Any manufacturers ever mess with 2 strokes with exhaust valves?

[CDave]

Kinda like a Dietroit Diesel.

[merklebob]

last on i saw was a 35hp oliver outboard from 1959. may have been inlet valves thru. this was a very strong motor for its day but hard to find part for.

[Blizz]

All of the snowmobile mans are using exhaust valves and have been doing so for quite awhile some of the small pro racing outboards have them also.

[BarryStrawn]

I've never seen or heard of a production outboard with an exhaust "power valve" as is commonly used to vary the height of the exhaust port.

The Detroit Diesel two stroke uses a camshaft and poppet valves in the head. Cycling rate would be a problem on a high speed two stroke. Even a 7,000 rpm two stroke would require a valvetrain equivalent to a 14,000 rpm four stroke. $$$$

[pyro]

I thought the ones on sleds were for varying the amount of exhaust backpressure to suit the RPM range.

So it's actually variable port timing?

[BarryStrawn]

Several variations. Quick search found these links.

http://www.offroadhaven.com/powervalve.htm

http://www.poetonaptec.co.uk/technica/mpcxvalv.htm

[Blizz]

yes the ones on sleds are for varying backpressure to help it keep on or get back on the pipe faster, it also helps torque, kinda like a slider that the mod outboard guys use.

[sosmerc]

...here's something new from STIHL

http://www.stihlusa.com/whatsnew/news_fourmix.html

[Scale Performance]

the e-tec 70 hp 2 cyl will more then likely have a exhaust valve.