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Old 12-23-2011, 09:05 PM   #16
Airhead Wrangler
Adios Mexico
 
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Joined: Mar 2008
Location: Back in Seattle, FINALLY
Oddometer: 6,387
I fired the core out the back of a jawa 350 twin. It made one unholy smokey racket. I walked back and picked it up and jammed it back into the tube and rigged it with bailing wire. It stayed together long enough for me to lunch the transmission a couple weeks later. I ended up selling the bike for parts at a livestock bazar in eastern Kyrgyzstan. True story.
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R80ST Gets The HPN Treatment
Seattle to TDF on an airhead

Current rides: HPN #834, '93 R100GSPD "red rocket", '73 R75/5 Toaster mongrel, '80 Ducati Pantah 500SL, '92 DR350, '67 Honda SS50, '80 Honda Chaly.
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Old 12-23-2011, 10:57 PM   #17
dorkpunch
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Joined: Aug 2006
Location: Blackfoot, ID
Oddometer: 5,069
I had a Honda Trail 70 that had exactly 2 inches of exhaust pipe. It ran that way for years, and years, and years, and , well you get the picture. Always heard that running an engine like that would ruin the engine because the exhaust valve would be cooler than its supposed to be. I eventually tied a muffler on to it (literally) and its still going strong...

Pic from after the muffler instal- maybe 10 years after the original fell of.

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Old 12-24-2011, 06:23 AM   #18
Airhead Wrangler
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Location: Back in Seattle, FINALLY
Oddometer: 6,387
I'd say that half of all trail 70s still running today are used almost exclusively for popping wheelies in one's own yard and other assorted hooliganery.

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R80ST Gets The HPN Treatment
Seattle to TDF on an airhead

Current rides: HPN #834, '93 R100GSPD "red rocket", '73 R75/5 Toaster mongrel, '80 Ducati Pantah 500SL, '92 DR350, '67 Honda SS50, '80 Honda Chaly.
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Old 12-24-2011, 07:51 AM   #19
dorkpunch
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Location: Blackfoot, ID
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It was used a lot for that, fer sure.

Before it was mine, it belonged to my brothers friend, who rode it from town 2 miles out to the dirtbike track, then around the track. He also put TWO other people on it with him, then the 3 of them would take turns riding around the track.
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Old 12-24-2011, 09:07 AM   #20
baldwithglasses OP
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Joined: Jul 2007
Location: East Atlanta Village, Atlanta, Georgia
Oddometer: 795
I found some instruction here:

http://www.practicalmachinist.com/vb...design-225238/
"If you want to make a muffler and have access to some fairly basic sheet metal working tools, the job is easy. Take some 12ga or 14 ga stock and roll a cylinder that is something on the order of 6" long by 3" - 4" in diameter. Bigger is better. Using a hole saw of suitable diameter, cut a couple of ends, using slightly heavier stock, maybe 10 ga. Cut a rectangular piece of flat stock so that it will bisect the cylinder into two equally sized half-cylinders. Using a small drill, about 1/4" or less, drill a series of holes in one half of the rectangle so that you have a solid square portion and a swiss cheese square portion. (I' m trying to be illustrative here.) The combined area of the holes should approximate the cross section of the NPT pipe inlet. Now, using another hole saw, cut suitably sized holes in one end round to accommodate your desired pipe fittings. These holes should be offset so that when assembled the inlet hole will be on one side of the rectangular divider and the outlet will be on another. It may be a good idea to extend the inlet pipe into the muffler a bit with a bracket to the body for strength. The swiss cheese portion of the divider should be away from the inlet and outlet.

Weld everything together and you are ready to go. Remember, muffler's volume, the quieter the result. Also, the more convolutions you add internally, the quieter the result. Circular drilled baffles or a series of alternating three quarter baffles will work at least as well as what I described and make it easy to have the inlet on one end and the outlet on the other but may be harder to assemble. If the volume of the muffler is sufficient, it may make sense to downsize the outlet pipe by one size.

The non-technical reason engine exhaust is noisy is because a volume of compressed air is released rapidly, creating a big POP, sort of like popping a balloon. What you want to do is to break that percussive emission into a steady, smooth flow of air. Mufflers work primarily by having that force front of air bump into things until it loses some of its energy and flows out smoothly.

You can calculate some dimensions to make an expansion chamber muffler if you really have nothing to do. The volume of the muffler should be at least the volume of the engine's displacement, and the outlet pipe diameter should be such that one volume of air will flow through the pipe at your desired back pressure in the time it takes the engine running at full speed to complete one cycle (two revolutions of the crank for a four cycle engine). I'm sure there is much more to it than this but I just want to convey a general idea. "
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Old 12-24-2011, 04:54 PM   #21
Quasi1960
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Location: Darkest Gloucestershire
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I had a silencer fall off my Bonneville. I did go back for it, but the car behind had run it over. Bastard!
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