KTM 450EXC Muffler Rebuild

Discussion in 'Thumpers' started by StmbtDave, Jan 27, 2010.

  1. StmbtDave

    StmbtDave AKA Invisible Dave

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    I finally got fed up with the loud pipe on my '07 450EXC and decided to see if I couldn't do something about it. I removed the muffler from the bike and started the disassembly.

    [​IMG]

    Notice the hole in the middle of the can. After pulling the end cap and removing the innards, this is what I found.

    [​IMG]

    Only half the EXC muffler is actually packed for sound deadening. The packing is only wrapped around the smaller perf pipe shown on the right.

    [​IMG]

    The hole half way down the can holds what appears to be a large perf pipe, seen on the left. This is actually the Krizman spark arrestor. It is nothing more than a hollow pipe with a set of angled vanes welded in the center. Evidently, these vanes cause the exhaust to spin, keeping any sparks from exiting the chamber :dunno.

    [​IMG]

    Anyway, the arrestor unit has no sound packing except a thin layer between the screen and the outside muffler can. I assume this is simply to keep the outside can cooler.

    The stock EXC muffler can is 18" long but only half of it is actually a muffler :huh. No wonder it's so damn loud. I can see the solution is to ditch the Krizman and pack the entire can.

    I picked up a used 2-smoke muffler with a full length perf pipe from the local KTM dealer. I pulled it apart and removed the perf pipe.

    [​IMG]

    This perf pipe is 1 3/8" diam, which is smaller than the 1 3/4" diam stock perf pipe, but it matches the diam of the pipe in my end cap. This will solve two problems. It will easily attach to the end cap and it will slide inside the stock perf pipe. This will allow me add a screen type spark arrestor inside my new muffler.

    I cut the smaller perf pipe just long enough so it would extend about 2" inside the larger perf pipe. I welded a small ridge around the smaller pipe which will hold a washer in place. I then wrapped some stainless steel wire mesh around this section of the pipe and slid the washer on to hold it in place. Volla, a spark arrestor :deal.

    [​IMG]

    When assembled, the mesh slides inside the larger pipe and the washer seals the connection between the two :clap. I then wrapped the entire assembly in the remaining wire mesh from the Moose packing kit.

    [​IMG]

    This was then wrapped with the fiber packing and slid back into the stock can.

    I have not yet had it measured with a sound meter but this is how a muffler should sound :clap. It's very much quieter and what was a loud braaaap when you twisted the throttle is now a smooth purr. It's not a constricted sound, but rather a well muffled straight pipe sound. It may not be perfect but it's a hell of a lot better :deal.
    #1
    Lewilewi likes this.
  2. Yellow Pig

    Yellow Pig Allergic to asphalt! Supporter

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    Nice!
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  3. Hayduke

    Hayduke ///SAFETY THIRD/// Supporter

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    That is a great mod, Dave. My stock pipe on my 525 is just too loud... It's ok at idle but has a real bark when you get on the throttle. I need to start looking for a 2 smoke pipe... :deal Thanks!
    #3
  4. ChrisC

    ChrisC Amal sex?

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    Dave,

    I've got a dB meter, if'n you want to test it. We really should have baselined it before you tore into it...
    #4
  5. jjustj

    jjustj Long timer

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    Other than the can on stock being stamped forestry approved spark arrestor.. I want one!!!!! I don't have a shop or garage .
    #5
  6. Esteban

    Esteban Banned

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    Dave,

    What you did is similar to what I have in mind. As you know I now am the proud owner of a SX can and the EXC can my bike came with. On the exterior they are of the same dimensions. However, the ID of the perforated core pipe and the end cap ID is larger on the SX mufler.

    Does anybody know where to buy perforated steel pipe in different lengths and diameters ?
    (The thought of drilling a thousand holes in a steel pipe gives me the chills.)

    When I do mine I think I will try to make a cone of the SS screen and attach it a few inches inboard of the rear outlet. Its going to be a few weeks before I get the time though.

    On a different note... shouldn't this thread be in the Rockies ?

    Steve
    #6
  7. Esteban

    Esteban Banned

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    Chris,

    Want to come over and test the dBs on my SX and EXC sparky cans ?

