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  1. #1

    Change impeller or New tune?

    So my ski is finally running right - 19' GP1800 w/ the below mods

    “Ultimate” CAI from Greenhulk
    Riva Engine Breather Kit
    Riva Cooling Upgrade
    Solas 13/18 Prop blueprinted/balanced by Impros
    Riva Thru-Hull Exhaust
    Riva Titanium Valve Spring Retainers
    MTX Wideband AFR Sensor
    MaptunerX - Stage 1 8500

    Only am seeing 79.1 MPH on the gps, but hard on the rev limiter. Should i do a taller prop, or go with a different tune/higher rev limit? Looking for low/mid 80's. Fizzle coming this winter.


  2. #2

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    since you have valve retainers in place I would raze the rev limiter to 9000 and retest ski first to see if you can get closer to 8800 to 8900 rpms if you are on the limiter hard you can not get the best out of your ski.

  3. #3
    Click avatar for tech links/info K447's Avatar
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    Quote Originally Posted by IanM88 View Post
    So my ski is finally running right - 19' GP1800 w/ the below mods

    “Ultimate” CAI from Greenhulk
    Riva Engine Breather Kit
    Riva Cooling Upgrade
    Solas 13/18 Prop blueprinted/balanced by Impros
    Riva Thru-Hull Exhaust
    Riva Titanium Valve Spring Retainers
    MTX Wideband AFR Sensor
    MaptunerX - Stage 1 8500

    ... Fizzle coming this winter.
    You are using the MaptunerX Stage 1 Plus tune, correct?

    What octane fuel?

    With the Fizzle intercooler, you might want both a higher RPM limit and a repitched impeller.

  4. #4
    Site Admin Green Hulk's Avatar
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    Quote Originally Posted by IanM88 View Post
    So my ski is finally running right - 19' GP1800 w/ the below mods

    “Ultimate” CAI from Greenhulk
    Riva Engine Breather Kit
    Riva Cooling Upgrade
    Solas 13/18 Prop blueprinted/balanced by Impros
    Riva Thru-Hull Exhaust
    Riva Titanium Valve Spring Retainers
    MTX Wideband AFR Sensor
    MaptunerX - Stage 1 8500

    Only am seeing 79.1 MPH on the gps, but hard on the rev limiter. Should i do a taller prop, or go with a different tune/higher rev limit? Looking for low/mid 80's. Fizzle coming this winter.
    You have the retainers so just raise the limiter.

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  6. #5
    Had Jesus do the Stage 1 Plus tune with modified limiter to 9K Results as follows

    Did 5 passes after a proper warm up : 55 Degrees, 59.7 Degree Water Temp, Wind 14mph
    Half tank of gas (93)

    RPM's ranged from 8730-8830 Neutral Trim

    Best top speed of 82.1MPH

    Definitly happy - but Given the RPM's - shouldn't I be seeing higher top speeds? Would the AGT tune pick up a few more mph?

  7. #6

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    given the fact that you stated 14 mph winds the water had to be chopped up and that a lone can cost you mph. plus dealing with windy conditions cost you speed as well, since it is cool conditions now you may want to decrease your prop 1/2 pitch when summer heat hits you will easy loose another 200- 300 rpms.

  8. #7
    Quote Originally Posted by IanM88 View Post
    Had Jesus do the Stage 1 Plus tune with modified limiter to 9K Results as follows

    Did 5 passes after a proper warm up : 55 Degrees, 59.7 Degree Water Temp, Wind 14mph
    Half tank of gas (93)

    RPM's ranged from 8730-8830 Neutral Trim

    Best top speed of 82.1MPH

    Definitly happy - but Given the RPM's - shouldn't I be seeing higher top speeds? Would the AGT tune pick up a few more mph?

    14mph wind is nowhere near ideal conditions, with the tailwind your numbers are skewed as well as skewed with the headwind.

    Neutral trim also leaves some MPH on the table, my ski performs best top speed with nose up.

    My Stage 1 plus(8500rpm) AGT does same as you in 90 degree air/85 degree water temps, dont be discouraged. I think your numbers are off because of wind and trim, get those fixed and I believe you will see 3 more MPH. The retainers do nothing expect prevent you from dropping a valve, no power or speed to be gained.


    Shop who I deal with here repitched a prop to 17.5 and saw a increase in MPH and incredible pull out of the hole and thru midrange. Its a Stage 2 ski with Fizzle and retainers. They ride buoys and not after top speed, I personally would not do it if your a top speed racer. The higher the RPMs the higher the risk of breakage. Thats just my opinion

  9. #8
    The higher the RPMs the higher the risk of breakage. [/QUOTE]

    Go big or go home...lol

  10. #9
    Quote Originally Posted by yellow jacket View Post
    The higher the RPMs the higher the risk of breakage.
    Go big or go home...lol[/QUOTE]

    Not Jet Ski but Im still licking the wounds from last big attempt

  11. #10
    butterbean_29512's Avatar
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    If you have the retainers, and not turning higher RPM's, you are wasting a little horsepower due to the increased tension on the springs. The engine has to expend horsepower to turn things such as the camshaft, etc, and if you're expending extra horsepower without turning the extra PRM's it's a waste of power. Not much, and probably not enough to worry about, but it's still power not used to turn the impeller.

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