[Nick Weil]

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.

[Eric Alexander]

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.

[Eric Alexander]

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)?

[Nick Weil]

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.

[Eric Alexander]

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.

[Nick Weil]

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.

[David Flori]

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?

[John Savage]

[quote quote=24022]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?[/quote]

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

 

[David Flori]

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

[Steen Carstensen]

[quote quote=25859]Thanks John, I actually built a little microswitch that activates a LED, just so I can see it in actual driving circumstances.[/quote]

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

[Author]

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