Hopefully a stupid question
Discussion
When checking the power, torque and fueling of a car on a rolling road, should the car be "plugged" into the rolling road equipment.
The reason I ask is that, when I took mine to a rolling road in the summer, there were no wires connected to anything under the bonnet, or similary to anything inside the car? How on earth do they manage to produce the graphs with no obvious outputs from the car other than the speed of the back wheels and maybe a probe up the exhaust.
I assume that the rolling road results they produced were genuine, but I am at a loss to understand how they were produced.
Thanks
Andy
The reason I ask is that, when I took mine to a rolling road in the summer, there were no wires connected to anything under the bonnet, or similary to anything inside the car? How on earth do they manage to produce the graphs with no obvious outputs from the car other than the speed of the back wheels and maybe a probe up the exhaust.
I assume that the rolling road results they produced were genuine, but I am at a loss to understand how they were produced.
Thanks
Andy
I think it's somehting to do with the way your rear wheels turn the rollers and then slow down again which measures the power at the rear wheels and then converts that into flywheel BHP & torque. If you wanted to tune the mapping you would indeed need to be "plugged in" but not for just a BHP/torque measurement. Hopefully someone like GreenV8S or Barcychoc will be along shortly with a proper explanation.
You need an engine speed input in order to scale the power curve and in order to calculate the torque curve from it. You may be able to get a rough idea of the revs by looking at the rev counter during the run and manually set the peak RPM and work back from there, but it sounds a very naff way to do it; these rev counters aren't particularly accurate. Or you might assume what the gearing was in the gear you were using and estimate the engine speed from the roller speed. Also rather inaccurate since it doesn't account for tyre slip, but if you aren't bothered about that sort of thing ...
I think that to do the job properly, you need to connect at least an engine speed sensor.
I think that to do the job properly, you need to connect at least an engine speed sensor.
I don't pretend to be any kind of expert but I guess all measurements would be done in 4th gear - as on most cars this is straight through the gearbox at a ratio of 1:1 (and as a result there is least strain on the transmission in 4th) so you've then only got to say hold the car at 3000 revs and you can get a speed /rpm reading that again I guess would then be typed into the rolling road or a button pressed or something to register that speed.
Once you've got the factor figure between engine speed and road speed I don't see you need much else.
All guesses totally off the top of my head, anyone feel free to shoot me down if this is rubbish.
Once you've got the factor figure between engine speed and road speed I don't see you need much else.
All guesses totally off the top of my head, anyone feel free to shoot me down if this is rubbish.
techbotics said:
In 4th the rollers can measure engine and road speed.
I don't believe they can measure the engine speed.They can measure the roller speed. The tyre speed can be estimated from that - you might ignore slip/creep and assume they're the same if you aren't too fussy.
Somebody who knows the diff and gearbox gearing in the gear being used can calculate the engine speed from the tyre speed. But unless you know what the gearing is - you can't know the engine revs from the roller speed. I've been shown rolling road charts where the rolling road produced some completely weird power and torque curves that bore no relation to the engine's actual performance, because the operator guessed the gearing wrong.
GreenV8S said:
I don't believe they can measure the engine speed.
They can measure the roller speed. The tyre speed can be estimated from that - you might ignore slip/creep and assume they're the same if you aren't too fussy.
Somebody who knows the diff and gearbox gearing in the gear being used can calculate the engine speed from the tyre speed. But unless you know what the gearing is - you can't know the engine revs from the roller speed. I've been shown rolling road charts where the rolling road produced some completely weird power and torque curves that bore no relation to the engine's actual performance, because the operator guessed the gearing wrong.
actually I think you are right when I had the cosworth and had it dyno the did select my car type prior to the run. this I assume would load the appropriate params to enable the calculation. They can measure the roller speed. The tyre speed can be estimated from that - you might ignore slip/creep and assume they're the same if you aren't too fussy.
Somebody who knows the diff and gearbox gearing in the gear being used can calculate the engine speed from the tyre speed. But unless you know what the gearing is - you can't know the engine revs from the roller speed. I've been shown rolling road charts where the rolling road produced some completely weird power and torque curves that bore no relation to the engine's actual performance, because the operator guessed the gearing wrong.
Wonder if the TVR is in the database it may well be.
D S3
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