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  1. #1

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    When Does Supercharger Really Start To Work?

    Just as it says. Is it true that up until the ski hits 5500 rpm the supercharger really isn't doing anything, in other words making no boost and behaves the same a N/A ski would? I have a 12 FX Cruiser SHO but in general if we are talking about all supercharged skis? Just curious.....


  2. #2
    AWA MEMBER
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    mine starts at 6k rpm

  3. #3
    Kelly_A's Avatar
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    Quote Originally Posted by mjealey View Post
    Just as it says. Is it true that up until the ski hits 5500 rpm the supercharger really isn't doing anything, in other words making no boost and behaves the same a N/A ski would? I have a 12 FX Cruiser SHO but in general if we are talking about all supercharged skis? Just curious.....
    Seems counterintuitive that it's wouldn't help some at lower RPMs. But, you can sort of think about the SC as a small box fan operating with very stiff wind behind it. If you don't turn the fan on high, you're not going to feel it at all.

    Up to about 5k rpm, the volume of the air being pulled into the engine through normal combustion is greater than the SC impeller output. As RPMs increase, the impeller pushes more & more air into the engine. Impellers are designed to work in a targeted RPM range. Boost is of less value, performance wise, at low RPMs. So, impeller designers target the upper half to third of the engine's useable RPMs range - where boost provides the most bang for the buck. Skis with engines that run higher RPMs will begin build boost a little later.

  4. #4
    Quote Originally Posted by Kelly_A View Post
    Quote Originally Posted by mjealey View Post
    Just as it says. Is it true that up until the ski hits 5500 rpm the supercharger really isn't doing anything, in other words making no boost and behaves the same a N/A ski would? I have a 12 FX Cruiser SHO but in general if we are talking about all supercharged skis? Just curious.....
    Seems counterintuitive that it's wouldn't help some at lower RPMs. But, you can sort of think about the SC as a small box fan operating with very stiff wind behind it. If you don't turn the fan on high, you're not going to feel it at all.

    Up to about 5k rpm, the volume of the air being pulled into the engine through normal combustion is greater than the SC impeller output. As RPMs increase, the impeller pushes more & more air into the engine. Impellers are designed to work in a targeted RPM range. Boost is of less value, performance wise, at low RPMs. So, impeller designers target the upper half to third of the engine's useable RPMs range - where boost provides the most bang for the buck. Skis with engines that run higher RPMs will begin build boost a little later.
    That's interesting. I always thought that the beauty of a supercharger was that they generate instant boost from the get go unlike turbo's that suffer from turbo lag depending on their size.

  5. #5
    SurfRider's Avatar
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    When Does Supercharger Really Start To Work?

    Quote Originally Posted by slingshot View Post
    That's interesting. I always thought that the beauty of a supercharger was that they generate instant boost from the get go unlike turbo's that suffer from turbo lag depending on their size.
    There are different type of SCers. The "roots" style, like found in the Kawi's make boost all the time. The "centrifugal", in the Yami and Doo's only make boost when the reach their optimum RPM. You can think of this type like a turbo wheel as they are essentially the same (but mechanically driven by the motor instead of exhaust).

  6. #6
    yamahamiamiski's Avatar
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    from the way the sc ski accelerate you would think the boost is there pretty quick

  7. #7
    SurfRider's Avatar
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    That's the beauty of having a terrible pump.

    It cavitates so quick off the line that it comes up to 6000 RPM within a split second. lol.

  8. #8
    Kristian Keppel Waterholics's Avatar
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    So then why do people complain about turbo lag on some turbo skis. If boost comes on in a turbo at let's say a 2-4000 RPM's on a properly sized turbo for our engine, then it should have better acceleration than a S/C ski ?

  9. #9
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    Because of the difference between the SC and Turbo methods of turning the impeller wheel. A SC is mechanically driven directly from the motor. So the SC will spin up exactly the same rate as the motor. The Turbo works off of the Exhaust. So the exhaust has to build up enough strength to start spinning the wheel inside the exhaust, which in turn turns the impeller wheel to built boost. That takes more time.

  10. #10
    abracadabra's Avatar
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    As soon as you start the engine. It will affect/change the compression ratio of the engine as soon as you start the engine, Julio...

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