Custom muffler, worth the read..... the past 4 years, I've trolled this magnificent website regularly, and have applied the knowledge to everything from Buells to watercraft, harleys, hondas, scooters and more! 


That said, thanks for reading my first post!!




2001 WR 426. Particular bike is new to me, however the breed is not. I've had my YZ 426 for 6 years. took about 3 years to find the right WR for the right price. In the process of getting it plated now, so its intent is a street machine.


I don't see, or have missed, custom exhausts. Mufflers in particular. I say this because I cant help but notice upon inspection, or repacking mufflers, how much they resemble a glass pack muffler. No not JUST because its actually packed with glass "fiber", but in its design as well. 


I also can't help but notice that the silencer insert, or spark stopper thingy, looks/acts alot like a "baffle" you might find stuffed in the tail pipe of harley that someone tried to quiet down with out dropping 600 bucks for new exhaust.


Glass packs are dirt cheap, come in numerous lenghts, with a decent choice for inlet/outlet diameters. And typically have an overall diameter of 3-3 1/2 inches. Oh and they're packed with glass fiber!


The inserts can be had in diameters to match the glass pack outlet, and are held in via set screw, trust me, it holds. The key to the insert is that they come in various lengths as well, and can very easily be cut! So now we have the ability to tune the muffler. 


I've done just this on an old harley shovelhead bobber, ran great, trimming the baffle seemed to do more for sound then anything. I got better results from changing the distance of the glass pack in relation to the exhaust valve. But the point is it worked. That motor was a 1200 CC motor that rarely made it to 5000 RPM.


Anyone see an issue with running something like this on the smaller, higher revving motor in my WR? It seems to be the same concept as a factory muffler, just in a different package, so to say. 




Sounds like you’ve done some of the same experimenting that I have.   The mufflers you mention resemble glass packs because they are glass packs.  I haven’t seen any aftermarket mufflers that are a chamber design like the stock pipe.   I have an FMF Q4 on my 450 and got tired of repacking it.  It sounded great when I got it but after only few hours it was louder, this I confirmed with a   decibel meter.  You had to repack it just right, too loose or too tight and it was louder.  It’s baffle consists of 2 layers of perf pipe with a screen in the middle, the assembly is wrapped with fiber. 


So I got some pert metal sheet and made my own baffle, trying several  designs until I got one that worked, was low restriction, sounded right and was not dependent on packing.  It’s been in there for most of last season and hasn’t changed.  It’s a hybrid chamber type with a screen in the middle.  


In my work on street bikes I’ve found the same things you have.  The length and diameter of the header pipe, also the length and diameter of the glass pack.  And with any exhaust system, the larger you can make a muffler, the quieter and lower restriction you can make it.  If the muffler was the size of a barrel the bike would be almost silent.  


I’d say try your experiment with the glass packs you’ve found and let us know how it works.  

I bought a race series Big Gun muffler years back dirt cheap for a KLR 650. Guy selling it took it off as he said it was to loud. THAT was an understatement. It was deafening!

It is a typical dirt bike muffler with a perforated pipe running down the center wrapped by glass in a big aluminum can. It DID have a screen bolted

across the back to make it a USFS approved spark arrestor type muffler.

I pulled the back cap which basically had about an inch and half diameter hole (the same size as the perforated core in the muffler) and machined three round plates each with different hole sizes and patterns in them to try and quiet it down. I managed to keep the screen as well so I did not loose the Forest Service approved spark arrestor. These plates also had bolt holes matching the screen and end cap so were easily changed out.

Took a couple more tries but what I ended up with was an aluminum disc about the diameter of the can with a series of eight holes on about an inch and half diameter with four smaller holes in the center and it quieted it down nicely. A side benefit was because it plugged up the pipe some you end up getting more torque out of the motor than you would with a muffler that is straight through and has no back pressure.

It will still get a little loud as the packing burns out but I am currently on a quest trying to find a better packing material for ALL my bikes.

A couple years later I bought an '03 WR450 that had a nice but loud FMF pipe on it. I built a real similar end cap for it and have been using it ever since with GREAT results!

Thats what I'm talking about guys!! Awesome info!


The idea here is the glass packs are dirt cheap, can be clamped on so replacement rather then repacking is a snap.

They ARE of the straight through design, which is where the insert comes in. Wish I had a picture of the baffle as its complicated to explain, your favorite aftermarket harley catalog will will surely have several to choose from. I havent started aquiring parts yet. was just looking for anything allong the lines maybe being done before.

My WR currently has the nice looking stainless muffler, I'd kinda like to keep that at the moment. But also want the bigger yz exhaust, so I'm a bit torn. And without much riding while I wait for to get legal, hard to tell if I like the performance of whats curently bolted on.

My 2003 WR450 has the stock exhaust on it. It's stainless and uses baffles - it doesn't appear to come apart. It has a spark arrestor tip, but is still very loud. I'm trying to find something else for the right price - I have an 08 YZ450 can but of course it mounts differently than the steel frame bikes so I'll have to extend it in order to get it working.

TOTEN, Thats the muffler I currently have think I'm gonna stick with it, I like the look as mine isnt beat up and shined up well. Still might play around with inserts though. check out inserts for harleys, adjustable and come in various sizes.

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