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Intake & Exhaust The ins and outs - carburetors, manifolds, mufflers, expansion chambers and more to keep your engine running the way you like

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  #1  
Old 10-29-2011, 08:48 PM
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Mike B Mike B is offline
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Default The Silencer

In an effort to make the happy time a bit more quiet, I came up with this.



An Arnold 1/2" B&S muffler with the threaded end cut down and 1/2" copper pipe brazed in. And some elbows and street elbows.

It works! The sound is lower and the low end torque is higher. I can now run slower w/o the annoying "jerkyness". Rolling off the throttle coming to a stop is much smoother. I'm going to add another elbow and a reducer tomorrow and see how that works.

Then I'll paint it all with the high temp grill paint and life will be good.
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Old 10-30-2011, 01:18 PM
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Default Re: The Silencer

Added some more fittings



Another elbow and a reducer with a little copper pipe brazed in the end. I dunno about that reducer size, it wasn't 3/8" as advertised. I cut some 1/2" copper pipe and removed a section so I could squeeze it into the reducer.

Now on to the painting and it goes back on the bike.
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Old 10-30-2011, 02:50 PM
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Default Done

Looks and works great!



I know the exhaust noise is a lot less because the gear noise is now much louder than it used to be -

The extra elbows seem to take a little more noise out and the great low speed performance is still there. Rolling off the throttle is so cool, the bike gets even quieter with no popping or surging, just a smooth decel. Idle is unaffected and smooth. Not to mention I can now roll at idle speed w/o stall. It's a little jerky that slow, but before that was impossible.

It's worth a try guys, less noise and smoother running.

I Like it -
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Old 10-30-2011, 06:26 PM
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Default Re: The Silencer

MikeB,
Looks good.
I too am on a mission to reduce noise on one of my 3 MB's.
I have used the sausage mufflers (large & small) & need to try something else for more reduction. I'm using a pocket bike engine & expansion chamber so noise is much more to begin with. I was thinking of wrapping the pipe in header tape? Think that would do anything?
-Lowracer-
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Old 10-30-2011, 07:51 PM
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Default Re: The Silencer

Dunno. I wouldn't think so.

In order to reduce the noise you need to reduce the pressure pulses coming out of the exhaust. Increase volume, add baffles, add restriction.
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Old 10-31-2011, 02:13 AM
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BarelyAWake BarelyAWake is offline
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Default Re: The Silencer

Header wrap will help reduce exhaust noise somewhat, particularly with the resonant "ping" of a typical expansion chamber's relatively thin walls - think of a V8 with headers vs cast manifolds & the under hood noise.

Not all silencers are dependent on baffle plates, nor is restriction the only way to silence, although it's the easiest way to reduce noise. In fact "loud = power" is a commonplace association that isn't inherently true & I suspect stems mostly from the placebo effect and/or misplaced four stroke exhaust theory. While it is far easier to silence by reducing power through restriction - this does not inherently mean a louder bike is more powerful or that you can't have power and a quiet exhaust.

An example of a quiet, preformance exhaust on a two stroke is a combination of smooth, gentle bends, a matched expansion chamber and header, a glasspack silencer and most importantly - a full length system. Here's the system I've built for my Rollfast, which is both far quieter and more powerful than stock or straight (silencer modified by increasing length/amount of packing);


Last edited by BarelyAWake; 10-31-2011 at 02:23 AM.
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Old 10-31-2011, 04:14 AM
MEASURE TWICE MEASURE TWICE is offline
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Default Re: Done

Quote:
Originally Posted by Mike B View Post
Looks and works great!



I know the exhaust noise is a lot less because the gear noise is now much louder than it used to be -

The extra elbows seem to take a little more noise out and the great low speed performance is still there. Rolling off the throttle is so cool, the bike gets even quieter with no popping or surging, just a smooth decel. Idle is unaffected and smooth. Not to mention I can now roll at idle speed w/o stall. It's a little jerky that slow, but before that was impossible.

It's worth a try guys, less noise and smoother running.

I Like it -
Nice looking with the paint now!

Measure Twice
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Old 10-31-2011, 07:28 AM
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Default Re: The Silencer

BarelyAwake,
Nice pics (going previous in your album).
I may try a different chamber since I have a fairly quiet one on one of my MB's ($40 on eBay). The one I am trying to silence is just that much louder than any other.
Thanks...
-Lowracer-
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  #9  
Old 10-31-2011, 11:10 PM
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Default Re: The Silencer

This thing works good.

Like I said, the gear noise was much louder so I removed the cover and greased the gears.

Then I went for a ride and heard this new "ticking" noise on decel. I smiled when I realized it was intake noise I was hearing, the little suck when the intake port opens and the charge is drawn into the crankcase.

I can tell you that this was the first time I heard that noise when the motor was running.

So yeah, I can say that this thing works so good that you will hear intake noise.

Someday I'll cut the thing and replace that bottom 90 degree elbow with a couple of 45's so it won't be so low to the ground.
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Old 12-28-2012, 12:17 AM
Tacotruck Tacotruck is offline
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Default Re: The Silencer

So what actually lowers the sound
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