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I found this on Wikipedia about using an extra side chamber at the exhaust outlet as a noise canceller:

"The theory of Helmholtz resonators is used in motorcycle and car exhausts to alter the sound of the exhaust note and for differences in power delivery by adding chambers to the exhaust. Exhaust resonators are also used to reduce potentially loud and obnoxious engine noise where the dimensions are calculated so that the waves reflected by the resonator help cancel out certain frequencies of sound in the exhaust."

Now I know what that extra air chamber connecting to the left KIPS exhaust channel is for. I thought it was only for some type of modification of expansion chamber effects but now I see its also for noise cancelling. Since the KDX comes with a special design of expansion chamber for less noise then it makes sense that they'd also use that technique.

Are they not talking about the four-stroke pipes with the extra chamber??

No they are talking about an extra air chamber that has a narrow "neck" connecting it to the exhaust. You are thinking about an exhaust bomb which causes return waves that affect engine respiration similar to a 2 stroke but at a much lesser level.

well that's new to me. Never seen one before. I'd like to see the sellers website to see what they say about it.

That's what I was thinking they meant too, Jason.

My buddy bought a 2016 Husky 250 four stroke and it had one of those chambers on the stock exhaust, I see them more and more on the new bikes.

I have no idea what the purpose of it is though lol

Those are a heimholtz resonator, as someone already mentioned above, they are used to tune/time a reflected pressure wave with the exhaust pulse for increased scavenging or to reduce over scavenging on engines with a lot of valve overlap. Similar in principle to a 2 stroke expansion chamber, but a lot less dramatic in their effect.

Well what is the function of the little "bolt on chamber" on the side of the cylinder on our KDX's?

decreased pressure so it can rev out higher due to lower high rpm compression ??

Tyler, my first post in this thread explains what it's for.

I have seen ones for 2 strokes that come off the stinger.

interesting. do you have a picture?