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Thread: Rolling road figures - believable or not?

  
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    Rolling road figures - believable or not?

    Loads of us here go on about the rolling road figures for our cars, then we get the usual 'Oh they're not accurate, there's no way you're getting that much from that engine!'.

    What is classed as an accurate rolling road? If people have had their cars RR'd on a few different roads, and they all come back with similar figures, then is this not good enough as a test?

    If a group of cars are tested and, where they have been done elsewhere before, have similar figures to previously, then again is this not acceptable to then trust the figures given to cars which have never been tested before?

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    Quote Originally Posted by nry View Post
    If a group of cars are tested and, where they have been done elsewhere before, have similar figures to previously, then again is this not acceptable to then trust the figures given to cars which have never been tested before?
    Read that 6 times and still no clearer to me... epic sentence!

    IMO the only really way to tell is by having a large group of people that have used several different rollers and work off their general feeling.

    That is why we decided JDM rollers are running high!

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    Quote Originally Posted by nry View Post
    Loads of us here go on about the rolling road figures for our cars, then we get the usual 'Oh they're not accurate, there's no way you're getting that much from that engine!'.

    What is classed as an accurate rolling road? If people have had their cars RR'd on a few different roads, and they all come back with similar figures, then is this not good enough as a test?

    If a group of cars are tested and, where they have been done elsewhere before, have similar figures to previously, then again is this not acceptable to then trust the figures given to cars which have never been tested before?
    Because some people claim 10+bhp with bog standard cars.

    I know turbocharged engines can fluctuate in power and some can be 195 or 205 (book figure 200) but this is due to the nature of a turbocharged engine, air temps etc play a big part.

    N/A engines usually have less scope for power fluctuations. They don't have a fan forcing air into the engine so lack of air doesn't cause such a big drop in bhp.

    Also, people will take their car to one RR and get 240bhp and then go elsewhere and get 270bhp. Which is correct? Or should they just say it's 255bhp because it's the middle number?

    Should a cars bhp be measured on the coldest day of the year or the hottest? The hottest means it'll produce less power and the coldest means it'll produce more. (Going back to my first point, more power fluctuation with the turbo and less with N/A).

    People will always measure their cars bhp on the coldest day possible, but is this a real world result for the cars performance as we don't have -3 degrees C all year around, so that extra 2bhp or whatever might not be there in Spring, Summer or Autumn.

    I've had this discussion with numerous people before and tbh people become stubborn and won't look at it objectively, especially if they have got an RR figure alot higher than normal. (Even more so if it's a standard car).

    As for mods, put a full exhaust system (for example) on a turbocharged car and you'll see a greater bhp increase than on an N/A car but it's not something that will set the world on fire, especially if the car has no other mods.


    PS: I remember visiting M-Sport and the guy said he would never believe a regular rolling road. When they test their engines for performance they use an air tight room with loads of fancy expensive equipment, not two rollers and a PC. (Yes I know there's more to it than that).
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    Quote Originally Posted by npd View Post
    Read that 6 times and still no clearer to me... epic sentence!

    IMO the only really way to tell is by having a large group of people that have used several different rollers and work off their general feeling.

    That is why we decided JDM rollers are running high!
    I meant what you said, but you said it better

    For the NA cars at JDM, so far as I can tell all figures were almost identical to those people had from elsewhere.

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    Quote Originally Posted by nry View Post
    I meant what you said, but you said it better

    For the NA cars at JDM, so far as I can tell all figures were almost identical to those people had from elsewhere.
    I seem to recall someone telling me of an Astra G Turbo (Standard) getting 240bhp @ JDM.
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    Hence my comment about NA cars - I believe the more powerful cars had issues with slipping on the rollers due to lack of grip which skewed some results.

    I go back to Ffoeg's 2.2 which pulled in almost bang on the 180bhp mark, only 1bhp difference to previous results elsewhere and the variations in the Z16XE's tested showed acceptable differences depending on the mods they had at the time.

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    IMO too many people get caught up in hanging the **** out with rolling road results.

    The problem with them as there are that many variables involved add to the fact that many rolling roads are not maintained properly, and also a rolling road is only as good as its operator.

    IMO they should only really be used as a guide, and as a tool to ensure the car is running as it should be. Hence why Ive only ever used Star Performance for rolling roading my car (exception to that would be when I had my Evo mapped at Wallace Performance, produced 349bhp on their rollers, next day it was at a rolling road day at Dastek (both use the same rolling road setup) and the car made 350bhp).

    An example of how easy it is to fudge figures on a rolling road is an incident I had at Star back in 2002. When I got my Vectra SRi 2.6 I rolling roaded it after every mod to see what actual difference it made, during one of these runs the car had previously ran 202bhp, I changed the airbox setup and took it back to see the difference, it came out with 266bhp, not bad for an airbox mod, the problem had came where Jim had inadvertently put the heat prob onto the exhaust manifold hence when the computer made its adjustments it read the outside temp as well over 100degrees which is why it came back with that figure, a quick adjustment later and it came back with 204bhp. A good example imo as to how a rolling road can be manipulated.

    The other factor is that a rolling road flywheel figure is just a calculation, its not really an exact figure (hence why the Evo guys all quote their bhp at the wheels rather than flywheel, although in Vauxhall land we seem determined to quote flywheel figures to make it look more impressive).

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    Quote Originally Posted by Turbo_Scott View Post
    I seem to recall someone telling me of an Astra G Turbo (Standard) getting 240bhp @ JDM.
    Bonjour!

    Hence my comment about NA cars - I believe the more powerful cars had issues with slipping on the rollers due to lack of grip which skewed some results.

    I go back to Ffoeg's 2.2 which pulled in almost bang on the 180bhp mark, only 1bhp difference to previous results elsewhere and the variations in the Z16XE's tested showed acceptable differences depending on the mods they had at the time.
    I got the impression from Mr F that the ffoeg-mobile was running high too.

    Mine did not slip at all. That was only Kev's at our last visit.

    For me the proof is in the pudding... when he 'tweaked' a setting for a laugh and Marti ran 170bhp!!


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    Quote Originally Posted by npd View Post
    Bonjour!
    Ahhhh oui!


    Back to the topic , If you don't have much bhp then you can always use the old "It's how you drive it anyways" excuse.
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    Interesting thread and read for me!! some good and valid points touched upon by both Scott and Dave. Unfortunately this is and will be the nature of tuning.. There will always be discrepancies in the rr figures produced at different rr centres. As mentioned there are loads of factors that influence this.. Does anyone truly know the exact figures that their car is running??!... As Dave has said rr figures should be taken as a guideline rather than as a fact. I have known people on the AOC quote higher figures everytime they talk about their car, without any additional modifications everytime their car is rr. The most important thing is how your car drives..
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