Back Pressure?

[Cyriak]

I have a Kohler 440-2AX 44HP 2-Stroke in my Hustler, and I am resigning the exhaust system. I am running dual exhaust straight the back, and out of the body. Do these engines need back pressure? And if so , would 2 small inline Mufflers do the trick? I would rather not use Mufflers, but if the 440 has to have back pressure, then its got to have it.

Also, I have got drawing on paper for a Cold Air Intake design. I have heard that there is a performance increase. The current intake is a small ported element housing that almost touches the rear on the hull, stuck down there with all the ridiculous 44HP 2-Stroke heat. Thoughts on this?

Thanks in advance for the help.

Cyriak

[6X6]

Hi:
Two strokes do need a tuned exaust. This provides the right backpressure, and at the right "timing" with eacy cycle to provide better power and efficiency. Your engine will run WORSE with straight pipes than with a muffler tuned for the engine, and just putting any old muffler on it won't really help. I don't know if you have the stock exaust, but if you can find a Tuned pipe from a snowmobile using this engine, (or a similar 2-stroke) you can wring a considerable increase over tuned mufflers. You can custom make the header to suit your needs, as long as you maintain stock diamiter and length.

[Beeman]

Not meaning to take over the post, but I've always wondered about tuned pipes... and if they made variable (length) mechanical ones. The pipes are tuned so that the engine operates at a peak power during x rpm range, but if you could have a variable pipe that changes length you could in theory keep the powerband range over the almost full rpm range of the engine... hmmm

[Cyriak]

I do not have the original Muffler, as it has rusted out. I will say there were many layers/baffles inside the old muffler, obviously meaning it provided alot of back pressure, despite the fact that there is only about 3 feet of actual exhaust pipe, running from a 90% exhaust manifold (not really a manifold). I plan on going with the same diameter exhaust pipe, and roughly the same length. Albeit, 2 pipes instead of one: hopefully. I doubt I could find an original muffler. This will get complicated it seams. I might need to just try it first, and change the design as I go. I will experiment with some chambered mufflers if I have to.

Any thoughts on the cold air intake?

Thanks for the info,
Cyriak

[6X6]

Not meaning to take over the post, but I've always wondered about tuned pipes... and if they made variable (length) mechanical ones. The pipes are tuned so that the engine operates at a peak power during x rpm range, but if you could have a variable pipe that changes length you could in theory keep the powerband range over the almost full rpm range of the engine... hmmm

Never seen them for ATVs AATVs Snowmobiles etc, but they do make a couple for Radio Controlled Cars which use small, alcohol powered 2-stroke engines. They work OK, but not as good as they should in theory, some also have reputations for causing blown motors or making mixture settings VERY touchy. A fixed pipe can be made to have a relatively wide powerband, and this is the style I have preferred, also tends to not be so touchy tuning wise.

I do not have the original Muffler, as it has rusted out. I will say there were many layers/baffles inside the old muffler, obviously meaning it provided alot of back pressure, despite the fact that there is only about 3 feet of actual exhaust pipe, running from a 90% exhaust manifold (not really a manifold). I plan on going with the same diameter exhaust pipe, and roughly the same length. Albeit, 2 pipes instead of one: hopefully. I doubt I could find an original muffler. This will get complicated it seams. I might need to just try it first, and change the design as I go. I will experiment with some chambered mufflers if I have to.

Just be careful. You can cause the engine to run hot if it has no exaust or even just straight pipes. I am trying to dig up a pipe at a snowmobile junkyard. It doesn't have to be for your exact engine, you could use a JLO 440 pipe, CCW, Rotax, Yamaha, etc.... Just as long as it's for an engine of similar displacement, RPM ranges, etc, it will work fine.
OH, I have never seen a Hustler personally, so I can't help with cooling duct ideas.

[micmac]

Cyriak,

You may want to try some vintage snowmobile parts supplier. The mid 70's Ruppp nitro II used this same engine and was a fast sled for its day. I would say a tuned exauhst from one of those machines may do the trick.

[Cyriak]

Thanks for the info guys.