Make your own dirtbike exhaust? Why not! - Forums at Modded Mustangs
 
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post #1 of 7 Old April 28th, 2016, 06:47 AM Thread Starter
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Make your own dirtbike exhaust? Why not!

This guy makes his own custom dirt bike pipe and the results are extremely impressive!

Home made YZ250 expansion chamber - Yamaha 2-Stroke - ThumperTalk
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post #2 of 7 Old April 28th, 2016, 07:19 AM
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Geezus that looks like a lot of effort...20 ga. is REALLY thin. Well, whatever makes him happy.

Also I've never really understood how those expansion chamber pipes on 2 strokes work.

---------- Post added at 07:19 AM ---------- Previous post was at 07:19 AM ----------

Geezus that looks like a lot of effort...20 ga. is REALLY thin. Well, whatever makes him happy.

Also I've never really understood how those expansion chamber pipes on 2 strokes work.

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post #3 of 7 Old April 28th, 2016, 09:09 AM Thread Starter
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Haha yea. It looks pretty sick though. I dig the look of the welded segmented pipe. There's a company called Scalvini that makes them for a business.
Scalvini Pipes USA



I'm actually not entirely sure either. I fairly sure they create back pressure though and depending on how the back pressure is funneled creates your power and torque curves. 4 strokes don't need an exhaust to do that. Well they need back pressure, but it's not critical to making any sort of power like it is a 2 stroke.

---------- Post added at 09:09 AM ---------- Previous post was at 09:09 AM ----------

Haha yea. It looks pretty sick though. I dig the look of the welded segmented pipe. There's a company called Scalvini that makes them for a business.
Scalvini Pipes USA



I'm actually not entirely sure either. I fairly sure they create back pressure though and depending on how the back pressure is funneled creates your power and torque curves. 4 strokes don't need an exhaust to do that. Well they need back pressure, but it's not critical to making any sort of power like it is a 2 stroke.
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post #4 of 7 Old April 28th, 2016, 10:37 AM
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Pretty neat!

This is a good explanation of the expansion chamber and how two stroke exhaust works in general https://en.wikipedia.org/wiki/Expansion_chamber
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post #5 of 7 Old April 28th, 2016, 11:33 AM
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Quote:
Originally Posted by 8t6gt View Post
Haha yea. It looks pretty sick though. I dig the look of the welded segmented pipe. There's a company called Scalvini that makes them for a business.
Scalvini Pipes USA



I'm actually not entirely sure either. I fairly sure they create back pressure though and depending on how the back pressure is funneled creates your power and torque curves. 4 strokes don't need an exhaust to do that. Well they need back pressure, but it's not critical to making any sort of power like it is a 2 stroke.

---------- Post added at 09:09 AM ---------- Previous post was at 09:09 AM ----------

Haha yea. It looks pretty sick though. I dig the look of the welded segmented pipe. There's a company called Scalvini that makes them for a business.
Scalvini Pipes USA



I'm actually not entirely sure either. I fairly sure they create back pressure though and depending on how the back pressure is funneled creates your power and torque curves. 4 strokes don't need an exhaust to do that. Well they need back pressure, but it's not critical to making any sort of power like it is a 2 stroke.
You technically never want back pressure in a 4 stroke motor. Back pressure produces inefficiencies in a 4 stroke. I'm not sure where this urban legend came from, but ideally you would have a vacuum in your exhaust to make the most power out of a 4 stroke.

But in a two stroke you want to synchronize the waves or pulses of that pressure with the engine timing, specifically the exhaust cycle. You want to be in the trough of the pressure wave to help evacuated the cylinder. And then you want the crest of the wave to help keep your air/fuel mixture in the cylinder. Tuning the exhaust or dimensions of the chamber, you can control the frequency to whatever RPM band you want the power at.


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post #6 of 7 Old April 28th, 2016, 12:11 PM
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post #7 of 7 Old April 28th, 2016, 04:12 PM
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That's a ton of work but it came out well.
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