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  1. #1
    Site Admin Green Hulk's Avatar
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    Elevation and climate 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:
    http://www.greenhulk.net/forums/show...light=pitching

    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
    http://www.wallaceracing.com/braking-hp.php



    Hope this helps you guys!
    Jerry


  2. #2
    JT jpt7779's Avatar
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    Jerry's post with Charlie's spread sheet is very accurate. Elevation can also be referred to as RAD, Relative Air Density and plays a significant role in how your engine performs. Here is more info along the same lines from my previous posts years ago:

    Check this out:http://wahiduddin.net/calc/calc_hp.htm

    Enter some basic weather info and you will see dramatic effects on Horsepower and RAD - relative air density. You will find that cool air temps, high pressure 30.00 and above, low humidity, low dew points will yield 100% plus horsepower.

    Conversely, hot air temps, high humidity, high dew points, high RAD #'s, LOW pressure below 29.92 will yield poor performance.

    This is why you will see 150-200 rpm changes day to day with big weather changes - it really does make a huge impact!


  3. #3
    Sanfish's Avatar
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    About time this was brought up, hopefully all these mod expectations will be compared with equal apples.

    When I make hits, I will always log the A/D (air density/psi) because without this information, you can't fairly compare run after run. Here in Florida, I've seen massive changes as a storm comes within several miles of test spot. This happened to me one time while I was tuning and wasn't paying attention to the A/D (pressure), screwed up the whole day tunes because the next week, everything was off (AFR).

    The attached picture is probably as good as it gets in South Florida (anything near 30.2 pressure is pretty rare = around 1020hPa). Notice the density altitude!!!. This screenshot was taken January during a Florida winter. When you have a day like that, you make test hits because that's as good as its going to get (bragging rights)
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  4. #4
    Site Admin Green Hulk's Avatar
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    Gotta love those negative density altitude days! I call that "mineshaft air"

  5. #5
    The formula is not percentage, but horsepower lost. At my usual 5000 ft elevation lake, by your calculations, my 260 would have only 150 hp. Here is a good read from e3
    http://e3sparkplugs.com/how-to-calcu...r-snowmobiles/
    as you can see, the formula given is not a percentage, rather a total hp lost. Your example above would be a loss of 13.5 hp, not 13.5%.

  6. #6
    ptscon's Avatar
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    How about timing at elevation? Should there be any changes done to, safely, improve performance when you're above sea level?

  7. #7
    Site Admin Green Hulk's Avatar
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    Quote Originally Posted by Wire4Money View Post
    The formula is not percentage, but horsepower lost. At my usual 5000 ft elevation lake, by your calculations, my 260 would have only 150 hp. Here is a good read from e3
    http://e3sparkplugs.com/how-to-calcu...r-snowmobiles/
    as you can see, the formula given is not a percentage, rather a total hp lost. Your example above would be a loss of 13.5 hp, not 13.5%.
    I think you are right and I have edited my post. I have seen in explained both ways, in percentage and as actual HP losses which lead me to the conclusion HP loss was in percentage. One such example: http://my350z.com/forum/engine-and-d...n-formula.html

  8. #8
    Quote Originally Posted by Green Hulk View Post
    Quote Originally Posted by Wire4Money View Post
    The formula is not percentage, but horsepower lost. At my usual 5000 ft elevation lake, by your calculations, my 260 would have only 150 hp. Here is a good read from e3
    http://e3sparkplugs.com/how-to-calcu...r-snowmobiles/
    as you can see, the formula given is not a percentage, rather a total hp lost. Your example above would be a loss of 13.5 hp, not 13.5%.
    I think you are right and I have edited my post. I have seen in explained both ways, in percentage and as actual HP losses which lead me to the conclusion HP loss was in percentage. One such example: http://my350z.com/forum/engine-and-d...n-formula.html
    I figured something was wrong because I've ridden 150hp machines at sea level, and my rxpx is definitely more than that at 5000'.

  9. #9
    Quote Originally Posted by ptscon View Post
    How about timing at elevation? Should there be any changes done to, safely, improve performance when you're above sea level?
    I would be interested about this as well.

  10. #10

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    Will these superchargers/ECU compensate for altitude like a turbo snowmobile will? Or is adding more boost to make up for altitude loss an adjustment you'd have to make with a tune?

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