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  1. #1

    Taking Baseline measurements before modifications

    I too am looking very seriously at getting one of the new 250s. I've never modified my previous jetskis, as I didn't feel I was going to get a great deal of gain for the effort. However, with the new 250 I believe this is going to be different.

    With modifications to turbo-charged motor cars, I've never just simply by-passed (or removed) a muffler. I have always done back pressure tests to see which mufflers are in fact giving me the most back pressure. I note that people are by-passing the secondary muffler i.e. the riva kit, but for all we know, the main source of back pressure could well be the first muffler. The second could simply be like a resonator i.e. all you're really doing is simply making the ski louder with very little gain indeed. The only way you can really tell is by checking back pressure.

    Likewise, with the air box, I have always checked, with a manometer, the level of vacuum e.g. if the standard air box has 6" or less of vacuum under wide open throttle, you know you're not going to get much benefit from changing.

    I'm just thinking out aloud and am curious as to your thoughts regarding the above.


  2. #2
    Unlike cars watercraft runs water through the exhaust. By removing the second muffler it minimizes the water biuld up on idle.

    The exhaust mod from Riva has been tested. It works because every modified 15F SC uses it or a simular mod.

    The primary muffler on mine will also be modified. TJ does a surgery on it and buttons it back up then sends it back to you. I dont know what it is he does but it works.


    Most modifications will help with performance. It may not be the same results as a car but they do work. Instead of getting to far into pressure and dyno specs, just try it, if it works then great. If your reserved about testing then let guys like myself do the test for you.

  3. #3
    Yellow93's Avatar
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    What you are talking about is true, on a turbocharged application the backpressure can be VERY important... remember, the supercharger is ran off a belt, not spent gasses as a turbocharger is! I think gains will be seen removing the secondary muffler...

  4. #4
    Man i totally over read that. Good piont.

  5. #5
    Hydrotoys's Avatar
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    I think it will sound really, really cool, and get rid of that fuggin sewing machine sound. As long as it doesn't negatively effect the performance of the ski, I'm all for it!

    "Before and After" will be fairly difficult. A lot of us folks that have done mod changes in the past, KNOW that you can't do a mod change one day, and then go do "back to back" testing the next week. The weather won't allow it. You must do your best-guess using some type of rad gauge and some accurate weather conditions. While the window of variability is narrower with a SC engine, it IS still there. IMHO, Any before/after data MUST be followed with corrected alttitude or it is just guesswork.

    We see it all the time on the forums... "I changed the part and gained .5mph. Well, did you really? Or was the weather better that week? Was your gas fresher? Was your riding position different?

    About measuring back pressure....GOOD LUCK. Even if you did measure correctly backpressure, you can not simulate engine load, exhaust pulses, and even water-supply into the exhaust. When someone post up some data about back-pressure, no real world conditions apply. In short, it's a great reference, but to what?

    Your GPS and your lap-timer on your own private course might be your best friend when it comes to these changes.

    It is doable, but it's not easy to be accurate. New models always bring out the optimist...especially when they just paid $11k for it. Keep your head on your shoulders, and use a notebook for all your changes. Take notes on Corrected Altitude and rider weight, and even things like water temps and wind. Try to test in the same spot every time. Take a PDA or laptop with you, and use a simple program like this to figure out your CA. Use local weather info, or better yet, buy a portable weather station.

    http://www.hydrotoys.com/wavs/pda-de...a-denscalc.htm

    Good luck.

  6. #6
    way2fast's Avatar
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    Changes to the exhaust will make it sound different, but the sewing machine sound will always be there because it is coming from the motor not the exhaust. When sitting right on top of the engine, you can't get away from hearing it. Maybe if the exhaust is made loud enough it will drown the engine noise out.

    Richard

  7. #7
    Hydrotoys's Avatar
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    Maybe if the exhaust is made loud enough it will drown the engine noise out.
    Well, YEAH, of course!

  8. #8
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    I use an engine dyno (900hp max) to test. Today i finished and sent off to heat treat a new input shaft for this application and a few other skis to test.

    I’m thinking of a free dyno day to a Kaw 250 owner, then you'll get the real deal. any takers E-mail me...

    NO tire kickers please.

    Shawn

    [email protected]

  9. #9
    Formerly Ultra250 TN Aquaholic6801's Avatar
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    Nitro,
    Might be interested in the free dyno day.Just waiting on my ski to arrive, I have a few mods here in the garage wating on the ski and the break in.

  10. #10
    Been around for years...seen it all Kawi-Guy's Avatar
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    Wow, sounds like a great idea.
    Thanks Nitro for stepping up !!

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