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  1. #1
    Red Devil's Avatar
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    Verifying Actual Horsepower

    With the reflashed ECU's, Les' B kits, Vortech S/C impellers, and all of the other bolt on mods, how does one check where the actual Horsepower of their ski lies? I am sure it is not as simple as just adding the "claimed" numbers that each mod gives. Just as I am pretty sure my GTX did not come out of the factory with the full 185 hp.


  2. #2
    EZ Dock of Long Island Shibby1485's Avatar
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    i wish there was a way to dyno test our skis also

  3. #3
    Moderator boataddict's Avatar
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  4. #4
    Moderator boataddict's Avatar
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    Like this...
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  5. #5
    Red Devil's Avatar
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    Quote Originally Posted by BOATADDICT
    http://www.land-and-sea.com/pwc-dyno/pwc-dyno.htm
    $5,400 Looks like I'll never know the true H/P of my Doo unless I find someone who already owns one of these puppies.

  6. #6
    Moderator boataddict's Avatar
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    I think that someone on here has one. I forget who though.

  7. #7
    Site Admin Green Hulk's Avatar
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    nitroshark

  8. #8
    Moderator boataddict's Avatar
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    If it bolts to the pump would the RXP rip it off the hull?

  9. #9
    supermac's Avatar
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    This curve will get you going.

    Your ski has a built in dyno of sorts. The cool part with the ski dyno, is you can measure actual horsepower that is transferred into the water.

    Horsepower is a function of RPMxTorque.
    HP Primer: http://www.epi-eng.com/BAS-PwrTrq.htm

    If you increase RPM in that equation, assuming torque stays the same, you make more HP. Theres no way around it.

    In your jet pump, torque does not stay the same for a given RPM, torque increases as well with the RPM, so its not as simple as increasing the RPM value in that equation. However, by modeling the pump torque curve, you can get a good approximation of HP change over an RPM change.

    Anyway, you plug in the numbers into the magic formula, assuming 208.9hp at 8100 RPM with a stock prop, you get:

    7900 193.7937355
    7950 197.4967013
    8000 201.2465395
    8050 205.0435448
    8100 208.8880121
    8150 212.7802361
    8200 216.7205117
    8250 220.7091336
    8300 224.7463966
    8350 228.8325956
    8400 232.9680252
    8450 237.1529804
    8500 241.3877559
    8550 245.6726466
    8600 250.0079471
    8650 254.3939523
    8700 258.830957
    8750 263.319256
    8800 267.859144
    8850 272.450916
    8900 277.0948666
    8950 281.7912906
    9000 286.5404829

    This is a rough estimate, but should be rather close. These numbers are only good for a stock prop. If you run a less steep pitch prop, then your HP is lower for a given RPM. If you run a steeper than stock prop, then your HP is higher.

  10. #10
    Hydrotoys's Avatar
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    How are you attributing hull drag, associated with weight, not to mention engine placement, and a whole host of other issues such as pump liner condition, efficiency of pump inlet tract (riva,r/d,stock,etc)???

    Then, let's just throw in the fact that hulls and friction are NOT LINEAR, neither is pump efficiency.

    God forbid we start talking things like rider weight. That one always leaves me with less horsepower.

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