ROLLING ROAD V LAPTOP
13 February 2009, 07:38 AM
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dont think you will ever get a right answer on this one
i had mine done on the road, but going rollers in 2 weeks so will see if the figures are the same..
i would of thought that the more acurate reading would be on the rollers but then you could say that you dont drive your car on the rollers everyday so on the road could be a more true to life reading
could ask JGM as i know he does abit of both (well so i was told)
i had mine done on the road, but going rollers in 2 weeks so will see if the figures are the same..
i would of thought that the more acurate reading would be on the rollers but then you could say that you dont drive your car on the rollers everyday so on the road could be a more true to life reading
could ask JGM as i know he does abit of both (well so i was told)
Last edited by phil739; 13 February 2009 at 07:41 AM.
13 February 2009, 07:43 AM
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The only accurate figure youll ever get will be from an engine dynometer.
Tyre pressure, gearbox oil temperature and a number of other factors can make the wheels figure from a chassis dyno inaccurate and the 'at the flywheel' figure is innacurate at best and damned fanciful at worst. To anyone whos about to tell me about the 'coastdown': youll get a different figure in 3rd; 4th and 5th, which makes a nonsense of it: doesnt it?
Tyre pressure, gearbox oil temperature and a number of other factors can make the wheels figure from a chassis dyno inaccurate and the 'at the flywheel' figure is innacurate at best and damned fanciful at worst. To anyone whos about to tell me about the 'coastdown': youll get a different figure in 3rd; 4th and 5th, which makes a nonsense of it: doesnt it?
13 February 2009, 07:54 AM
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Originally Posted by dynamix
You get a different figure for losses but you also get a different figure for wheel horsepower. Added together they come to roughly the same.
Originally Posted by dynamix
Whether you use road dyno or chassis dyno - they are a tuning tool.
13 February 2009, 08:02 AM
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Its as accurate as the operater - who decides the weight of the car and its Cd for the road dyno? what procedures are done for the coastdown on the rollers?
At the end of the day its consistancy of calculation that matters, so that different runs can be compared with some degree of confidence.
At the end of the day its consistancy of calculation that matters, so that different runs can be compared with some degree of confidence.
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13 February 2009, 09:07 AM
#10
Although the supplied graph may be titled "wheel power", many Ecutek tuners are adding a transmission loss to the normal wheel power graph, but the "wheel power" entry can't be altered.
If unsure then ask your tuner if the Ecutek road dyno graph is wheel or estimated flywheel power.
13 February 2009, 09:16 AM
#11
The only accurate figure youll ever get will be from an engine dynometer.
Tyre pressure, gearbox oil temperature and a number of other factors can make the wheels figure from a chassis dyno inaccurate and the 'at the flywheel' figure is innacurate at best and damned fanciful at worst. To anyone whos about to tell me about the 'coastdown': youll get a different figure in 3rd; 4th and 5th, which makes a nonsense of it: doesnt it?
Tyre pressure, gearbox oil temperature and a number of other factors can make the wheels figure from a chassis dyno inaccurate and the 'at the flywheel' figure is innacurate at best and damned fanciful at worst. To anyone whos about to tell me about the 'coastdown': youll get a different figure in 3rd; 4th and 5th, which makes a nonsense of it: doesnt it?
You MUST get different results in different gears, because POWER has an element of speed in it. And less that 10% of the total drivetrain losses are related to friction.
13 February 2009, 09:38 AM
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Would you like me to spend my working day trawling through the internet finding empirical evidence to prove an accepted fact? Perhaps you should reference one credible article which shows me that 'at the flywheel' chassis dynometer figures are anything more than a 'best guess'.
13 February 2009, 09:50 AM
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my cars a my00 by the way
so if the clinic measure from the wheels will the figure be a big difference to the one done on the road by JGM??
13 February 2009, 09:58 AM
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I'm with GC8 on the fact that the only reliable way of measuring flywheel power is to measure it directly, get rid of the transmission and wheels, to do anything else is simply an estimate, perhaps a reasonably accurate one, but nevertheless an estimate.
I'm with Paul on the fact that losses will vary with speed and I'm surprised that astute as GC8 seems to be that little bit seems to have eluded him. I invite him to fit a sufficiently tall gearbox to a 1 litre Micra and then try to get its wheels to turn at 400MPH on a rolling road. If the losses were not speed related then that should be "trivial", if they can turn at 30MPH and the losses don't increase then all that is needed is a tall gear to turn them at 400MPH. The reality is that the Micra's engine cannot produce sufficient power to overcome the transmission loss at that speed.
There is also interesting empirical data that suggests that the losses are not as measured by coastdown, but then one has to ask, is the coastdown measured directly or is it corrected for the additional losses experienced on load. It's a bit of a minefield, and we've covered this topic to death already, so let's just say that a dyno is a useful tuning tool that can show you if you're making gains or not by ratiometric measurements rather than absolute, and it can also be useful to compare vehicles, again because it is ratiometric, but any absolute figures that cannot be measured directly should be treated as an estimate.
Cheers,
Pat.
I'm with Paul on the fact that losses will vary with speed and I'm surprised that astute as GC8 seems to be that little bit seems to have eluded him. I invite him to fit a sufficiently tall gearbox to a 1 litre Micra and then try to get its wheels to turn at 400MPH on a rolling road. If the losses were not speed related then that should be "trivial", if they can turn at 30MPH and the losses don't increase then all that is needed is a tall gear to turn them at 400MPH. The reality is that the Micra's engine cannot produce sufficient power to overcome the transmission loss at that speed.
There is also interesting empirical data that suggests that the losses are not as measured by coastdown, but then one has to ask, is the coastdown measured directly or is it corrected for the additional losses experienced on load. It's a bit of a minefield, and we've covered this topic to death already, so let's just say that a dyno is a useful tuning tool that can show you if you're making gains or not by ratiometric measurements rather than absolute, and it can also be useful to compare vehicles, again because it is ratiometric, but any absolute figures that cannot be measured directly should be treated as an estimate.
Cheers,
Pat.
13 February 2009, 11:09 AM
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I'm with GC8 on the fact that the only reliable way of measuring flywheel power is to measure it directly, get rid of the transmission and wheels, to do anything else is simply an estimate, perhaps a reasonably accurate one, but nevertheless an estimate.
I'm with Paul on the fact that losses will vary with speed and I'm surprised that astute as GC8 seems to be that little bit seems to have eluded him. I invite him to fit a sufficiently tall gearbox to a 1 litre Micra and then try to get its wheels to turn at 400MPH on a rolling road. If the losses were not speed related then that should be "trivial", if they can turn at 30MPH and the losses don't increase then all that is needed is a tall gear to turn them at 400MPH. The reality is that the Micra's engine cannot produce sufficient power to overcome the transmission loss at that speed.
There is also interesting empirical data that suggests that the losses are not as measured by coastdown, but then one has to ask, is the coastdown measured directly or is it corrected for the additional losses experienced on load. It's a bit of a minefield, and we've covered this topic to death already, so let's just say that a dyno is a useful tuning tool that can show you if you're making gains or not by ratiometric measurements rather than absolute, and it can also be useful to compare vehicles, again because it is ratiometric, but any absolute figures that cannot be measured directly should be treated as an estimate.
Cheers,
Pat.
I'm with Paul on the fact that losses will vary with speed and I'm surprised that astute as GC8 seems to be that little bit seems to have eluded him. I invite him to fit a sufficiently tall gearbox to a 1 litre Micra and then try to get its wheels to turn at 400MPH on a rolling road. If the losses were not speed related then that should be "trivial", if they can turn at 30MPH and the losses don't increase then all that is needed is a tall gear to turn them at 400MPH. The reality is that the Micra's engine cannot produce sufficient power to overcome the transmission loss at that speed.
There is also interesting empirical data that suggests that the losses are not as measured by coastdown, but then one has to ask, is the coastdown measured directly or is it corrected for the additional losses experienced on load. It's a bit of a minefield, and we've covered this topic to death already, so let's just say that a dyno is a useful tuning tool that can show you if you're making gains or not by ratiometric measurements rather than absolute, and it can also be useful to compare vehicles, again because it is ratiometric, but any absolute figures that cannot be measured directly should be treated as an estimate.
