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  1. #1

    The higher the RPMs the better!

    Help me understand. I read a lot of posts that seem to indicate folks believe any mod that results in gaining engine speed is always a good thing becuase it means you gained watercraft vehicle speed. It seems to me if the goal is to maximize watercraft speed, that when a mod is completed that the engine speed that maximum power is achieved must be known, and then to select the appropriate impeller. In other words, if the engine speed is allowed to go above where peak power is achieved, the watercraft speed is less than it could be. Raising the rev limit, installing light wieght train train parts etc etc has it's place, IF the engine is being operated at the correct speed. Am I missing something here?


  2. #2
    imp0ster's Avatar
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    Quote Originally Posted by Joeypwc View Post
    Help me understand. I read a lot of posts that seem to indicate folks believe any mod that results in gaining engine speed is always a good thing becuase it means you gained watercraft vehicle speed. It seems to me if the goal is to maximize watercraft speed, that when a mod is completed that the engine speed that maximum power is achieved must be known, and then to select the appropriate impeller. In other words, if the engine speed is allowed to go above where peak power is achieved, the watercraft speed is less than it could be. Raising the rev limit, installing light wieght train train parts etc etc has it's place, IF the engine is being operated at the correct speed. Am I missing something here?
    on a stock craft you want to keep the RPMs at 8150, 50rpm below the rev limiter. You accomplish this with impeller pitching and nozzle adjustments. The HP doesn't end at 8200rpms. It's limited to keep the factory engine together. The only way people spin higher is with a reflash and upgraded valvetrain and with the reflash comes more HP to help you get in the upper RPMs. Again with the reflash you need to run less impeller to get to the desired RPMs.
    Last edited by imp0ster; 03-20-2013 at 12:03 PM.

  3. #3
    Boost-A-Holic's Avatar
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    little confused by how you said this but i think i know what your trying to say. As far as getting the right revs for your mods i know that with a stock ECU on my RXP you really cant go any further than 8200 so if your modding your boat and bouncing off the rev-limiter all day you need to re-pitch/swap props for one that puts you right under the limiter so that your actually utilizing your powerband gaining speed and not just boucning off the limiter. If you have an aftermarket ECU or tune than you can set your target RPMs way higher assuming your motor can take it. But just like with the Stock ECU on an aftermarket one you want to set your revs right below the limiter and not bouncing on it.


    Hope this helps

  4. #4
    warsawspeedfreak's Avatar
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    Its not only that but, your engine must make enough power to push the rpms higher than stock levels. As you add more boost by using a bigger charger for example you will increase the maximum achievable rpm. Then you pitch your prop to get it dialed in to the preferred rpm based on your ecu choice and supporting mods... Just because you raise your rpm limit doesn't necessarily mean your engine combo will push it that far...

    I think the general rule is 100-200 rpms off your rev limiter to be safe so your ecu doesn't pull timing and run your engine into a lean condition. This is the simple version of this but there is much more going on electronically once you hit the limiter...Others know more than I and maybe will chime in...

  5. #5
    You said "The HP doesn't end at 8200rpms.It's limited to keep the factory engine together. "

    Do you mean that the peak horsepower occurs at a higher engine speed than the rev limiter and this is done prevent engine failure? I find that really surprising. I can't say I have ever seen an engine set up like that with the exception of governers like the SeaDoo learning key which is used to limit performance, not to protect the engine.

    Every engine I have ever seen developes maximum horsepower at a certain engine speed and anything past the the horsepower decreases (technically maximum power occurs at a speed that moves around a little bit but for this discussion let's leave keep it simple.)


    Quote Originally Posted by imp0ster View Post
    Quote Originally Posted by Joeypwc View Post
    Help me understand. I read a lot of posts that seem to indicate folks believe any mod that results in gaining engine speed is always a good thing becuase it means you gained watercraft vehicle speed. It seems to me if the goal is to maximize watercraft speed, that when a mod is completed that the engine speed that maximum power is achieved must be known, and then to select the appropriate impeller. In other words, if the engine speed is allowed to go above where peak power is achieved, the watercraft speed is less than it could be. Raising the rev limit, installing light wieght train train parts etc etc has it's place, IF the engine is being operated at the correct speed. Am I missing something here?
    on a stock craft you want to keep the RPMs at 8150, 50rpm below the rev limiter. You accomplish this with impeller pitching and nozzle adjustments. The HP doesn't end at 8200rpms. It's limited to keep the factory engine together. The only way people spin higher is with a reflash and upgraded valvetrain and with the reflash comes more HP to help you get in the upper RPMs. Again with the reflash you need to run less impeller to get to the desired RPMs.

