The famous KTM exhaust mod - explained.

Here is a stock exhaust. I purchased this set from a fellow in Virginia for a smallish price so I could experiment without putting my bike out of commission. I used a 5mm drill to drill out the rivets and then I used a lot of curse words to pry them apart. It's really hard to get something apart when you have no idea what's inside. But with a bit of patience we got it all apart.

Here's what's inside from the left on the third photo down on the right: End cap. (can be gently pried out from the end once you've drilled out the rivets). Baffle. This combined with the end cap is what makes it so quiet. While it looks like it's wrapped in packing it's really a large perforated metal can held in the center of the canister by a couple of screws - it's a bitch to get out. Muffler and packing. This is like a traditional muffler: a perforated 1.5" core tube with packing wrapped around it. Second end cap. Again sealed with an o-ring and riveted in place. Drill out the rivets and gently pry out.

Supposedly you can remove the end caps and swap sides and the curved parts will point into the perf tube section of the muffler but I didn't try this. I went straight to gutting them and started with grinding down the end cap to break the weld and remove the small tube. Last night I decided to swap the end caps on the Duke for those that were gutted and just see what it sounded like. It's not the full treatment but it certainly is an option and it costs only time and rivets. It's deeper and louder.

Since I don't care for the DOT warning on the cans I thought I'd weld up the small holes that held the center baffles and have the canisters powder coated by Perfection Powder Coating to a nice gloss black. While that's being done I'll fit the perf tube into the end cap and weld it up. For packing I ordered some high performance stuff from FMF that is stuffed loose into the pipe. It's basically 30' of pink string that you wrap and stuff into the cannister. The dyno run will follow as soon as I get Peter to make some time.

Drilling out the stock rivets with a 5mm drill bit.

(L to R) end cap, baffle, muffler, inlet and the canister on top.

In order to get the tube out I decided to grind the end until the weld gave way - this worked well as it allowed me to sneak up on the it with out taking off too much. Basically you grind it back to the lip (arrow).

This is the finished end cap that's been gutted and the 2" perf tube. We're going to weld the tube into the cap, wrap with packing and reassemble and see what it sounds like and what it works like.

Here is the baffle after it's been ground down to the point that it can be pressed out. Now dress the end and remove the burrs.

The other end (opposite the exit) of the perf tube is peened over so that it's snug on the incoming tube seen behind the perf tube. Singles vibrate a lot so you want to reduce as much as possible.

Here I've tack welded the perf tube into the end after test assembling the whole muffler - you real welders can see it's nothing to brag about but I've only been welding for three days now. Those discoloration's and marks will be polished out before the whole thing is packed and reassembled.

I looked at a few options and decided on the FMF 4-stroke long strand packing as it seemed to offer the best quiet to life ratio. It's a really odd bad of 30' pink string...

I tried wrapping the core and then stuffing it in the cannister but it bunched up so I ended up wrapping a few twists then stuffing that down into the cannister. It works out to one bag per muffler.

It's done and it sounds really nice. A nice round, mellow idle with good sound. It's ever so slightly mellower than the end-cap mod as it offers another 6" of packing and a larger tube. Looks and sounds great.