Cheers,
Pat.
If anyones bored and would like some light reading, Ive written a magazine article on this topic that beginners should be able to understand that I'm happy to link to.
13 February 2009, 01:21 PM
#20
someone opened a can of worms here .... 
for what its worth when Bob mapped my car, his laptop readout came out at 343/343, a few months later on a rolling road it came out at 347/343 .....
I was expecting a bit less, especially torque, whether it was just those rollers I dont know, will find out when it goes on the rollers at powerstation in a few weeks time.
just my contribution
for what its worth when Bob mapped my car, his laptop readout came out at 343/343, a few months later on a rolling road it came out at 347/343 .....
I was expecting a bit less, especially torque, whether it was just those rollers I dont know, will find out when it goes on the rollers at powerstation in a few weeks time.
just my contribution
13 February 2009, 01:26 PM
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someone opened a can of worms here ....
for what its worth when Bob mapped my car, his laptop readout came out at 343/343, a few months later on a rolling road it came out at 347/343 .....
I was expecting a bit less, especially torque, whether it was just those rollers I dont know, will find out when it goes on the rollers at powerstation in a few weeks time.
just my contribution
for what its worth when Bob mapped my car, his laptop readout came out at 343/343, a few months later on a rolling road it came out at 347/343 .....
I was expecting a bit less, especially torque, whether it was just those rollers I dont know, will find out when it goes on the rollers at powerstation in a few weeks time.
just my contribution
13 February 2009, 06:23 PM
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The reason i asked this question to start was that my car 2008 sti lost alot of performance just like flicking a switch. the dealership had the car back and said all was fine they all run like this.to prove this incorrect the car went on the rollers on tuesday result 261bhp 272llb torque,took the car back tuesday afternoon with the print off.wednesday told me that subaru rejected the power run saying this does not give an acurate reading and that they test them using a laptop.telephone call this morning from dealership fault on one cylinder which i assume is ringland failure so are replacing engine or rebuilding old unit will have to wait and see.
13 February 2009, 06:44 PM
#24
Would you like me to spend my working day trawling through the internet finding empirical evidence to prove an accepted fact? Perhaps you should reference one credible article which shows me that 'at the flywheel' chassis dynometer figures are anything more than a 'best guess'.
14 February 2009, 10:50 AM
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I'm interested to know why you say that as I have pulled apart plenty over my 20+ years as a vehicle technician / tuner but don't know which part of the article you are commenting on specifically so will refrain from telling you what you should or shouldn't be doing as I don't know you, your experience or your capabilities.
Instead I will ask you to clarify, but please bear in mind that my articles are written specifically with the layman in mind and specifically ignore some technical issue on purpose so as not to lose the reader.
Last edited by Evolution Stu; 14 February 2009 at 10:57 AM.
14 February 2009, 11:12 AM
#28
By interesting, I didn't mean exclusively incorrect, but...
I don't know of any cars (any that we would be interested in measuring the power of) that use a direct drive for 4th gear, even 1:1 ratio 4th gears will use a pair of gears to transmit the drive to the output shaft, and very importantly, reverse the direction of the drive. Using a 1:1 gear, or a 1.1:1 gear will have no influence on the accuracy of the measurement, the efficiency of the gears will be largely the same, around the 98% mark, so any changes to the losses introduced by the gear itself will result in very small changes to the accuracy of the measurement. My personal experience is that differences in out put between different gears are low when estimated back to the flywheel by coastdown measurement, and that it is more appropriate to run any given car in whatever gear provides the best compromise between engine loading, run time, tyre problems and peak speed on the dyno. Running a car in a lower gear will yield lower losses, and if you can lower the losses to a minimum, and estimate involving them is going to be more accurate.
As you point out, windage [and viscous] losses are a big factor, and massively dominate proceedings, along with losses from the hypoid gears, but they again are relatively low in the grand scheme of things.
