Exhaust Muffler Design

Discussion in '2-Stroke Engines' started by kerf, Aug 2, 2009.

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  1. kerf

    kerf Guest

    As some of you know, I'm running a R460 through a Staton chain drive. Performance of the 460 is great but it's very loud and I've been using secondary silencers to quieten it down. I've built several, each one an improvement over the previous one, the goal to get the noise down to the level of my wifes TLE43. My first attempts were straight through glass packs, culminating in my current baffled expansion chamber design. This works the best but I would like to combine the glass pack with the expansion chamber into a Gen IV Muffler.

    The new design would dispense with the silicone exhaust tubing coupler as these burn through after only a couple hundred miles. The inlet of the new design would be sized to be a tight slip fit over the outlet stub on the 460's factory muffler. The outer jacket on the new muffler would be made from 2 1/2" exhaust pipe with all parts being steel and wire welded. I'm currently unable to post pictures so I've been forced to use Photobucket. I've posted links to photos of my previous designs as well as a drawing for the new design, comments and critique would be appreciated.





  2. Happy Valley

    Happy Valley Active Member

    I look forward to your impressions when you try the new design Kerf. I've been following your results and you documenting your efforts over the past months and have appreciated your pursuit on this.

    About a year ago I got my hands on a new Mitsubishi T200 40cc engine. This doesn't have the same stratified version as the TLE43, more just a straight through design and very peaky. I didn't get the engine from Dave Staton but he mentioned it was the engine he had one used to go the fastest he's been on a MB clocked at a little over 47mph on a closed track.
    It's a real screamer but very loud and ever since I got it I been trying to quiet it down. My efforts so far have been less than satisfactory.
    I can it it into a reasonable decibel range but at the expense of serious power loss.
    So, I'd spent a fair amount of time doing my amateur exhaust and muffler science reading. 2 strokes present their own exhaust science challenges of course and I'm quickly over my head left plodding along with trial and error, mostly error.

    So far I've left the stock muffler on and added to it. My thoughts now question if I would be ahead by designing something that bolts right to the exhaust port eliminating the stock muffler as a way of muffling noise but not losing as much power?
  3. kerf

    kerf Guest

    I've has the same thoughts but not being into tuned expansion chamber construction I thought that the factory muffler might act as a buffer to my handiwork. So far I've lost a little over 10K but that's not my normal driving range. The current muffler actually seemed to help the torque in the 7 - 8K range. I'm running 18.75 /1 gearing, I could probably pick up top end by dropping my ratio to 20 /1, allowing the engine to wind tighter but this would increase my noise level at my 30 - 35 MPH cruise speed.

    Please remember, kerf's just an old fart.
  4. DetonatorTuning

    DetonatorTuning Active Member


    my experience with the Dominator expansion chamber are that the pipe starts out pretty reasonable in sound from idle to 20mph, it starts to "come on"to it's power enhancement just under 25mph. it's still reasonable at 33mph but by 35mph it's singing pretty well, from there up it's could be said to be "wailing".

    is the new design to be the same dia. as the last version ?

    since you are using a foward and aft chamber along with an independant perforated core i'd suggest going as large as you can stand, to accomodate a nice thick loosely packed 'glass matting (thick and loose is quieter than the same depth tightly packed) and as much volume as possible in the aft chamber between the matting and the exit core.

    your foward chamber will provide you with the resonant reflex wave you want for the midrange and a large volume chamber behind it will allow the exhaust to expand further while being contained long enough to bounce around and dissapate much of it's sound levels.

    good luck, i'm sure the workmanship will be topnotch as usual.

  5. kerf

    kerf Guest

    Thanks, the new design will be a little smaller in dia. than the current one but longer. Total volume should be a wash, with more room for fiberglass than anything to date. I wish there was a tuned pipe that ran under the engine, similar to my current routing. Thought about modifying a Dom but after some of your experiences, I better stay hands off. Those things don't seem to like shade tree tinkering, I'm working in a shop but shade tree is my middle name.

