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  1. #1

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    RXP with no intercooler top speed test today

    I finished assembling a ski today but didn't have an intercooler for it. Went out to test run it and, after fixing a fouled spark plug (???), it ran pretty good.

    2004 RXP, Totally stock except - no air intake at all, Riva grate, no intercooler.

    Water was 65 deg and air was 72. I weigh 190 lb and had 1 bar of fuel.

    GPS speed was 69.2 mph, and that was without any sealant on the greenhulk blockoff plate.

    I was actually surprised it went that fast. I was counting on 66-67.

    Just thought you guys might find this interesting.

    Mike


  2. #2
    jaycee's Avatar
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    Any loss of accel??

  3. #3
    home of the dislexic fingers breon's Avatar
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    i dont think the 7 psi of boost makes enough heat to worry about..most turbo and supercharger kit at that level of boost dont come with or need an intercooler ... i think the stock intercooler was more of a marketing thing.. i think removing the restriction is better for power than the minimal cooling it did.. just my opinion i know opinions are like a holes everbody has 1

  4. #4

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    Quote Originally Posted by jaycee View Post
    Any loss of accel??
    Acceleration on these things is very subjective, so I don't put much stock in what people claim. With that in mind, it's very close in acceleration to my 75 mph Stage 1+ RR impeller with a 15/20R.

  5. #5
    I think you could attribute the good numbers to the water and air being somewhat cooler than hotter. I also tested a 3 seater without the IC and lost 200 R`s bc it was hot...PR...

  6. #6
    Fast & Loud meeper's Avatar
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    Quote Originally Posted by breon View Post
    i dont think the 7 psi of boost makes enough heat to worry about..most turbo and supercharger kit at that level of boost dont come with or need an intercooler ... i think the stock intercooler was more of a marketing thing.. i think removing the restriction is better for power than the minimal cooling it did.. just my opinion i know opinions are like a holes everbody has 1
    i agree with you totally, most car apps making that little bost dont have IC's either....unless you get the upgrade

  7. #7
    Quote Originally Posted by meeper View Post
    i agree with you totally, most car apps making that little bost dont have IC's either....unless you get the upgrade
    hmmmmm, there is more volume more flow and most of the time more cylinders to distribute the heat aspect in car aplications. So wouldn`t you think that the 3 cylinder Rotax engine is affected by heat a bit more? I could be wrong...PR...

  8. #8
    All my technical knowledge is from cars, because that's the industry I work in, but some should apply to PWCs in general. Supercharged engines are less affected by heat than NA engines for two reasons. Hotter air is less dense, but that doesn't matter because the supercharger is making its own air density. Also, ambient air temperature doesn't really matter either because outlet temperatures of the supercharger are super high. (Again, car stuff here...) the outlet temperature of the supercharger on my drag car, before the intercooler, is almost 300 degrees. I can see changes in water temperature making a bigger difference on intercooled craft because that's what we use to cool the outlet charge of the supercharger.

  9. #9
    INDY27's Avatar
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    A cool intake charge decreases the chance of detonation in marine applications, a marine motor is run way harder the a car motor is, it is far easier to make big power in a car motor and have it stay together than it is in a marine motor which which is pushed to the limit for extended periods of time.

  10. #10

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    Quote Originally Posted by Drunken Sailor
    Also, ambient air temperature doesn't really matter either because outlet temperatures of the supercharger are super high.
    That's been exactly my experience too. I've found no difference in power whether the SC is breathing 170 degree engine bay air, or 90 degree fresh outside air. But, just a 10 degree difference in lake water temperature running through the IC makes a big difference in power.

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