing does not mean only static test. ive never seen anyone tune on a chassis dyno WOT by holding at fixed rpm this is usually done at low rpm and medium load and below only. they usually use a linear ramp rate for WOT so the engine rpm varies linearly with time as opposed to inertia where the acceleration is proportional to the torque outputPeter
Our old water brake Clayton was manual load and I had a load/unload button, so we had to do static loading at each desired rpm then move to the next rpm for sampling, then do a high rpm to low rpm run by holding the load button to get an idea of the power curve. If you are doing step tests on a controlled integrated sampling rolling road then surely you are doing static load but for very short time, then unload and move to next rpm load site? To my way of thinking, if the load is held for even a fraction of a second before moving on that is a static test. So the actual test is not and cannot be smooth compared to an inertia run. I also would be interested in afr comparisons between a small rpm increment per second test and an inertia run. From my perspective I feel the inertia runs give us afrs more akin to data logged on the track and the static load ( as I call it) runs tend to end up richer when used in anger on a track. Another problem I have seen with sampling at a high rpm/sec pau run is turbos spool up too slow. We tend to just add a % base load to our PAU to spool up turbos and make em work. We also use a % pau base load for N/As around and above 400 bhp.
I have been dynoing cars on my own rolling roads for 29 years and changed to a modern Dynocom inertia/pau rolling road from my old Clayton waterbrake in 2010. The biggest difference I have found in tuning is being able to look very closely at effects of timing and fuelling especially at less than peak power points. This lets us improve the power out of bends on the track/road. Another good thing is the speed of data acquisition. We can see the effects of the year on year increase in % ethanol on our old non self correcting carbie cars. For the last few years of using the Clayton we used an Innovate afr monitor as our old CO meters were not quick enough responding.
I am looking forwards to using the Superflow engine dyno but feel I will end up with not a lot of time to experiment using a donkey engine with effects of load/s runs etc etc. We are beginning to get a few folk wanting to use the facilities for bedding in some big bhp engines so, as I cannot magic up more Peter hands or Peter time I will have to do the paying work first to cover operating costs. I am still awaiting industry standard engine test technique info from some of our more learned PH members who work in the Automotive Manufacturing Industry rather than myself who works more in the amateur tuning industry. The Superflow manual has a lot of info but that is not same as manufacturers methods methinks.
Peter
I have been dynoing cars on my own rolling roads for 29 years and changed to a modern Dynocom inertia/pau rolling road from my old Clayton waterbrake in 2010. The biggest difference I have found in tuning is being able to look very closely at effects of timing and fuelling especially at less than peak power points. This lets us improve the power out of bends on the track/road. Another good thing is the speed of data acquisition. We can see the effects of the year on year increase in % ethanol on our old non self correcting carbie cars. For the last few years of using the Clayton we used an Innovate afr monitor as our old CO meters were not quick enough responding.
I am looking forwards to using the Superflow engine dyno but feel I will end up with not a lot of time to experiment using a donkey engine with effects of load/s runs etc etc. We are beginning to get a few folk wanting to use the facilities for bedding in some big bhp engines so, as I cannot magic up more Peter hands or Peter time I will have to do the paying work first to cover operating costs. I am still awaiting industry standard engine test technique info from some of our more learned PH members who work in the Automotive Manufacturing Industry rather than myself who works more in the amateur tuning industry. The Superflow manual has a lot of info but that is not same as manufacturers methods methinks.
Peter
History is a b
h.
The problem with any method of extrapolating flywheel power from power measured at the wheels/hubs is that you paint yourself into a corner.
If my car makes 200 hp at the rollers, and the dyno (in 1980) says that is 250 at the flywheel, 35 years on, I expect 200 WHP to still read 250 at the flywheel on that brand dyno, even a 2016 model.
We do a lot of comparisons between chassis, engine and hub dynos, but I can't change the existing corrections, or everyone would be saying "why is the flywheel power different on the new model?". Once you set a "standard", it hangs around your neck forever
, so I have some sympathy for Dynojet here.