    By the way, replaced the cheap stamped prototype track sprockets, on the two speed, with Shimano Dura Ace machined cogs and swapped the larger sprocket to the outside of the adapter. That puts the dérailleur in the "home" position when in high gear, where I stay 90% of the time. The shifts are now as smooth and seamless as the right side dérailleur.:tt1::tt1::tt1:
    Last edited by a moderator: Dec 16, 2015
  6. kerf

    kerf Guest

    The new muffler is finished and installed, so far so good. I changed the design at the last minute to a forward expansion chamber with an aft straight through glass pack. There were two objectives to the project: 1. Quite down this screaming chain saw that is the GP460. 2. Eliminate the silicone connector tube between the primary and secondary muffler.

    Welding was a bit of an issue, needed argon but had none, started with .030 flux core but switched to .025 solid with CO2. I brazed the end cap in because burn through was an issue welding on the edge of the 16 ga. cap. After a little cutting, welding, grinding and drilling, I came away with something that looked remotely similar to my drawing. The slip fit of the secondary inlet to the primary outlet was pretty close, about .006", I sealed the joint with Rutland Black Hi-Temp Stove & Gasket Cement, supposed to handle 2000 degrees F. As I wanted durability, I wrapped the baffle tube with fiberglass cloth before applying the glass packing. Hope the cloth keeps the batting from blowing out.

    About 6:00 PM yesterday, I went for the first test drive, performance was good but I was disappointed with noise reduction. Woke up at 4:00 this morning, realizing the drone I was hearing was intake noise. Quickly built an intake baffle from one of the wife's Tupperware containers (it gave its life for the cause) and hit the streets at 6:00. Wife was in the den watching the news when I passed the house at 30 mph and she never heard me. Later while she was in the driveway, I made a couple of passes down the street and she said it sounded just like her TLE43.

    Sweet success!

    Attached Files:

    Last edited by a moderator: Dec 15, 2015
  7. DetonatorTuning

    DetonatorTuning Active Member

    nice work as usual.

    only concern being the total area of the holes in the intake baffle, do they equal or exceed the area of the holes in the air cleaner cover ?

  8. kerf

    kerf Guest

    I don't know, that was predawn R&D.

    Since I posted I've built the actual silencer. The total area of the 8 holes is 4.35 times the area of the venturi. Hope I'm ok, know tomorrow. In any event I'm disrupting air flow (only way to silence) so there will be a price, as long as its in penny's, I'll pay.

    Attached Files:

  9. Happy Valley

    Happy Valley Active Member

    Nice work Kerf and thanks for the detailed update. Instructive when you dampen the exhaust port the intake port noise becomes prevalent, I'll keep that in mind with future experiments.
  10. DetonatorTuning

    DetonatorTuning Active Member

    do you have padding between the new silencer cover and the original air cleaner like the tupperware unit ?

    i can't see where going thru that much area is going to disrupt the air flow to any noticable amount.

    just what is that cannister ?

  11. kerf

    kerf Guest

    The carb side of the silencer is sealed with a piece of 5/8" round foam caulk backing. This effectively seals the silencer to reduce noise from being directed toward the rider. I went to Wally World looking for something to use for my silencer, finally found a three piece canister set, regular price $6.95, on clearance for $2.00.

    There is about a 1 1/2" space between the end of the air filter cover and the canister. I tapped the air filter screw hole with a 1/4 x 20 tap and used a short piece of threaded rod with nuts to hold the parts in place.

    I did a 20 mile run this morning, if anything it's running better, go figure. On the down side, I'm suddenly very much aware of my chain.
  12. DetonatorTuning

    DetonatorTuning Active Member


    in persueing the sound issue you may have dovetailed over to another that you had previously been concerned about.

    at times you have mentioned that under low speed ,high load conditions you have strong inlet back pulsing from the carb that soaks the filter and causes rich running.

    the new chamber MAY be adding just enough extra resistance to cancel some or all o fthe intake reversion pulse.

    keep track of your filter and let us know if this is true. pretty awesome if it is.

    also keep a close eye on your plug, you may suddenly move leaner as a result.

  13. kerf

    kerf Guest

    Thanks, I'll do that.
  14. DetonatorTuning

    DetonatorTuning Active Member

    any changes at the plug or mileage to report ?

