Curt - Manfred is correct. The downside of not using a properly designed exhaust system is that you may end up with a destructively lean mixture at full throttle, or you may just have reduced power. While the reduced power is likely not a big thing, the excessively lean condition can be. With whatever system you end up with be sure to take a spark plug reading after a short full power run to determine if the mixture is within range. If it is just a bit lean you can likely either adjust the high speed needle valve or install a bigger main jet depending on the design of the carburetor. If it "blubbers" it may be too rich and the appropriate adjustments can be performed to correct that instance as well. The best system for a 2 stroke is what is called an expansion chamber. It consists of a divergent pipe, like a megaphone, and then a convergent pipe, just the opposite, followed by a small length of a small dia. straight pipe. The length and diameters of each of these sections are somewhat critical but the cones can be ovaled a bit and pipes curved usually without too much loss of efficiency. The unfortunate part of these expansion chambers if they can be quite noisy. If you have ever witnessed a 2 stroke racing motorcycle you will know what I mean. The factory muffler is likely designed to try and emulate the characteristics of the expansion chamber in a very small package. Very hard to do without some fluid flow type engineers and a dynamometer. Your best bet may just be to try and make a unit that is quiet as possible, take plug reading and adjust the mixture, and live with any power loss. The secret to making a quiet muffler is to rob the sound energy from the exhaust pulse. This is done by trying to bounce the sound off as many surfaces as possible. Often a "gun" type silencer will do pretty well which is basically a pipe. With a bunch of holes drilled in it, surrounded by a chamber stuffed with sound deadening material like steel wool or rolled fiberglass. If you use this design the deadening material will burn out over time and will need to be replenished. A more longer life method may be a series of chambers with internal baffles that have holes with the edges deformed like a simple cheese grater. You may have seen this used in automotive mufflers. By the way, have you looked to see if there is a performance aftermarket exhaust system for your machine? There may one available that is not too noisy. Ebay? If you would like to learn more about 2 stroke expansion chambers and their theory I just Googled "two stroke cycle expansion chamber design" and got a number of interesting hits including some possible chamber design parameter computer programs. Wikipedia had an excellent animated discussion on how expansion chambers work.
http://en.wikipedia.org/wiki/Expansion_chamber I hope some of this helps out. Barry > > -----Original Message----- > > From: mercedes-boun...@okiebenz.com > > [mailto:mercedes-boun...@okiebenz.com]on Behalf Of MG > > Sent: Monday, January 18, 2010 6:44 AM > > To: Mercedes Discussion List > > Subject: Re: [MBZ] OT: Muffler design? > > > > > > Curt I think the design of mufflers is a bit different between > > two and four stroke. The two stroke muffler is usually an > > integral part of the power band tuning of the motor, much more so > > than with a four stroke. Try cutting open the original muffler > > and see if any of the pipe and baffling are still in there to see > > if you might be able to copy it in the new muffler. The closer > > you can get to the original the better. Even the distance between > > the head and the muffler is part of the tuning. > > > > Manfred > > > > > > > > Date: Sun, 17 Jan 2010 19:37:07 -0800 (PST) > > From: Curt Raymond <curtlud...@yahoo.com> > > > > Anybody know anything about muffler design? I've got an old > > snowmobile that the muffler is NLA and a strange enough design > > that nothing else will work right. > > I bought a muffler from a Cub Cadet tractor and its okay but > > still too loud. It looks like that "muffler" is just a can with a > > tube that has holes punched all around it inside. > > > > I *think* quiet mufflers generally have some kind of fiberglass > > packing inside. I've got to cut this muffler anyway since its too > > long, I was thinking that since I had to have it open I'd stuff > > some fiberglass in (either the pink stuff or some mat) around the > > outside and see if that helped any. I don't think it could make > > it any worse... > > > > I've also thought about welding in more baffles but theres not > > that much space, its about the size of a coffee can. > > > > -Curt > > > > _______________________________________ > > http://www.okiebenz.com > > For new and used parts go to www.okiebenz.com > > To search list archives http://www.okiebenz.com/archive/ > > > > To Unsubscribe or change delivery options go to: > > http://okiebenz.com/mailman/listinfo/mercedes_okiebenz.com > > _______________________________________ http://www.okiebenz.com For new and used parts go to www.okiebenz.com To search list archives http://www.okiebenz.com/archive/ To Unsubscribe or change delivery options go to: http://okiebenz.com/mailman/listinfo/mercedes_okiebenz.com