Having said that, IMO dynojets read high. We get asked "how do I make it read the same as a Dynojet" on a semi-regular basis.
Unfortunately there are people out there who go "dyno shopping" looking for the workshop that can give them a printout with the biggest HP number for bragging rights. These people should be shot and mulched up as fertiliser.
The companies that provide dyno charts showing "horsepower" without specifying whether it is power measured at the wheels or estimated at the flywheel would also go in the mulcher if I was in charge, along with their customers who don't know whether the chart is tyre or flywheel power, or don't know the difference.
As you can probably tell, sales is not my calling.
h.The problem with any method of extrapolating flywheel power from power measured at the wheels/hubs is that you paint yourself into a corner.
If my car makes 200 hp at the rollers, and the dyno (in 1980) says that is 250 at the flywheel, 35 years on, I expect 200 WHP to still read 250 at the flywheel on that brand dyno, even a 2016 model.
We do a lot of comparisons between chassis, engine and hub dynos, but I can't change the existing corrections, or everyone would be saying "why is the flywheel power different on the new model?". Once you set a "standard", it hangs around your neck forever
, so I have some sympathy for Dynojet here.Having said that, IMO dynojets read high. We get asked "how do I make it read the same as a Dynojet" on a semi-regular basis.
Unfortunately there are people out there who go "dyno shopping" looking for the workshop that can give them a printout with the biggest HP number for bragging rights. These people should be shot and mulched up as fertiliser.
The companies that provide dyno charts showing "horsepower" without specifying whether it is power measured at the wheels or estimated at the flywheel would also go in the mulcher if I was in charge, along with their customers who don't know whether the chart is tyre or flywheel power, or don't know the difference.
As you can probably tell, sales is not my calling.
I cannot agree with you more. We are happiest quoting wheel power. We do do the coast down losses and tell them it is a ball park flywheel figure but more than anything we are ensuring losses are the same for same type of vehicle so no unexpected losses. When we tell folk what sort of power to expect we say 'on our rolling road' and equate it with a standard car on our rolling road for increases. It can get worse with folk shopping around for race engines as big numbers tend to sell well. We get folk who use Peter Baldwins rollers and are worried that we quote maybe 50 bhp less at the wheels. Petes dyno reads what it reads and so does ours. The comparisons, as you say, are fruitless and impossible. Repeatability and operator skills are all that is needed to make it a good dyno. When we updated our MGB tuning book we added loads and loads of new info and graphs derived from the Dynocom rolling road. We kept all the Clayton figures in the book and explained they could not be compared but each held true like for like testing.
Peter
Peter
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
I'm not sure what the point of "estimating" gross engine power is??
What matters is Brake Power at the flywheel. Accurate calculation of engine friction from cylinder pressure or via various other means (such as motoring tests) allows us to MEASURE engine frictional and parasitic losses, but to "estimate" them?? Why?
What matters is Brake Power at the flywheel. Accurate calculation of engine friction from cylinder pressure or via various other means (such as motoring tests) allows us to MEASURE engine frictional and parasitic losses, but to "estimate" them?? Why?
Max_Torque said:
I'm not sure what the point of "estimating" gross engine power is??
What matters is Brake Power at the flywheel. Accurate calculation of engine friction from cylinder pressure or via various other means (such as motoring tests) allows us to MEASURE engine frictional and parasitic losses, but to "estimate" them?? Why?
I am not sure if you are referring to my earlier post or not.What matters is Brake Power at the flywheel. Accurate calculation of engine friction from cylinder pressure or via various other means (such as motoring tests) allows us to MEASURE engine frictional and parasitic losses, but to "estimate" them?? Why?
I was referring to estimating flywheel power based on measured power at the rollers.
The gross engine power is used as part of the atmospheric correction calculation.
I have some questions about atmospheric correction and turbo engines : if the ecu is controlling MAP via regulating turbo boost, the power output should not be affected by barometric pressure, or at least to a lesser degree than a NA engine.
The most important thing about atmospheric correction a la SAE J95 is that they set a maximum allowable atmos. correction of 10%.
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