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Rolling Roads accuracy ?

StephaneS Oct 6, 2004

  1. StephaneS

    StephaneS Member

    I am trying to get to the bottom of what are the power and torque figures we get from different companies as I’ve seen so many different and odd figures (wishful thinking I know /ubbthreads/images/graemlins/blush.gif).
    But I looked at some very interesting posts (Haldex one with Ulf’s letter was very informative) and checked the AMD explanation of torque, bhp and figures on rollers from their website.
    Well I have never been in a RR session so I am kind of stuck so am looking for some answers of people in the know :

    First of all what do RR benches measure and how?
    My guess:
    It measures power in kW on each individual wheel and/or it measures the torque in Nm on each individual wheel
    You continuously measure the rpm of the rolling cylinders and with the time period of measurement samples you can calculate the acceleration. Now knowing the inertia of these cylinders and the (calibrated?) friction loss of their bearings you get the power.
    If that guess is correct, apart from sensors themselves, inaccuracy would come mainly from slip between tyres and cylinders and from calibration.
    Then you would get a figure for each wheel so what do you do after that? sum it up? and how do you account for the haldex clutch especially since there must be some slippage (assuming ESP off)?
    Then from this data, that I will suppose to be wheel horse power, I understand you have to use the 2 famous correction factors that will make all the differences…
    One being due to temperature and pressure compared to DIN standard at 20°C and ??mbar. OK that is down to tuners’ professionalism (honesty?)
    Then there is the big blur about the drive train correction to get the flywheel bhp? Can anyone explain me as I cant figure out how you can know/measure this?

    Finally on the AMD website, they mention these figures about NA engine out from production: average between 0.9 and 1.1 ft-lbs per cubic inch of engine size. I checked for mine using VF engineering RR results at the wheels, and it is bang on : 1.0045 ft-lbs per cubic inch.
    (Btw it would be interesting if anyone had the same figures for turbo cars)
    Using the same ratio for tuned engines that would mean that my car would get between 214.8 and 253ft-lbs at the wheels if highly tuned. Sounds really good to me so can anyone explain me what that “highly tuned” expression would mean for my car?
    Second step: what can you do to get your engine to rev higher?

  2. StephaneS

    StephaneS Member

    Did I post on the wrong forum, or just that noone knows/cares?

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