Kohler 440 twin cylinder 2 stroke

[liflod]

Is there a "power band" felt in your machines with the tuned pipe? My understanding of the "power band" on a race bike is the expansion chamber exhaust working with the reed valves of the engine to give you that power. I know the JLO's don't have reed valves. Do any of the other sled motors use reeds?

[hydromike]

I know that most of you probably already know a lot of this, but I'll throw it out there. You can still benefit considerably from the expansion chamber without the use of the reed valves. The reed valves work to keep as much of the intake charge in the combustion chamber as possible during the piston compression stroke; they work as a "one way street" for the intake charge. Rotary valve engines take the concept a step further, and have a rotating plate timed to the crankshaft that opens and closes the port to each cylinder in time with the compression stroke. Rotax has taken this a step further with some of the "newer" engines with the development of the R.A.V.E valve (Rotax Adjustable Variable Exhaust) which actually uses a sort of exhaust valve to work even harder to close up the cylinder like fort knox. I've talked to people running 670 H.O. Rotax engines in ultralight aircraft (running RAVE valves and conservative exhausts) with horsepower estimates in the mid 120s. All this from a light, reliable, liquid cooled engine.

Expansion chamber design is really a black art that some people just have a knack for. There are a lot of issues to take into account including exhaust gas temp, intake velocity, port area, etc. You're taking advantage of the exhaust "note" traveling at the speed of sound, bouncing off the inside convergent cone of the chamber, and going back at the speed of sound to jam each and every last molecule of volatilized gasoline into the combustion chamber. Ideally, this is timed so that the intake port is already blocked by the upwardly traveling piston. Most of the time, all of this stuff happens in a narrow range of RPM (power band, baby). I have a factory "tuned pipe" on the R, and it's a marked improvement over the stock Attex exhaust, but don't think there's really a noticeable power band though. I'm generally scared between 2000 and 6000 RPM.

If you want to really work hard at chamber design, I suggest the following site. I've read it literally dozens of times, and even went through the math a couple times to figure it all out for each machine. When all was said and done, I decided to leave well enough alone.

I know that Chaparral used reeds in the BW series engines, and I think the Kioritz in the Stobinski Monster runs reeds....


~m

[gotmuddy]

I have a few LT500 quadzilla exhausts laying around, do yall think it would be worth the effort to adapt it to my kohler?

[jpswift1]

ScramblerJohn, the 7000 w/ reverse would add a little bit of extra weight, and it might be some extra gears turning which might possibly give you a little less speed/power, but Im not sure how noticeable it would be. My 7000 transmission in my racer had reverse but I simply removed it and turned it into a straight shaft. It was very easy to do. All you would need to do is add a pillow block with a bearing to support the center of the shaft. Plus this way, you could add an aftermarket torque sensitive clutch to your transmission (which is what I did too) and you will be able to get rid of the factory Attex one which wouldnt work well for a racer application.



Good luck, and Im glad that there is another first generation Attex racer in the works.

[gordk]

Ok.. I will have a look and see if I can offer anything. I am taking a small motors course and am looking at refurbishing an old argo.

[Tremmorkeep]

Guys, i'm going to chime in here if I can. I just acquired this ARGO and wonder if I should rebuild this kholer or just replace it.