Barry, Great info! I knew a little of that but you put it into context.
My problem is that this is such an oddball machine. '71 Arctic Cat Panther 303 Rotary... They used the 303 from '69 through around '72. This was the dawn of race sleds and the 303 was NOT one of those ;) Theres extremely limited space to put the pipe in and any performance tuning has already been ruined because the exhaust port faces almost straight down. Theres a pipe from it around to the front (maybe 12") which then takes a left turn (the engine is about the same diameter as a 5 gallon bucket but only about 2/3 as tall. If it were a bucket it'd be lying on its side in the sled) and enters the "muffler" which is about the size and shape of a coffee can in the center of one end of the can. At the other end of the can another pipe comes out making another left turn. It goes down about 16" and makes a turn stright down and out. So as you can see this is about the WORST design possible... On a positive note I don't think a rotary engine requires much exhaust gas scavenging since the intake and exhaust ports don't overlap like they do in a piston engine... I like the steel wool idea, I think I'm going to try to end up with a combo approach, baffles and steel wool... -Curt Date: Mon, 18 Jan 2010 08:38:04 -0800 From: "Barry Stark" <barryst...@verizon.net> To: "'Mercedes Discussion List'" <mercedes@okiebenz.com> Subject: Re: [MBZ] OT: Muffler design? Message-ID: <000001ca985c$9c10f290$d432d7...@net> Content-Type: text/plain; charset=us-ascii 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 _______________________________________ 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
