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  1. #1

    RXP blow-off valve

    I was considering either investing in one or making a homemade one.

    I did a bit of research and found this.
    11- Run a blow-off valve for the supercharger clutch longevity, it provides no real power gain, but is a big reduction in the abuse that is an actual "good method" of solving a tuogh problem that Rotax had to address when developing this set-up. This keeps the SC shaft from snapping when the pump loads and reloads at high RPM`s and heavy loads.
    So why would Rotax not put a blow-off valve stock?

    Can you actually hear the blow-off valve? I have a few friends with some turbo powered cars (Talon AWD 14psi and another Talon AWD 32psi or something like that. Obviously a big difference between both but even the 14psi you can clearly hear from far. Now stock seadoo runs at 7-9psi I believe? Anyhow I'm just curious. Not really doing it for the sound mostly to make my SC happy and reliable

    Reference from:

    I was looking at this:

    But 200$ seemed a little high to me. And I'm extremely tight on cash lately so thats why I was considering going homemade.

    Anyone have ideas, comments or suggestions feel free to reply!

    BTW: I'll have to take some pics of my homemade sound system that you can still hear at ~50mph. And yes ladies and gentlemen fully waterproof. (how long they will be good for is still unknown :S)

    Only problem is I lost easy access to my glove box but maybe you boys can come up with a few ideas for me on a how-to fix that. lol
    I thought of going dirt-bike style handle bars but I'm not sure I like that look... also thought about tilt steering (GTX Limited Edition style) but that was pretty expensif (400$) and still not sure if that would work... so yeah.


  2. #2
    A BOV is a device that is only used on turbo motors that are plumbed filter, turbo, intercooler, BOV, throttle, motor. When in this order, if the turbo is spinning high RPM (say 160000 RPM) and the throttle is suddenly closed the turbo pressure goes HUGE between the turbo and the closed throttles making the high pressure air to go back thru the turbo. This is real bad on the turbo vains. Your turbo application is not realy prone to this issue as you never shift gears. This is all a hugh problem on the typical DSM application of high boost systems. They can often have a huge volume of traped high pressure air in the intercooler and intake plumbing.

    Hope this helps


  3. #3
    HOSS's Avatar
    Join Date
    Aug 2005
    Kenner, LA
    wastegates are more common on turbo apps, blow off valves on blower apps

  4. #4
    Legend in my own mind Sirhc7897's Avatar
    Join Date
    Aug 2005
    Macclenny, FL.
    My understanding on this is that the BOV is tremendously beneficial for the supercharger but not for the clutch assembly...

    Obviously we're not reading threads about superchargers themselves taking a crap but rather the cluth...That said I think the general consensus is that the added strain on the clutch created by the BOV is a bad thing or at the very least non-beneficial...

    Most of us using the Riva external intercooler are blocking the BOV off...

  5. #5
    So then I guess what you guys are saying is save my money, a BOV on an RXP is useless?


  6. #6
    captain obvious Lurker's Avatar
    Join Date
    Jul 2005
    Visalia, Ca
    please search, this is a topic which has been debated many times by people who know their $hit.

  7. #7
    Save your money and spend it on something else. The BOV does nothing to extend the supercharger clutch. A friend and I thought that was the answer to the dreaded clutch issue on the RXP. That was the only thing holding us back from purchasing the seadoo. We installed them from day one when we got our skis. I lost my clutch 2 times he lost his once so far. Neither are anywhere near 100 hrs.

    If you ride in rough conditions you are going to loose the clutch.

  8. #8
    suck my wake's Avatar
    Join Date
    Apr 2006
    Sugar Grove IL
    A BOV is most beneficial on a turbo application, the turbo is not mechanically connected to the crankshaft in any way, it only spins off of the exhaust gases. The supercharger is mechanically connected to the crank so when the crank slows down so will the supercharger impeller. The turbo will just keep spinning at a million(kidding) rpm's and when you slam the throttle plates shut there is nothing to slow it down except for the suddenly stopped air which may then have an effect on the impeller. A clutch is a WEAR item, no matter what the application it is meant to wear and be replaced at some point. That is just the cold hard facts!!!!

  9. #9
    Any time any sort of pump is moving air, it's doing work and using HP. A BOV when "blowing off" the turbo is working the clutch harder. Try taking your lawn air blower and puting your hand in front of the outlet and watch the RPM go up. Now block the inlet and the RPM goes up. BOV's protect the turbo from reversion. Throttle bodies before the turbo take "work" away from the turbo to hold the RPM up durring sudden drops in throttle position durring full boost.


  10. #10

    "blow off valve" "compressor surge"

    Also found this:

    Good explanation of what bov is for and what compressor surge is

    Function: This device called a blow-off valve (BOV) is really a by-pass valve. Its functions are to prevent or reduce compressor surge and to decrease turbo spool-up time between shifts.

    Compressor Surge:Typically, surge occurs immediately after the throttle plate is closed while the turbocharger is spinning rapidly, such as between shifts or when decelerating. During surge, air pressure increases between the throttle body and the compressor, which reduces the air flow at the compressor. If the air flow falls below a certain point, the compressor wheel (the impeller) looses its "grip" on the air. Consequently, the air in the compressor stops being propelled forward by the impeller and is simply spinning around with the wheel, which is still being rotated by the exhaust gas passing through the turbine section. When this happens, the pressure build-up at the discharge opening forces air back through the impeller causing a reversal of air flow through the compressor. As the back pressure eventually decreases, the impeller again begins to function properly and air flows out of the compressor in the correct direction. This sudden air-flow reversal in the compressor can occur several times and may be heard as a repetitive "WHEw Whew whew" noise if the surge is mild to a loud banging noise when surge is severe. Surge should be prevented at all costs because it not only slows the turbocharger wheels so that they must be spooled back up again but because it can be very damaging to the bushings or bearings and seals in the center section of the turbo.

    So this kind of backs up wastegates argument that the impeller doesn't have to reverse its rotation to allow the gas to flow back in the opposite direction.


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