2 stroke chambered silencer quiet?

Discussion in 'The Garage' started by Chillis, Dec 23, 2011.

  1. Chillis

    Chillis Long timer

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    I have a performance exhaust for my scooter but it's a bit loud. Is it possible to make a silencer that is chambered to cut down on the dB's and stop the need for repacking?
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  2. concours

    concours WFO for 44 years

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    Two stroke exhaust is a science. Much more so than 4 stroke. The "Expansion chamber" portion is critical, size and shape, to scavenge the spent exhaust gasses. Like everything, it's a compromise, low end power, mid range, top end, etc. After all that takes place, the "stinger" or exit pipe must not be restricted (if you want to retain all that scavenging, power making goodness) so a straight through, glass packed silencer is a better choice than none at all. As for a metal, baffled muffler, it'll most likely kill the power gains from the performance pipe... UNLESS it can be be made L A R G E and unrestrictive, usually not feasable on a bike. So, to answer the original Q, not really, if you want quiet, put the stock pipe back on and sell the race pipe. Corking up the (scooter?) race pipe will negate the benefits... and more.
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  3. Chillis

    Chillis Long timer

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    It is a 2 stroke and running the stock restrictive exhaust makes for a boring powerband.

    The stock muffler is considerably quieter though.
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  4. concours

    concours WFO for 44 years

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    Duh, you had it in the title, my dumb. 50cc? bigger? Variator stock? My advice is just get a bigger engine, way cheaper than modding a weenie one. But, I understand the draw to extract just a wee bit more.... :lol3
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  5. Chillis

    Chillis Long timer

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    I may go with a bigger engine down the line but right now I have the performance exhaust. It was quiet when I got it but after 2,000 miles it talks a little bit on the loud side. When people start turning heads, it's too loud. Heads are turning.
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  6. speedracertdi

    speedracertdi Been here awhile

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    Maybe it's time to repack the muffler?
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  7. Chillis

    Chillis Long timer

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    I know but I don't want this to be an every couple of months maintenance.
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  8. concours

    concours WFO for 44 years

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  9. Switchblade315

    Switchblade315 I make people disappear

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    repacking is a once a year thing if you ride it alot. do it right and you might get more.
    #9
  10. CycleDoc59

    CycleDoc59 Wrench Rider

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    Original packing in glass-pac mufflers is often crappy right out of the box,
    so it quickly fails. The solution I've used is fire rope wound tightly around the
    muffler core with any excess packed into leftover space in the housing.
    Fire rope is sold by the foot in wood stove stores, and comes in many
    diameters.

    Last time I used 5/8", tied to the ends of the core with stainless
    wire.....It lasts much longer than loose blanket-type repacking. It took
    30 feet to pack a V&H muffler on a Buell, yours would take much less.
    #10
  11. svejkovat

    svejkovat Been here awhile

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    There are many 2 stroke mufflers that are chambered and without packing. You might even have tossed one out when you added a performance muffler. You could just strap that on the back of your performance pipe, but it may be too restricted at this point (i'm not at all technically competent to guess). Maybe a similar style of aftermarket OEM muffler designed for a larger displacement scooter than yours?
    [​IMG]
    I don't know why more of this type isn't available to top off a performance "expansion" pipe. Guess the performance parts developers have already decided for us that anyone who wants more performance automatically wants that performance to be accompanied by noise to prove to everyone around that it's now faster. Ok, so that's true for 99 percent of us. Personally, I'm with you on this one.

    I'm really a big fan of QUIET. Not quite electric bike quiet, but I just happen to think quiet power is cool. A simple glass packed muffler is just the least expensive method of only barely taming the noise of a small engine. But some two strokes are extremely quiet. It's really not that difficult to come up with a quieter muffler at the end. The muffler above is CAD designed, hemholtz chambered, mass produced high tech. But you can strap on a muffler from a small car as well. I've seen this. It's pretty quiet. It's bulky. It's ugly looking. But at Autozone prices it can be really cheap. Probably not what you had in mind.

    If you look up aftermarket mufflers for utility engines, small generators meant to be used in suburban confines and state camping sites for instance, they often have a series of coned baffles. Kind of like this....
    [​IMG]
    It's interesting that if you google diy silencers for firearms, or even look up cutaway images of commercial silencer design for firearms, there are similarities to the above concept. Firearm silencers really need to be compact and effective. They also can suffer from the same exhaust buildup/contamination over time that 2 stroke engines do. That's gonna be a problem regardless of whether you have fiberglass packing or not. Two stroke residues will build up quickly (condensing on relatively colder metal similar to the way humidity will on a cold window) so that at this colder end of your exhaust, no matter how you construct it, you'll end up needing to 'decarb' it at some point. Maybe you could fiber wrap it to raise the internal operating temp? That would help a bit.
    #11
  12. Chillis

    Chillis Long timer

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    I like this idea and will go in search of it although wood stove stores are few and far between in the desert!

    I like the idea of the gun type noise suppressor. I don't have the where with all to make one and I bet they are expensive

    I tried the stock exhaust but it really flattens the powerband. I will put up with the excess noise until I get this thing repacked.
    #12
  13. CycleDoc59

    CycleDoc59 Wrench Rider

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    Oh...well, just go on line. "fire rope" is better called "stove gasket rope":
    http://www.woodlanddirect.com/Wood-Stove-and-Accessories/Wood-Stove-Repair-Gasket
    #13
  14. Chillis

    Chillis Long timer

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  15. CycleDoc59

    CycleDoc59 Wrench Rider

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    It should be tied to the core at one end, then wound as tightly as possible
    the length of the core, then cut/tied at that end. Any remaining space when
    the core is reinstalled in the shell should be packed with remaining fire rope.
    Or, depending on what size rope is selected, a second layer may be wound
    around the core.

    Pressure pulses and heat quickly destroy original and most replacement
    packings, since it is fairly loose.

    It might be a little tricky with small-core mufflers, but a way to quieten them is to make
    and install turbulators. Here's a link to a picture:
    http://www.fuelefficiencyllc.com/feturb.html This one is shown for a boiler, but
    the principal is the same; without decrease of flow much, they force some of the
    gasses out into the packing. A turbulator can also be made as a spiral. The length
    can be varied to get the effect needed. Staintune sells then for the mufflers they make,
    and calls them "restrictors": http://www.staintune.com.au/faq4.htm

    Contrary to reducing performance, a certain amount of restriction in exhaust systems
    can enhance power curves. As indicated in an earlier post, proper exhaust design is
    critical for 2-stroke engines, and not unimportant for 4 strokes. Noise does not make
    vehicles faster.
    #15
  16. scooteraug02

    scooteraug02 Dog Rancher

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    #16