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4 stroke dirt bike exhaust

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Here's a question I have (back to the topic at hand, not focusing on people's inability to complete a thought during a post...).

If a straight pipe is best for power, but a silencer is needed, would it be possible/effective/beneficial to create a header/silencer? Let me explain:

Picture an exhaust pipe that is say (I'm picking a number out of the blue) 2" diameter. Inside of that is a perforated 1" (made up number) tube, surrounded by glasspack. Like a standard silencer, but with less packing and the whole length.

Obviously it would be expensive, but what other deterrents would there be? Heat breaking down glasspack?

What about performance? Is there any benefit to having a single-diameter pipe for exhaust?

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The problem is that a four stroke exhaust is tuned through the use of pressure waves, and pretty much any sort of muffler is specifically designed to either absorb or cancel those same waves. Incorporating the muffler into the header is apt to work against you.

Optimally, you would want to create a complete, tuned race exhaust and then dump it into a chamber large enough to pass as the atmosphere, connecting a muffler to the outlet of that. The bulk of such a system would necessarily be prohibitive.

So, the alternative most often used is to use a stepped pipe leading to a straight-through muffler of the "glasspack" type. Any abrupt increase in tube cross section will cause the same sort of pressure reversion that occurs at the end of an open system, though on a smaller scale. These are stacked on one another in series, and together have a similar effect to a straight diameter open pipe. The point at which the pipe finally enters the muffler also acts as an end point.

I believe the design can be improved on by changing to a chambered resonance canceling muffler that could still flow well enough not to impede performance. In order to be effective, though, it could well turn out that the muffler would end up being large, possibly heavy, and most likely somewhat expensive to manufacture.

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That sure makes good sense, and is a bit of what I had been thinking, but you put it into words quite well. Thanks Gray.

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