Home Forums Rotax Max RAVE valve – Exhaust Sound?

This topic contains 10 replies, has 5 voices, and was last updated by  Steen Carstensen 6 months ago.

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  • #5137

    Eric Alexander
    Participant

    I have two Rotax Senior motors.  I feel like I have both RAVE valves hitting at 7500 RPM and both have very smooth power transition.  However, one engine’s exhaust note become very brash about 10,000 RPM while the other’s only get brash around 12,000 RPM.  My question is about this brash exhaust note – is this the RAVE valve openning? I’ve read there’s a change in exhaust sound, but I want to be sure what I’m hearing is indeed the valve openning. 

    If this is correct, should  I hear this right at  7500 RPM indicating the valve opens quickly then?  Or does the valve simply begin to open at 7500 RPM and the exhaust note changes gradually as the valve opens slowly over the next few 1000 RPMs?

    Can someone maybe explain what the exhaust note sounds like when the RAVE opens in their own words?

    #5522

    Nick Weil
    Participant

    Try repacking the exhaust matting in the pipe stinger.  Missing matting makes the note much shriller.

     

    An apples to apples comparison can then be done.

    #5670

    Eric Alexander
    Participant

    Thanks Nick.  Always appreciate your responses in the Rotax section.

    Can you maybe describe what to listen for as the valve opens?  The manual states there is an audible difference.

    #8576

    Eric Alexander
    Participant

    I wanted to bump this back up and add to my findings..

    First, once the RAVE valve fully opens the exhaust note does become more aggressive – more edgy sounding.  This sound can vary in volume based on the engines’s state of maintinance: exhaust matting, gaskets, etc.  But the note takes on a slightly harsher or shrill sound once the valve opens.

    But here’s a few more questions for the experts:

    1. Does the valve snap open when the pressure overcomes the spring rate?  Or is it a gradual opening over a few 100/1000 rpms?

    2. Does the Rotax ignition programing actually change the timing at  <7500 rpm to allow the firing of the cylinder to occur as the piston draws even with the closed exhuast valve (on the down stroke)?

    #8878

    Nick Weil
    Participant

    1. Does the valve snap open when the pressure overcomes the spring rate? Or is it a gradual opening over a few 100/1000 rpms?

    A ‘snap’ probably isn’t a proper term or analogy here.  The best example or advice I can give you is to simply run the motor with the PV cover off.  Press the valve in (duplicating spring tension) and then ‘release’ it indicating an overcoming of said spring tension.  This will give you an idea of how quickly it is overcome.  In my opinion, when my engine is running right, it’s almost instantaneous and ‘feels’ good as well as ‘sounds’ different.

    2. Does the Rotax ignition programing actually change the timing at <7500 rpm to allow the firing of the cylinder to occur as the piston draws even with the closed exhuast valve (on the down stroke)?

    During the Florida Winter Tour, I’ve been able to see and use the Coil Tester and I can say that at 7500 RPM’s your coil begins an immediate and progressive advancing of the timing.  Even when bench-testing, you can notice an ‘audible’ note change of the ignition timing.

    #8898

    Eric Alexander
    Participant

    Good info there.  Thanks Nick!

    For the record, there’s alot of vodoo written but the RAVE valve – “set it so many clicks”… etc.  From what little reading I’ve done, the design of the valve comes close enough to the piston that the 7500 rpm is critical to operation.  Open too soon and cylinder compression is lost before the 7500 rpm timing shift.  Open too late and the exhaust restriction reduces HP gains from the higher compression rate after the 7500 rpm timing shift.

    #8952

    Nick Weil
    Participant

    Voodoo would be a very good assessment…  The ‘Clicks’ theory only works if all motors involved in the comparison have the exact same:

    1. Compression
    2. Exhaust back pressure (i.e. matting AND pipe condition)
    3. Spark plug
    4. Jetting
    5. PV spring tension
    6. PV Bellows tension
    7. PV friction coefficient inside the valve slot

    I often enjoy listening to competitors ‘voodoo’ speech regarding power valves.  And watching the other persons reactions to it.

    #24022

    David Flori
    Participant

    Are there any ways to manually adjust the RAVE valves proper opening RPM, or any techniques to find its opening RPM without a logging sensor?

    #25487

    John Savage
    Participant

    Are there any ways to manually adjust the RAVE valves proper opening RPM, or any techniques to find its opening RPM without a logging sensor?

    Buy a new RAVE valve black cap, cut a slot in the side of it and then watch the valve open and close – on the stand with the chain removed and the engine at normal operating temperature

     

    #25859

    David Flori
    Participant

    Thanks John, I actually built a little microswitch that activates a LED, just so I can see it in actual driving circumstances.

    #25877

    Steen Carstensen
    Participant

    Thanks John, I actually built a little microswitch that activates a LED, just so I can see it in actual driving circumstances.

    Please post pictures of  the microswitch and installation, sounds interesting.

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