I didn't have much time when I last sat down. But I have to say it's the first time I've seen an article with a very common sense approach to the overall nature of dynos. I would disagree with some statements (as above), all it really lacks is some comparative numbers for the tech heads, any dyno comparisons on the horizon? That would be very interesting, engine dyno, hub dyno, coastdown chassis dyno, guestimate chassis dyno.
I don't know of any cars (any that we would be interested in measuring the power of) that use a direct drive for 4th gear, even 1:1 ratio 4th gears will use a pair of gears to transmit the drive to the output shaft, and very importantly, reverse the direction of the drive. Using a 1:1 gear, or a 1.1:1 gear will have no influence on the accuracy of the measurement, the efficiency of the gears will be largely the same, around the 98% mark, so any changes to the losses introduced by the gear itself will result in very small changes to the accuracy of the measurement. My personal experience is that differences in out put between different gears are low when estimated back to the flywheel by coastdown measurement, and that it is more appropriate to run any given car in whatever gear provides the best compromise between engine loading, run time, tyre problems and peak speed on the dyno. Running a car in a lower gear will yield lower losses, and if you can lower the losses to a minimum, and estimate involving them is going to be more accurate.
As you point out, windage [and viscous] losses are a big factor, and massively dominate proceedings, along with losses from the hypoid gears, but they again are relatively low in the grand scheme of things.
I didn't have much time when I last sat down. But I have to say it's the first time I've seen an article with a very common sense approach to the overall nature of dynos. I would disagree with some statements (as above), all it really lacks is some comparative numbers for the tech heads, any dyno comparisons on the horizon? That would be very interesting, engine dyno, hub dyno, coastdown chassis dyno, guestimate chassis dyno.
Last edited by Pavlo; 14 February 2009 at 01:17 PM.
14 February 2009, 11:40 AM
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I (as a layman) found it very informative, and intend reading all of your tec articles..
Personally, I can't get enough of stuff like that..
Good work Stu, you should make them a sticky on here or maybe a good basis for a new How to tec section in Technical..?
Personally, I can't get enough of stuff like that..
Good work Stu, you should make them a sticky on here or maybe a good basis for a new How to tec section in Technical..?
14 February 2009, 12:46 PM
#30
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I don't know of any cars (any that we would be interested in measuring the power of) that use a direct drive for 4th gear, even 1:1 ratio 4th gears will use a pair of gears to transmit the drive to the output shaft, and very importantly, reverse the direction of the drive. Using a 1:1 gear, or a 1.1:1 gear will have no influence on the accuracy of the measurement, the efficiency of the gears will be largely the same, around the 98% mark, so any changes to the losses introduced by the gear itself will result in very small changes to the accuracy of the measurement. My personal experience is that differences in out put between different gears are low when estimated back to the flywheel by coastdown measurement, and that it is more appropriate to run any given car in whatever gear provides the best compromise between engine loading, run time, tyre problems and peak speed on the dyno. Running a car in a lower gear will yield lower losses, and if you can lower the losses to a minimum, and estimate involving them is going to be more accurate.
As you point out, windage [and viscous] losses are a big factor, and massively dominate proceedings, along with losses from the hypoid gears, but they again are relatively low in the grand scheme of things.
As you point out, windage [and viscous] losses are a big factor, and massively dominate proceedings, along with losses from the hypoid gears, but they again are relatively low in the grand scheme of things.
This is a classic case of over simplification actually leading to readers with more technical knowledge thinking you actually mean something else. My fault entirely.
What I was trying (Obviously not hard enough) to explain was that when we select a gear ratio of 1:1 we are trying to intentionally cancel out the multiplication effect of the gearbox and thus lose the associated transmission losses in doing so. I made an **** of that though it seems.
I didn't have much time when I last sat down. But I have to say it's the first time I've seen an article with a very common sense approach to the overall nature of dynos. I would disagree with some statements (as above), all it really lacks is some comparative numbers for the tech heads, any dyno comparisons on the horizon? That would be very interesting, engine dyno, hub dyno, coastdown chassis dyno, guestimate chassis dyno.
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