Power calculation

Discussion in 'Forced Induction & Tuning' started by Dalamar, Jul 11, 2006.

  1. Dalamar

    Dalamar Post Whore Retired Staff SN95 Supporter

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    Do you ever find yourself saying:

    "how much power will this add?"
    "how much boost should I run?"

    I find this equation handy:
    [(boost / 14.7) +1] x base HP

    best to add rear wheel HP because it accounts for your drive train loss.
    plug in base HP and boost - this is very close to what your power will be.


    Other factors to keep in mind:
    posative displacement or roots type blower will give you a longer torque curve.
    Centifical gains are more on the top (obviously)
    Turbo's are a little different because they don't take power off the crank to operate.


    Hope you guys find this info helpfull. ;D
     
    bikeboy636 likes this.
  2. Dalamar

    Dalamar Post Whore Retired Staff SN95 Supporter

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    no comments?

    does anyone find that interesting, or helpful?
     
  3. MeanGrn Gt

    MeanGrn Gt Well-Known Member

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    definetly helpful/informing its nice to have a idea of what you will make when comparing options... but im going with a 347 h/c/i instead of boost
     
  4. Spyder

    Spyder Active Member

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    yeah, for anyone using this equation on a supercharger, your actual numbers will be lower for the parasitic loss due to the belt, like Dalamar said. But its actually pretty accurate, at least when comparing the numbers in magazines before and after the install something cool.
     
  5. 95KBGT

    95KBGT Legend

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    wow...

    11psix14.7+1)x 185= 323

    i got some work to do
     
  6. Lightning Struck

    Lightning Struck Post Whore

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    Its a good way to get a idea of where you would be, not quite right for KBGT however
     
  7. Dalamar

    Dalamar Post Whore Retired Staff SN95 Supporter

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    What's not right??

    I just double checkit agains my friend who just did a PI swap, has a Vortec and it's right on.
     
  8. Lightning Struck

    Lightning Struck Post Whore

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    his numbers are under what the formula gives :dunno:
     
  9. Dalamar

    Dalamar Post Whore Retired Staff SN95 Supporter

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    hmm, sounds like somethings off a bit.
    if you plug in actual rear wheel power, and actual boost it's right on.


    Here's my cousins info - he just got it dyno'd yesterday.
    98 GT, hedders, vortec running 5 psi.

    He was putting down 262 to the wheels on the NPI heads, with the blower.
    NA power was around 185

    He did the PI headswap, same 5# of boost, he dyno'd 335 to the wheels.
    work that backwords and he's NA putting down 250 HP NA.

    this is with an 8# pulley - the thinner air at Denver's altitude makes it 5#

    If he runs 9# he will be at 403 to the wheels. :)
     
  10. Dalamar

    Dalamar Post Whore Retired Staff SN95 Supporter

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    Clarification:

    This is for superchargers on engines with stock or mild cams.

    Changing the cam specs will chang the flow ratios.
    Also with a turbo, the numbers are considerably better.
    :)
     
  11. Spyder

    Spyder Active Member

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    You have to take into account that with this calculation, it will give you the numbers without the parasitic loss of the supercharger. Unfortunatly, all superchargers, be it centri or posi, with have some parasitic loss. Thats why the numbers are high for 95KBGT.

    Now when using this equation on a turbo car, its near dead on.
     
  12. Lightning Struck

    Lightning Struck Post Whore

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    that makes good logic :)
     
  13. Dalamar

    Dalamar Post Whore Retired Staff SN95 Supporter

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    Actually Spyder it's not,
    If that were true, I'd have to push 35PSI to hit 700 HP.
    According to Heath, 18# will do it...

    It's accurate for supercharged cars, without radical cam upgrades.
     
  14. Lightning Struck

    Lightning Struck Post Whore

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    all these numbers is confusing :-\
     
  15. Dalamar

    Dalamar Post Whore Retired Staff SN95 Supporter

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    yes they are.

    If it was easy, everyone would have 500 HP cars. :-\
     
  16. Spyder

    Spyder Active Member

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    No, its true, ive compared alot of before and after dyno numbers and its true.

    If you put down 300 n/a and then thrwo on 18 psi of turbo, use the equation

    (18/14.7)+1= 2.225 300(n/a hp) x 2.225 = 667 which is close enough to 700

    The formula is damn near correct for turbos, but its not right for supercharger.

    Just for shits and giggles, 35 psi on your 300 N/a combo would net 1014 accoding to the equation.
     
  17. Dalamar

    Dalamar Post Whore Retired Staff SN95 Supporter

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    I guess the Compression throws a curve in there.
    9:1 rear wheel estimated at 260. I won't know until it's on the dyno :)
    I'll have to ask Heath.

    The formula was real close on Ryan's Vortec numbers before / after the headswap??
     
  18. Dalamar

    Dalamar Post Whore Retired Staff SN95 Supporter

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    OK, this is for real.
    If you do the leaf blower install, it's right on :thumb:
     
  19. Dalamar

    Dalamar Post Whore Retired Staff SN95 Supporter

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    That should say 25, not 35. :hammer:

    Spyder and I are debating this on messanger....
    The formula is based off NA rwhp, changing parts will effect it.
    more to come...
     
  20. Lightning Struck

    Lightning Struck Post Whore

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    Ok :thumb: