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Thread: Horsepower math acts weird

  1. #1
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    Horsepower math acts weird

    I have been logging delivered torque a lot and at least in these cars (mostly gen3 LS engines) it has been accurate enough to calculate delivered horsepower. This has been proved in dyno many times.

    Now I realized there's math option in scanner and I made my math there:
    (([50108.120]*[50070.56])/9.5488)*1.341
    Where 50108.120 is torque delivered and 50070.56 is rpm. The rest of the math calculates hp out of these two numbers.

    The scanner gives me readings between -50 000 and 50 000. How come?

  2. #2
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    I'm using ([50108.127]*[50070.56]/5373. Seems to work fine for me.

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    Quote Originally Posted by Tapi View Post
    The scanner gives me readings between -50 000 and 50 000. How come?
    Because your formula is wrong?

    I've been using ([50108.127]*[50070.56])/5252
    as have others on here.
    Always felt it read a bit too high..
    Think I might try SVT_Z06's formula..
    seems it'll drop the HP figure to something a bit lower and more realistic.

    Would be good if you show us dyno/scanner HP differences after you fix your formula/problem, Tapi + tell us what motor and mods..
    See how accurate this thing is..

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    My formula is for HP from torque in Newton Meters. (Torque in Nm) X (RPM) divided by 9.5488 gives horsepower in kilowats (kW). 1 kilowat is 1.341 X hp.

    That 50108.127 vs 50108.120 might be the torque in Nm and in lbf?

    Anyway, since my math doesn't work in HPtuners, I'll make something out of those formulas you suggested.

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    This ([50108.127]*[50070.56]/5373 seems to work for me. I'll figure out a correct multiplier after I get this particular car to dyno. Now it seems to show some 30-50 hp too much.

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    Quote Originally Posted by Tapi View Post
    My formula is for HP from torque in Newton Meters. (Torque in Nm) X (RPM) divided by 9.5488 gives horsepower in kilowats (kW). 1 kilowat is 1.341 X hp.

    That 50108.127 vs 50108.120 might be the torque in Nm and in lbf?
    Where did you get that information/formula from?
    If you're getting figures of over 40,000.. and everyone else is dividing by around 5,300 instead of 9.5.. then it's clearly wrong.. and the problem (9.55).

    Eg.
    400Nm x 6000rpm / 5,300 = 453hp (sounds about right)
    your way..
    400Nm x 6000rpm / 9.55 = 251,309hp (sounds very wrong)

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    400Nm x 6000rpm / 9548.8 = 251.340 kW

    251.340 kW x 1.341 = 337.047 hp.

    Sorry for 9.5488, it was supposed to be 9548.8.
    Last edited by Tapi; 04-23-2017 at 03:21 PM.

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    Quote Originally Posted by Tapi View Post
    400Nm x 6000rpm / 9548.8 = 251.340 kW
    I like that. Seems more accurate than the formula I use + I prefer kw's anyway. Gonna change my math to ([50108.120]*[50070.56])/9548.8 tomorrow. See how far off to reality I think it is, then adjust it. Should've done this months ago.
    Last edited by Mr. Smith; 04-24-2017 at 05:08 AM. Reason: .

  9. #9
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    My thoughts on these engine power formulas..

    ([50108.127]*[50070.56])/5252 = reads too high (hp) (so /5373 would be more accurate)

    ([50108.120]*[50070.56])/9548 = reads too low (kW)

    ([50108.120]*[50070.56])/8000 = reads about right (kW)

    For my LS1 anyway..

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    Now I found time to get back in to this. The car gave 404 hp / 536 Nm on hub dyno the other day (a disappointment at every scale but that's not important now).

    I drove a WOT run on the street on second or third gear and on that same rpm the dyno showed 536 Nm, the log showed 600 Nm. This gives a number 1.1194029851 to divide the result with. I did a "calculated engine torque" math with this (61001): [50108.120] / 1.1194029851. This seems to work at least for this specific car (Corvette '97).

    Then I made a "Calculated engine HP" math: ([61001]*[50070.56])/5373. This doesn't show anything. I removed those [ and ] from around 61001 and I got numbers but they were about 8000 at idle so the math doesn't work.

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    Why did you put "([61001]" instead of "([50108.127]"

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    That 61001 is torque math which takes into account the error that comes with Engine torque ("sensor") that would otherwise be in use. If I use generic torque info from PCM, it will show too high torque numbers and that will result wrong power numbers too.

    61001= [50108.120] / 1.1194029851

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    I think I finally see what you're doing wrong..
    You're forgetting the ".unit ID" on the end of "50108".. or "61001".
    The ".120" on the end of 50108 for example represents kW
    the ".127" on the end of "50108" = hp
    ".120" doesn't mean 3 decimal points of/after 50108.

    Umm, I just took a quick look at Quantities & Units in the Scanner, and under "Torque",
    Nm (also) = .120
    and
    lb-ft (also) = .127

    oh what..
    Just checked "Power"
    and hp = 82
    kW = 81

    since when
    So we've all had torque unit ID's in our power gauges


  14. #14
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    So what is the "unit ID" for my math 61001? That number shows in the self-made math section but there is no ID shown.

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    Like I wrote..
    kW = .81
    hp = .82
    Nm = .120
    lb-ft = .127
    so it's whatever you want it to be.
    Just add one of those units/numbers to the end of 61001 or 50108 and go from there.

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    oh if it's that easy... Thanks. I'll try it.

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    Still won't work!

    This math: ([61001.120]*[50070.56])/5373
    in which the 61001.120 is calculated torque (61001.120 = [50108.120] / 1.1194029851) in which the divider 1.119... is proven value to show the torque accurately in this spesific car.
    That 50070.56 is engine speed (RPM).

    I can't get the value to graphs or histogram.

  18. #18
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    What formula are you actually using? Are you trying to reference a math parameter inside another math parameter? I can't tell.
    Post a log and tune if you want help

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  19. #19
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    Quote Originally Posted by schpenxel View Post
    Are you trying to reference a math parameter inside another math parameter?
    Yes I am.

    I've got a math parameter showing torque precisely as it's shown in dyno and now I try to use that same parameter as a base for accurate hp.

  20. #20
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    You can't do that.

    Replace the math parameter with whatever formula it's using in the previous math parameter instead.

    You can't reference math parameters inside of other math parameters
    Post a log and tune if you want help

    VCM Suite V3+ GETTING STARTED THREADS / HOW TO's

    Tuner by night
    CPX Tuning
    2005 Corvette, M6
    ECS 1500 Supercharger
    AlkyControl Meth, Monster LT1-S Twin, NT05R's
    ID1000's, 220/240, .598/.598, 118 from Cam Motion

    2007 Escalade, A6
    Stock