    I'll be hot to trot in mid Feb.

    SG
    #7
  8. mountain eagle

    mountain eagle terrorist

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    Actually... wouldn't that make for nice get together? It would be nice to test the husky too......
    #8
  9. ChrisC

    ChrisC Amal sex?

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    Steve,

    Decibels and beers sounds about right. I have the older style analog meter, but it should work fine. We could use the SAE J1287 test. 20" from the exhaust tip - 45 degrees @ 1/2 max RPM. How will we determine RPM on your tach-less bike(s)? Guess we could estimate it...

    What say y'all? :1drink

    http://www.parks.ca.gov/pages/1140/files/j1287_199807.pdf
    #9
  10. cRAsH

    cRAsH Banned

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    I can tell you it was RFL.

    Really Frikkin Loud. :huh

    Nice work, Dave!
    #10
  11. cRAsH

    cRAsH Banned

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    They're so cute when they jump out of the nest... :wink:
    #11
  12. mountain eagle

    mountain eagle terrorist

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    Sounds good......... where and when?


    #12
  13. Beemer Pat

    Beemer Pat ...

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    Nice mod Dave. :nod I'm sure all the rockies guys here will want to hear it to see how you have done. :thumb
    #13
  14. StmbtDave

    StmbtDave AKA Invisible Dave

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    It's like riding a Harley, you don't hear the noise when it's behind you :ear. Loud pipes really do save lives as I'm still here to attest :rofl. Actually, the reason it was RFL was when I disassembled the muffler, there wasn't one thread remaining of the packing I put in last year. It had totally burned out :eek1. I have no idea how long I had been running an empty can.
    #14
  15. cRAsH

    cRAsH Banned

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    Ask Maaaaahk. :lol3
    #15
  16. StmbtDave

    StmbtDave AKA Invisible Dave

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    Steve,

    You're going to have a hard time making that SX pipe quiet because of the large diameter perf pipe. My '07 EXC came from the factory with a piece of pipe welded into the end cap pipe.

    [​IMG]

    This reduced the diameter of the end pipe from 1 3/8" down to 5/8" :eek1. Less than half the diameter reduced the cross section area from 1.48 sq" down to 0.31 sq", an 80% reduction! This really choked down the exhaust but was necessary to meet the U.S. EPA Noise Emission Requirements Of 80 dBA (so says my sticker :deal). Of course, as we know this was also required since KTM only uses half a muffler :lol3.

    I suspect your SX pipe has a 1 5/8" diam. This gives a cross section area of 2.07 sq" which is almost 7 times larger than my stock EXC that met sound requirements. You can't stuff the can with enough packing to get it "quiet" without choking it down a bit.

    Dave
    #16
  17. ganshert

    ganshert not sleeping

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    yup

    here

    1", 1 1/2", 2", and 2 1/2"
    #17
  18. Hayduke

    Hayduke ///SAFETY THIRD/// Supporter

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    So....

    Has anyone found a "fix"?

    I love nearly everything about my 525, except the NOISE! I have a freshly re-packed stock pipe and the bark when you get on it is just terrible.

    Anyone try a turn down tip? Would this have to be fabricated or is there one available?
    #18
  19. cross-country

    cross-country .

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    I have a turn down tip on my 08 450, different can but I would imagine it would fit any PMB tip. I know they make a PMB tip for the 525 can. I am not convinced the turndown tip makes it all that more quiet, accept from the rider's perspective.

    On a slightly different note, I have a friend that up until recently raced AMA supercross. When a db rule was first put into effect some of the privateers were caught off guard for the first couple of races until they could get the parts modify their exhausts. One of the cheats these guys would use to pass sound tests on their bikes was to cover the airfilter so as hide any intake noise. The bikes would start and run but just barely. I wonder if sound proofing the airbox cover with a material like dynamat would help? Just a thought......:dunno
    #19
  20. cedric

    cedric Been here awhile

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    There was a guy on KTM Talk that added a CRF-X tip into his RFS pipe. I never have much luck with their search tool, but I'll see if I can find the thread.
    #20