Exhaust Power Valves for 2 cycle outboards?

Chris1956

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Some PWC engines have them, some motorcycles have them. Were they ever incorporated into an outboard?
 

Sea Rider

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Are power valves same as hydraulic ones as found in many motors specially cars. If that's what you're asking for probably found on very large HP-OB's...

Happy Boating
 

Chris1956

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Power Valves found on 2 cycle motors vary the size of the exhaust port, depending on RPM. Low RPM causes the valves to close somewhat changing the exhaust scavenging characteristics.

Rotax engines on Sea Doo PWCs have exhaust pressure operated ones. Other PWCs have mechanically driven ones. Some motor cycles (Kawasaki?) have them, and they are controlled by a mechanical RPM mechanism.
 

Chris1956

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The PWC applications are water cooled. The motorcycle looked to be air cooled.
 

Baylinerchuck

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Those are most prevelant on snowmobiles.

Definitely. Most if not all larger cc 2 stroke snowmobile engines have the valves on the exhaust ports. If the diaphragm gets torn or the valve gets carbined up, there is a noticeable loss of power.
 

Chris1956

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Fazt, I read some advertisements for e-TEC. They claimed to have a tuned exhaust for their V6 models for full throttle operation. They also claimed to have a valve in the exhaust system to vary the size of the turned exhaust chamber, for another distinct power band.

Any idea if they worked as well as advertised?
 

He rik

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On motorcyckel there are big difference in power if the valve dont work but they are very small and max. effect at high rev so its hard to get both bottom and topeffect.

Outboard with big volume and max effect at lower rev dont benifit in the same way from exhaust-valves, maybe thats why there arnt so many of them, another moving part that can fail and not much to gain...
 

Faztbullet

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The BRP G2 3 cylinder 150HP uses these RAVE valves to make it's HP and they make a HUGE gain in power and torque..
 

flyingscott

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Exhaust valves make a big difference on 2 strks. They allow the port height to change allowing for.better bottom end power and maximizing .top end.
 

He rik

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You can always tune for max effect on any given two-stroke w/wo valve but with a valve you can get both bottom and topeffect, but with big volume and tuned for maxeffect a bit lower you loose some top but get a good bottom anyway.

To benifit from exhaustvalves you might have to build a smaller engine and tune for topeffect at a higer rev. and use the port to get the bottom, or rebuild the big engine to allow it to rev higher witout "expolde" to get more top.

You get a broader register from moving the top higher witout loosing the bottom or more bottom witout changing the top.

Question is if we need it on a boat, fueleconomy perhaps but 150hp is 150hp if you use it...
 

Chris1956

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Fazt, Is that G2 a Rotax engine? RAVE valves are usually associated with them.
 

Faztbullet

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82rude

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Had a late 90,s mxz 670 ho that had the rave valves and let me tell you that sled was a screamer.Realiable as heck and know as an 800 killer!Way under reported in hp.Claimed 125hp actual dynode at 140.I put a reverse kit in it and 196 studs for grabbing power.She could easily heap up with my buddies big Yamaha 4 strokes.It was about double mpg vs my Yamaha 600 vmax which was a damn gas hog.
 

QBhoy

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Apart from the issues they can cause in some engines..like carboning up or even dripping into the piston...great things...haha.
 

flyingscott

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apart from the issues they can cause in some engines..like carboning up or even dripping into the piston...great things...haha.

hmmmmm Sounds like the same problem DI cars are having with valves carboning up.I do not see it being as big an issue in the E-tec motors.
 
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WIMUSKY

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Had a late 90,s mxz 670 ho that had the rave valves and let me tell you that sled was a screamer.Realiable as heck and know as an 800 killer!Way under reported in hp.Claimed 125hp actual dynode at 140.I put a reverse kit in it and 196 studs for grabbing power.She could easily heap up with my buddies big Yamaha 4 strokes.It was about double mpg vs my Yamaha 600 vmax which was a damn gas hog.

Interesting. I'm looking for an 06, 07 or so MXZ SDI 600 'Gade..... Sold my RX1 ton, that's what the wife rode...
 
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