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Old 05-08-2004, 12:40 PM
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Exhaust Fabrication

Hey everyone,
I wanna start adding a homemade exhaust sytem to a 3hp 2-stroke engine that'll go on my "old people's scooter". Right now it has a $4 typical lawnmoer muffler which doesnt give out a nice sound. I have spare exhaust tubing of cars lying around and I was wondering how I can make an ehaust setup that will sound better than the current one. I want it to be loud and deep....like a V8 or a Harley. I know this will be hard to achieve but if you have any ideas let me know.
Will it be better to have a pipe going from the engine with a bigger diameter tip at the end, or with a smaller diameter tip at the end. Also a friend told me I should weld a metal plate to the pipe tip (weld it shut) and drill a bunch of holes in it.
Any suggestions and ideas are greatly appreciated.

Mike

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Old 05-09-2004, 08:51 PM
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No one got anything?

Mike
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Old 05-11-2004, 07:44 AM
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Mike

You said it was a 2 stroke. By doing what you are thinking, the motor will be gutless and may even burn up. Two strokes require a certain amount of backpressure. If you look at a snowmobile or a MX bike, you'll notice the pipe expands and then constricts. This is because the sound signal needs to be directed to help pull gas into the cylinder, and then when the piston closes the intake port, partially send fuel that was drawn into the pipe, back into the cylinder to "supercharge" it . Complicated ? Yes. Very. Pipe design all centers around port timing. Very few people have mastered this.


Jeff
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Old 05-11-2004, 04:18 PM
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all of the above AND....

If you close off the pipe then drill holes in it, it is probably going to whistle and be annoying.....
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Old 05-11-2004, 05:05 PM
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So can I keep the stock muffler, weld a pipe to it with a shut end and drill holes in it or will that ruin the engine?

Thanks for the help,

Mike
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Old 05-12-2004, 01:42 AM
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I don't know if it will ruin the engine, but it would still just make the same noise it did, with an annoying whistle....
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Old 05-12-2004, 06:51 AM
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Any changes that are made to the exhaust of a 2 stroke may possibly lead to burning it down as everything is tuned all the way to the end of the muffler/silencer.

If you have any two stroke software for desiging a pipe then knock yourself out and build a few and try them.

Here is a link to a good 2 stroke pipe program.
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Old 05-14-2004, 01:34 PM
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Simply drillings holes in a welded cap on the pipe will not make the whistling sound, you need a dead air space for the whistling to happen.

What you will end up with is a semi-monotone whooshing or rushing sound altered by the amount of pressure built up in the expansion chamber (proper name for the two stroke exhaust systems described above).

Some two stroke engines do not have an expansion chamber exhaust system (weed whackers), but the "muffler" is tuned to perform at the upper rpm range, where the engine does it's designed workload.
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