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  1. #1

    Regretting 13/18

    I put on a 13/18 and have done all the supporting mods for a Riva Stage 1 plus (8500rpm) tune, Iím ecstatic about the mid range pull but rarely find myself going 100% full throttle. I just donít see much gain from 8000 to 8500 rpm but the motor screams. In 70 degree water temps and 76-80 degree temps @ 500-800 ft ASL I have a top speed of 80-82 depending on chop. I run roughly 74-76 mph @ 8000rpms.

    I donít know if I want to try and lower RPM with a lucky 13 cone, go to a 13/20 impeller or really go wild and change super charger wheel and add a boost controller. Obviously the boost controller is my number 1 pick because I can make more power down lower and use the scramble button when needed up top.


    Any of you hardcore guys have input ?

    John


  2. #2
    YAMAHA POWAAAA !!!!! 1_Fast_SHO's Avatar
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    Quote Originally Posted by TurboX View Post
    I put on a 13/18 and have done all the supporting mods for a Riva Stage 1 plus (8500rpm) tune, Iím ecstatic about the mid range pull but rarely find myself going 100% full throttle. I just donít see much gain from 8000 to 8500 rpm but the motor screams. In 70 degree water temps and 76-80 degree temps @ 500-800 ft ASL I have a top speed of 80-82 depending on chop. I run roughly 74-76 mph @ 8000rpms.

    I donít know if I want to try and lower RPM with a lucky 13 cone, go to a 13/20 impeller or really go wild and change super charger wheel and add a boost controller. Obviously the boost controller is my number 1 pick because I can make more power down lower and use the scramble button when needed up top.


    Any of you hardcore guys have input ?

    John
    Cant add no boost controller, you have a supercharger not a turbocharger. Your prop controls your rpms


  3. #3
    Quote Originally Posted by 1_Fast_SHO View Post
    Cant add no boost controller, you have a supercharger not a turbocharger. Your prop controls your rpms

    Ive done this on several vehicles, you add the waste gate to the inlet side and partially bleed off boost to maintain the preset maximum boost. In most cases it would be costly but I have a old waste gate and several boost controllers laying around. My most expensive investment would be a upgraded cooler, in theory it works as long as I have a tuner/Calibrator who can help me. I am a recreational rider and not wanting to go aftermarket Engine management and crap.

  4. #4
    Quote Originally Posted by TurboX View Post
    Ive done this on several vehicles, you add the waste gate to the inlet side and partially bleed off boost to maintain the preset maximum boost. In most cases it would be costly but I have a old waste gate and several boost controllers laying around. My most expensive investment would be a upgraded cooler, in theory it works as long as I have a tuner/Calibrator who can help me. I am a recreational rider and not wanting to go aftermarket Engine management and crap.
    Not going to work with this jetski. The supercharger shaft gear is spun by another gear attached to the crank this creates more boost as RPM's increase. Adding a wastegate like people do on centri blowers is not going to work on this design and it will over complicate things for no real benefit if it does. People are going triple digits without it. With a 13/18 you should be spinning well past 8500, sounds to me like you're on the limiter and that is why there is no gain. Do you have a tiny tach or TTO tach to verify highest RPM? Also what are you using to get your speed #'s?
    Last edited by d00m; 04-28-2019 at 02:12 PM.

  5. #5
    Nvm just re-read what you wrote so you saw a gain from 74-76mph to 80-82mph after the prop change?

  6. #6
    Quote Originally Posted by d00m View Post
    Not going to work with this jetski. The supercharger shaft gear is spun by another gear attached to the crank this creates more boost as RPM's increase. Adding a wastegate like people do on centri blowers is not going to work on this design and it will over complicate things for no real benefit if it does. People are going triple digits without it. With a 13/18 you should be spinning well past 8500, sounds to me like you're on the limiter and that is why there is no gain. Do you have a tiny tach or TTO tach to verify highest RPM? Also what are you using to get your speed #'s?

    I appreciate the input, I’m not trying to go faster. Honestly I’m trying to just make more power at a lower RPM. I guess it’s possible to put a high boost pulley on the supercharger and just not spin the motor past the RPM I want to be at.

  7. #7
    Quote Originally Posted by TurboX View Post
    I appreciate the input, I’m not trying to go faster. Honestly I’m trying to just make more power at a lower RPM. I guess it’s possible to put a high boost pulley on the supercharger and just not spin the motor past the RPM I want to be at.
    Well first you should verify where your RPM's are and make sure you are not on the limiter because that will hurt your performance and will hurt something in the long run. Your target RPM should be 8400ish, when that is squared away you can add a bigger wheel for more acceleration, not a pulley these skis do not use a pulley style supercharger. A bigger wheel will make more PSI sooner (downside is probability of you having clutch problems goes up and you will need to pitch prop up to compensate for more power) VXR cams, and VXR throttle body are mods that will give your ski more mid range.

  8. #8

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    You can always repitch to 13/19 and save a ton of money versus buying a 13/20. But if you bring the revs down so will the boost. If you don't want to go any faster and you are topping at 8500 seems like you are right on the money. You will loose some out of the hole and midrange with a 13/20.

  9. #9
    Rook87's Avatar
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    Trade you my 13/20??? I'm wanting to find out what a 13/18 can do. Removing it tomorrow and was going to have it sent to get re pitched but if you wanna save some money like I do lol

  10. #10
    Quote Originally Posted by Rook87 View Post
    Trade you my 13/20??? I'm wanting to find out what a 13/18 can do. Removing it tomorrow and was going to have it sent to get re pitched but if you wanna save some money like I do lol
    PM sent

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