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  1. #1
    Site Admin Green Hulk's Avatar
    Join Date
    Apr 2005
    Morgan City, LA

    Elevation and how it affects engine performance and impeller pitch

    We see all the time how one forum members ski with the same mods may run better than another ski in another part of the country or world. A big factor that causes this is ambient temperature differences and most importantly ELEVATION!

    A big mistake I see many people make is they think they can install an impeller right out the box and expect perfect results. This is not always the case, people lose speed, because they lost RPM and they quickly blame the impeller for being "junk" or the pitch being wrong right out of the box.

    One thing we've learned over the years is no one impeller pitch is going to be just right for every ski in every geographical location. If you think you will install an impeller and RPM be perfect on your ski right out the box you are setting yourself up for disappointment.

    If you want the most out of your ski you will have to fine tune your impeller for optimum rpm which will provide for best results. Afterall, RPM = speed.

    Pitching your impeller is EXTREMELY easy to do following these instructions on the forum. Yes, these instructions were written based off of a Sea Doo impeller, but the same exact principal applies to Yamaha and Kawasaki impellers:

    Elevation affects engine HP in a big way and the more HP your engine makes the more it's affected as the elevation increases. That said, the higher the elevation in your riding area the less impeller pitch you will want to run in order to keep the RPM's up higher. RPM = Speed. Reduced RPM = less speed!

    Here's a forumula for calculating your HP loss at your elevation. You may be shocked at just how much power your ski loses at your riding elevation.
    HP Loss = (elevation x 0.03 x horsepower @ sea level)/1000

    So for example, a Sea Doo 300 HP ski at 1500' elevation:

    1500' elevation x .03 x 300hp divided by 1000 = 13.5 HP loss

    To overcome any HP loss due to high altitdude the simple fix is to depitch the trailing edge of your impeller slightly to get the RPM up and you will benefit both from higher speed and improve acceleration.

    Here is an online calculator that will easily calculate HP losses at altitude

    Hope this helps you guys!

  2. #2
    Moderator shawn alladio's Avatar
    Join Date
    Jan 2006
    Earth, USA, California
    This is a great post Jerry. We see this at Lake Tahoe here in California when operating at lower terrain, thanks for caring and sharing!

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