What follows are posts made to the "old" Yamaha forum by DVM.  It's a "how-to" on the first known Yamaha Enduro Sleeper Pipe that many of us bought from DVM and Meis when they were making them for others. 

Many thanks to Don for his contribution of the below posts and photos!

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CT3 Muffler

Update: Ok, I borrowed an air powered cutting wheel from my neighbor and “went to it” cutting the muffler. 


As you can see from the following photos I actually cut much more than I needed to. To access the baffle plates I really only needed to cut out a few inches from the rear. I thought that there was a baffle nearer the front of the muffler. Fortunately, I did not cut the perforated metal holding in the sound baffling material.


Notice the baffle plates. Oh yea, there are ONLY two baffle plates in the muffler not three as I ASSUMED. On the CT muffler there are just two baffle plates in the rear of the muffler and as shown the baffles in my muffler were really disintegrating. 



So, using the idea that MotoVintage had mentioned in a previous post I fabricated a cone to fit in the area where the old baffle plates were located. Actually, the cone shown was a little larger than needed for a perfect fit but being the “old hack” that I am I forced it all together anyway.





Since this is my first attempt at modifying the stock CT3 muffler I temporarily “patched” everything back together just to see how the modified muffler might work. Some high temperature duct tape and some bailing wire did the trick…..”temporarily”. Actually, it was my riding buddy Dave (forum member dtmeis) who suggested this idea.



The preliminary results were OUTSTANDING!!! WOW WEE, my CT3 was performing almost as if I had put my Torque Engineering expansion chamber on the bike!!!! AND the muffler wasn’t that much louder than the stock muffler. So, I took everything apart and fabricated another cone a little smaller that fit into the muffler better. 



Using a MIG welder the cone was welded into the muffler.


Then the muffler casing was welded back together.


Next I put a coat of high temperature black paint to make the muffler look more “normal”. 



THE BOTTOM LINEI gained LOTS of low and midrange power WITHOUT sacrificing top end performance. Next we put the modified muffler on dtmeis’s CT2 which has been ported more for top end power to see what would happen. Again, lots more low and midrange torque without taking away from the top end power! To better illustrate the power attained from this modification our bikes are presently setup with 39/17 gearing (this is our “road” gear, stock is 45/16) and with this high gearing the front wheel lifts off the ground simply my seating back and rolling the throttle. This “cone” idea seems to be a WINNER!! THANKS TO MOTOVINTAGE FOR SUCH A GREAT IDEA!!!

I must say that I’m quite surprised at the improvement that this modification has provided. Also the muffler “looks” original and has the original exhaust silencer (spark arrester) with outlet pipe, so I “guess” that maybe I’m still legal when playing in the forest (the muffler has “US Forestry Approved” stamped on it).

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INFORMATION UPDATE – CONE FABRICATION

Hmmm, did not get much response from this muffler upgrade even though I considered this to be a VERY big performance improvement while keeping the stock look of the enduro!?! Oh well, here is some important information regarding the fabrication of the cone for anyone considering performing this muffler upgrade. When fabricating the cone, you should use the thickest workable sheet metal as possible.  The initial cones that I made were 0.023 inch. It was very easy to work metal this thin into a cone. Unfortunately, time has spoken!!! The thinner metal is prone to stress cracking from all the vibration and sonic shock waves.


I am replacing one of the earlier thinner metal cones with one a cone made of 0.033 inch sheet metal. I used this thickness because it is what I immediately had available. Thicker metal is more difficult to work. Time will tell if this thickness will stand the test of time. I think the original muffler is made of about 0.40” (1 mm) thick metal. I would think sheet metal that is 0.040 to 0.050 inch thick would be ideal for this cone application. After the paint dried the muffler was put back on the bike and I went for a ride.

Mark, your timing with this post couldn't have been better, I think my CT3 will be getting an upgrade once I get it running right.
Thanks DVM and Meis for the design and sharing.

SP35 performing well on my 74DT250A

The cone shaped pressing at the end of the pipe, is very much like what Yamaha used in the TY Mono system.

Factory 240 Fantics, used a system which externally appeared to be an expansion chamber, but internally the front 3/4 of the system, was an absorption silencer, with packing around a perforated core.

The cone shaped outlet part at the rear, was the same as the one used in your modified Yamaha exhaust, essentially the back part of an expansion chamber.

Fantic went on to use the factory type exhaust on their next model production bike, and carried on using the same design exhausts till they folded in the early 90s.

I would think that mod would work very well on any system, which has those punched hole baffle plates, which do reduce noise, but dont do much to help with good running.