Exhaust Muffler Design

K

kerf

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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.

http://s747.photobucket.com/albums/xx118/kerf/?action=view&current=GlassPakGenI.jpg

http://s747.photobucket.com/albums/xx118/kerf/?action=view&current=GlassPakGenII.jpg

http://s747.photobucket.com/albums/xx118/kerf/?action=view&current=BaffledExpansionChamber.jpg

http://s747.photobucket.com/albums/xx118/kerf/?action=view&current=NewDesign.jpg
 
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?
 
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.
 
kerf,

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.

steve
 
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.
 
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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!
 

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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 ?

steve
 
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 ?

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.
 

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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.
 
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 ?

steve
 
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