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Thread: BHP and gears

  
  1. #1
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    BHP and gears

    ok i have sod all idea where to put this because its not any specific car related, nor mechanical related really, so sod it.. chit chat seems the right option.. ( sorry if its not tho )


    Do it matter what gear you use when running your car on the rollers?

    im asking because im looking over my old RR printouts from 2008 / 2009 and trying to figure out a few things, like how i managed to loose 30 BHP after fitting a sports cat and full exhaust system ...hmmmmmmmmmmmmmm

    I do know on my last RR i had a issue with my AFM and a dodgy MAP sensor, and i also didint remove the TC tuse, just turned it off... just trying to eliminate things etc....

    any ideas?
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    it will be down to not removing the fuse mate, turning it off on the buton doesnt fully disable it. it is still active and will sense the rear wheels arnt turning so will still limit power.

    my gsi was rollered before i owned it, with the tc button just turnt off and it made 114bhp, a minute later the fuse was removed and it made std power, as it should have as it had no mods bar a cat back

    4th and 5th are generaly the best gears rolling road it in although the dyno dynamics rolling roads are done in 3rd.
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    4th seems the usual choice, though I think BHP is the same in all gears. Unless of course the car is specifically mapped to reduce boost/power in a certain gear. I think MK4's have reduced boost in first.

    Guess 4th is used as the gear is long enough to give an accurate reading + less chance of wheel spin compared to 3rd.

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    1st and second are limited on regals maps as far as im aware, they always do mine in 5th.

    5th will give a good reading from about 30mph to max speed allowing the full rev range to be read correctly.
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    all the RR I've been to tend to use 4th gear for the run.
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    It should be done in whichever gear is nearest to 1:1 ratio otherwise incorrect flywheel figures will be obtained, gearboxes are 'torque multipliers'.
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    mine seem to be 4th gear..

    the fuse im not 100% convinced with tho m8..

    A standard GSi ran with TC turnd off and hit bang on, mine ran and was hitting 230 bhp..
    thing is im no sure if its been down to stem seals that wer going ( and still are ), AFM that was temprimental and MAP sensor that worked when i wants to...

    sinve my RR run in 2008 where i hit 258.6 bhp i have added a sports cat and full exhaust and lost 28bhp
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    most astra turbo's loose alot of power by not having the fuse removed, quite a well known thing.

    a dodgy afm shouldnt loose 30bhp, it will just mess up the fueling at high revs,
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    Quote Originally Posted by afcbadam View Post
    most astra turbo's loose alot of power by not having the fuse removed, quite a well known thing.
    yup i know.. im the very one that says remove it BUT at this day it wasnbt removed on 6 cars and on 4 o them they wer bang on for what they thought they had

    strange one this..

    i cant find the sheet from taht run tho... i wonderd if it had been run in 3rd gear as the SRi was at the weekend...

    but didnt think the gear would make a diff really tho
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