Muffler Mod


I did this mod to my stock mufflers to free up some HP and still be eligible for the production class races.  The first time I whacked to throttle, I liked the sound better than my Race Hindle.   It sounds kinda wicked.

So, for those of you with more time than money or those that just like the look of the stock cans, this is for you.

Take all necessary safety precautions. Safety glasses, vices, protective clothing etc. Plan on getting metal shavings everywhere and dress accordingly.

First step is to remove the muffler only from the bike.  One bolt connecting it to the passenger peg mount and three cap nuts holding it to the exhaust pipe.

To remove the three allen cap screws and get the guts out of the muffler, I used a die grinder with a carbide burr bit.

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The next step is to 'gently' grind the area where the screws are welded to the chrome cover on the end of the muffler. I did not have to grind the weld completely off, but once I had most of it off, the screws came loose.

Take care to wrap your pipes in cloth to prevent damage.

In the following pics, you will notice that I did not take any precautions to keep from scratching my mufflers. These were given to me and I just used them as guinnea pigs to see if it would work.

With the chrome cover removed the pipe looks like this. Notice that the end of the muffler is rolled over the prevent the insides from coming out.

Now, take your grinder and as uniformly as possible, start grinding the rolled edge.

Your goal is not to grind off the entire bent over section, but to grind the bend itself. The inner edge that is crimped over will pull out in a big ring.

Watch closely as you grind the edge.  You will notice a faint hairline crack once you ground through the bend.

Once you have completed the grinding and removed the 'ring', use a large pipe stuck up the opposite end of the muffler and use it to pound the packing out.  

Be careful doing this.  It is best if you have a second person lending a hand.  One person to hold the pipe and another to pound the muffler down onto it (kind of like using a post pounder)

Make sure that the 3 cap nuts that held the muffler to the exhaust are removed. The inner packing will not come out if these are on the studs.

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Here is a pic of the packing as it comes out of the muffler. It is a little tough getting it out, but once it is about 1/2 way it gets easier.

Now you will have a completely empty muffler can. Sit it aside and you can begin working on the inner packing.
Remove the outer fiber wrap from the internal metal canister.

Notice that on either end of the canister the ends are somewhat of a cap that has been welded on. You will want to cut the ends off above the weld maintaining the entire cap.

I used a plasma torch to cut the ends off.  You could possibly use a hacksaw, but it would take some time and lot of effort.

You will notice that the exhaust outlet end still maintains the original outlet pipe and has three large relieved holes around it whe compared to what it originally looked like in the first pic with the chrome cap removed. This is only comply with a race guidline.

This is where what you may want to do differs from what I had to do. In the following pics, I use a 2 1/2" exhaust pipe inserted to keep the gasses heading out. If you want to use an inner pipe, you should cut a hole slightly larger than 2 1/2' in the endcap and let the inner pipe seat against the chrome trim ring.

I have not tried running with a can that is completely empty so I cannot give you an evaluation on noise, power, etc.

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In this pic, I am using a 2 1/2" diameter pipe from a muffler shop. I beveled the end that will seat off at the bottom of the muffler to about 45 degrees with a bench grinder. The beveled end will sit in the end of the can pictured in the background.

If you are going to just run the pipe straight to your chrome ring, you should wait until you are almost complete to cut for length.

The next step is to stick the cut off end with the studs into the can, line up the studs with the holes and tap through. Put a small stack of about 5-6 washers on at least one of the studs and then put the cap nut on the end.

Now because I knew I wouldn't be taking the mufflers off of the exhaust I didn't worry about it, but I did find one problem.

Nothing is holding the cap into place inside the can. It is possible that once you get it put together you might drop the can on the studs and drive them inside, but if you are careful and put a nut on it to hold them out until you get them installed it won't hurt anything.

I used some of the packing to help hold the pipe into place.

Next I put on the inner cap, (I put it in ahead of time and took the measurement for my exhaust pipe and cut it to length).

You should push the inner cap into the muffler approx. 1/4" below your freshly cut edge.

Once you have this in place you can use a soft mallet to crimp the edge over. I did not take the time to cut relief slits so when I crimped it, it wrinked a little bit. If I were going to take my time and do it neatly, I would probably cut slits ever 3/4" or so.

After that, just install the chrom cap and you are ready to go.

Total time for the mod will be a few hours if you have the proper tools.

I love the sound it makes now. You can definitely hear it coming and going. It has a wicked racebike sound.

Great thread and pics.

What gains, if any, (a likely loss in back pressure/torque) did you get from all of this effort?

Honestly, with all due respect, it seems like a project most would avoid measuring time involved against overall horsepower gains for the task. :cool:
Can you explain a little more how the inner pipe stays centered up inside the outer canister at the end where the canister bolts up to the header pipe. I'm just not quite picturing that in my head. Is the beveled edge to keep it from moving around?

If I were to take my stock exhaust cans off of my bike and then start the bike up, would I get a good idea of how loud this mod would be? What kind of sound is the final result compared to an aftermarket slip on? Do you get that raspy sound or is it just pure, deep, loud, volume? I was thinking of drilling into the ends of the baffles (did that on a TL1000 I had) but this sounds interesting.
Can you explain a little more how the inner pipe stays centered up inside the outer canister at the end where the canister bolts up to the header pipe.  I'm just not quite picturing that in my head.  Is the beveled edge to keep it from moving around?  
I have the same concern as Justin.

Not trying to dis your mod...

I have done similar things to dirtbikes and had to play this game with an old KZ with a 4 into 1 that kept cracking it's can. How is the inner steel tube anchored against the can in the front. If it is simply tension holdng it in place, the vibrations are going to cause the steel to rub through the aluminum can.

However, I agree, it does make it sound cool/racey.
Great questions guys, no offense taken on any of them.

The beveled end of the pipe makes it seat properly on the exhaust incoming side of the pipe. It does not fit in snug, it only 'seats' it.

You will notice in one of the final pics I wrapped some of the insulation around the inner exhaust pipe to keep it centered inside the can. This kept the pipe from walking off center.

The inner end cap (not the chrome piece) pinched it into place. When I originally slid the inner cap into place, I let it rest gently against the inner pipe. As I crimped the edge over it pinced down onto the inner pipe pretty firmly.

I raced with them all weekend with no problems.

I left the original exhaust outlet because the SCTA Landspeed rules dictate the following

<span style='color:red'>"The exhaust system, looking at the end (down its centerline) shall be unmodified, i.e. the exit diameter of the canister (muffler) cannot be enlarged. This comparison will be made when the bike is asseembled as ready to run. Any performance modifications must be out of view."</span>

This is the 'grey' area of the rules. I had to leave the original exhaust exit pipe in place to meet the rules. I have already had the bike through tech with no problems.

I don't have any dyno sheets, but I am sure this frees up a couple more ponies than just drilling some holes on the inside.

Thanks for the questions, I am open to any ideas on how to do this better.

Ride safe,