  6. #6
    I totally agree an engine should not be run real close to the rev limiter for any length of time...that would be a great way to "go boom" as they say.

    Quote Originally Posted by warsawspeedfreak View Post
    Its not only that but, your engine must make enough power to push the rpms higher than stock levels. As you add more boost by using a bigger charger for example you will increase the maximum achievable rpm. Then you pitch your prop to get it dialed in to the preferred rpm based on your ecu choice and supporting mods... Just because you raise your rpm limit doesn't necessarily mean your engine combo will push it that far...

    I think the general rule is 100-200 rpms off your rev limiter to be safe so your ecu doesn't pull timing and run your engine into a lean condition. This is the simple version of this but there is much more going on electronically once you hit the limiter...Others know more than I and maybe will chime in...

  7. #7
    imp0ster's Avatar
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    Quote Originally Posted by Joeypwc View Post
    You said "The HP doesn't end at 8200rpms.It's limited to keep the factory engine together. "

    Do you mean that the peak horsepower occurs at a higher engine speed than the rev limiter and this is done prevent engine failure? I find that really surprising. I can't say I have ever seen an engine set up like that with the exception of governers like the SeaDoo learning key which is used to limit performance, not to protect the engine.

    Every engine I have ever seen developes maximum horsepower at a certain engine speed and anything past the the horsepower decreases (technically maximum power occurs at a speed that moves around a little bit but for this discussion let's leave keep it simple.)


    Quote Originally Posted by imp0ster View Post
    Quote Originally Posted by Joeypwc View Post
    Help me understand. I read a lot of posts that seem to indicate folks believe any mod that results in gaining engine speed is always a good thing becuase it means you gained watercraft vehicle speed. It seems to me if the goal is to maximize watercraft speed, that when a mod is completed that the engine speed that maximum power is achieved must be known, and then to select the appropriate impeller. In other words, if the engine speed is allowed to go above where peak power is achieved, the watercraft speed is less than it could be. Raising the rev limit, installing light wieght train train parts etc etc has it's place, IF the engine is being operated at the correct speed. Am I missing something here?
    on a stock craft you want to keep the RPMs at 8150, 50rpm below the rev limiter. You accomplish this with impeller pitching and nozzle adjustments. The HP doesn't end at 8200rpms. It's limited to keep the factory engine together. The only way people spin higher is with a reflash and upgraded valvetrain and with the reflash comes more HP to help you get in the upper RPMs. Again with the reflash you need to run less impeller to get to the desired RPMs.
    I don't know where the 4tec makes it's greatest HP. It is limited like that from the factory to keep itself together. The 260 is also limited but with a steeper prop. Of course every engine develops max HP somewhere. I'm saying the stock springs are only good for about 8300rpm and for the sake of warranty and mass production they limited the craft at 8200rpm and we shoot for 8150 to keep off the rev. Once you hit the rev if you even slightly come unhooked it just drops power. With just a few mods you can push well past 8200 on a stock prop, they just cap it.

    BTW painting things orange in your engine bay on a SeaDoo gets you more rpm and speed. I could have never hit what I did without it.

  8. #8
    mac_man_luke's Avatar
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    S/C 4tecs keep making more power the higher the RPM.

    This is because the more power you make, the faster the super charger spins = more boost.

    Im sure there is a point where this will run out but there have been skis run up/over 10,000rpm.

  9. #9
    OK, I agree orange paint makes rpm and speed! Keep this a secret, but I'm going to paint the pistons in my new ski orange. I plan on turning high rpm, so it will be light orange!

  10. #10
    I'm having a tough time with that. I don't believe a motor can simply be spun faster and make more power, supercharger of not.

    My gut says if a dyno is hooked up to a stock 4-tec 260, maximum horsepower will occur right around 8000 rpm or so. Less than the 8200 rev limit.




    Quote Originally Posted by mac_man_luke View Post
    S/C 4tecs keep making more power the higher the RPM.

    This is because the more power you make, the faster the super charger spins = more boost.

    Im sure there is a point where this will run out but there have been skis run up/over 10,000rpm.

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