Kohler 440 twin cylinder 2 stroke

[Don]

As much as I'd like to make the trade, if your machine's going to be for competition, you may want to keep your 6000, John. It's a little lighter, but the big difference is in reliability and strength. The more moving parts you have, the more likely you are to have a failure, especially when the power is being directly transferred through those extra parts.

If it's a racer, you won't need to go backwards anyway.

[hydromike]

Sorry the animation doesn't work correctly on the image. Checkout the home page of AttexATVs.com for the correct working version.

I seriously doubt the 7000 will slow you down vs. the 6000 transmission. I don't think that there's any reduction in the forward or reverse planetary setups. It should be a 1:1 ratio. The weight difference isn't that much in the grand scheme of things. The 6000 and 7000 series both have a 1" shaft, so I doubt one is really much stronger than the other, either. <I was writing this as Don was submitting his message, even though it looks like I'm just being argumentative... I agree that fewer parts are better, and he doesn't need to go backwards...>

A TT is a decent start for a racer. Just keep in mind that the frame may be somewhat fragile compared to later versions. Attex beefed up their frames considerably with the advent of race bred machines like the ST/400/R. Lots of cross-braces, gussets, etc.

To get an idea of what you'd be looking at, check out jpswift1's pictures of his racer. There are some pretty tight clearances in the narrower first generation bodies. It may be a challenge to fit a Kawabunga twin in there, but it can be done.

~m

[gotmuddy]

the animation works for me

[scramblerjohn]

don i still want the reverse tranny,i dont think that going to slow me down a holelot,where i ride i do need reverse,theres alot of woods,i still want to transfer the tranny to the scrambler,there trannys suck,i want to put the tranny in like joes garage,thanks for all the info

[Roger S]

I saw that animation at the attex site, and although I've been a mechanic for a long time, didn't fully understand what an expansion chamber did. Until the last year, refreshing my memory on 4 stroke performance theories. Valve timing, intake and exhaust.. of course it's during valve overlap on a 4 stroke where good things can happen. Low pressure at the exhaust valve and high at the intake. The intake flow can be moving at 70 mph and have several psi, filling the cylinder even though the piston has started moving upward. The exhaust port can have several negative psi helping exacuate the old charge and bringing in the new.

Maybe I shouldn't post in this 2 stroke thread but some will find it interesting.. here's what I read yesterday.

***
Lets take a moment to consider where it all started and where we are now. We took a 5 hp. lawnmower motor that was designed to turn a maximum of 3,600 rpm then bored, stroked, welded, ground, filed, polished, fitted, crammed, invented and generally violated the entire book on common sense and ended up with a remanufactured 10,000 rpm BOMB and all of this was done in the name of fun. Well, of course it is.

We just finished testing an engine with a .174 overbore and 3.000" stroker crank and at 9,000 rpm this is what was happening inside that engine:

1. The valves were opening and closing 150 times per second.
2. The crankshaft rod journal was traveling 79.8 mph in a 3" diameter circle.
3. The piston & rod moved, stopped then changed direction 18,000 times per minute (300 times per second).

Think about this:
The piston is at top dead center (TDC) in a momentary stop position, we've already had combustion, the piston travels down the cylinder 1.3671" reaching a top speed of 84.3 mph, while the crankshaft has rotated 75° and all of this has only taken 1/720th of a second to happen.

Another way to look at it:
The piston and rod start and stop 300 times per second reaching 84.3 mph between each cycle.
***

[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.