  15. kerf

    kerf Guest

    New Direction

    Many of you are aware of my battles with the R460 and the associated noise this little engine produces. I've tried many different muffler designs and my last one has proved the most effective. It also brought to light another noise source, intake noise. My solution was to put a silencer over the air filter to gain a little edge on the noise, the muffler and silencer are documented in this thread. Not totally satisfied (who would have thought) with my results, I added some fiberglass air filter material between the stock air filter and the end of my silencer. This helped a great deal but decreased air flow as evidenced by an over rich condition, which I corrected by adjusting the carb. Again not content, I began research into another method method to cut intake noise.

    I began searching intake noise and found an interesting article about a guy with a Tomos 55 moped. He had installed a HP air filter and gotten pulled over for illegal muffler, which I recount to illustrate the significance of intake noise. What I was actually after was information on the Helmholtz Resonator and how I could employ it to help my problem. The two methods that I found to correct this issue were pre air filtration silencing and post air filtration silencing, the Helmholtz Resonator or as it's more commonly known an air box. Air boxes are widely used on engines today, especially in the automotive industry and I thought this might be the answer.

    During my searches, I found an intake silencer for a Rotax ultra lite engine (IMG 1), this seemed pretty simple to me, an air box between the filter and carb with the filter at 90 degrees to the carb bore. Working on this principle, I began looking for a suitable box and settled on one of my old friends, a 4 x 4 x 2 inch electrical box from Home Depot. This plastic box has no ports or openings (drill your own) and has a "marine" rating, due I guess to the O ring sealed lid. After determining how I wanted to mount and brace the air box, I did a little drilling and painting (Krylon Fusion) and put it together. I have photos of the mounted box (IMG 2), the brace (IMG 3) and the assembled unit (IMG 4 & 5).

    My first test ride was amazing, first off I had to lean the carb back out and for the first time I realized just how effective my muffler is. This has reduced my engine noise by at least 50%, absolutely unbelievable!

    Attached Files:

  16. happycheapskate

    happycheapskate Active Member

    I'm running a lawnmower box muffler because I don't care about the noise (it wakes up drivers!).
    I think if I cared about noise I would look for some kind of large chamber with baffles in it to change the noise to a deep echoing sound.

    Has anybody tried running their exhaust through a truck heater core or oil cooler? That would change the direction of the exhaust many times, cool the exhaust (which might reduce sound wave volume at exit), and would provide variable back pressure (a valve like on gas or compressed air pipes might even be incorporated)
  17. professor

    professor Active Member

    Today I learned what happens when you take a muffler off a 98cc two stroke.
    I drained the gas after pulling the engine (flipped it upside down and shook it around). Then decided to pull start it as it sat on a chair to get all the gas out before putting it away.
    At the idle stop, the engine raced at probably 3000rpm for a good couple of minutes ( with me hanging on to it real good). I have to think the 3hp cigar muffler (and piping) was a big hp killer.
  18. happycheapskate

    happycheapskate Active Member

    Thats just silly to fire or start any kind of engine without it mounted to something.
  19. happycheapskate

    happycheapskate Active Member

    Thats nice but seriously complicated. What is the metal round part that is on the outside of the home depot box, before the air filter (nice filter!)

    Why not just use a 4x2 box with a oiled foam filter in it, with 25 cent size holes on the outside, like a briggs and stratton lawn mower filter box. The foam filter will absorb fuel that blows out of the intake on downshift/decelleration and should cancel a lot of intake noise.
  20. kerf

    kerf Guest

    Actually it's incredibly simple. The R460 is a high performance engine and to that end, is provided with a high flow gauze air filter similar to a K&N. The trick is to reduce the intake noise while not substantially increasing air restriction. The Rotax unit, I modeled mine after, list a 2% reduction in power, in my case that would be almost .1 horse power. So far I can't tell any difference in performance but I've only been up to about 8400 rpm (35 mph), but throttle response feels good. Having a solid surface directly across from the throttle bore must reflect some of the sound waves back toward the source, whatever, it works.

    The round metal object on the side if the air box is a velocity stack.