Expansion Chamber possible?

Discussion in 'Performance Mods' started by SlicerDicer, May 31, 2007.

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  1. SlicerDicer

    SlicerDicer Guest


    I am considering getting that expansion chamber when it comes back in stock. I will need to do a bit of modification as philcred did but I think this one is quite similar. Its cheap enough too.

    And the silencer is replaceable that is nice for when garbage builds and blocks it.

  2. What advantages do these provide. I see them on 2 stroke dirtbikes an such...

    Is it comparable to aftermarket headers/exhaust on a car.

    Performance, efficiency, sound and such?
  3. SlicerDicer

    SlicerDicer Guest

    it controls the sound waves and pressure waves or something like that to force air into the engine doing a super/turbocharger like effect. It usally only targets a special rpm number to give maximum performance. Most of the time they are custom created per engine but with these we have to take what we can get :grin:

    BTW feel free to slaughter my explanation if I am wrong :razz:
  4. OldPete

    OldPete Guest

    You are close enough. :grin: :cool: Google Gordon Jennings and read one of the first four hits that will explain expansion chambers in great detail.
  5. Herrmanator8

    Herrmanator8 Guest

    on my kx85 and our cr250 it seems to me that the purpose of the expansion chamber is when the powerband kicks in, it allows the exhaust to flow freely so that the engine can run at extremely high rpm's. im not shure about this but it seems to be useful...

  6. Joshboy

    Joshboy Guest

    what would happen if i just took off the exhaust pipe completely?
  7. Alaskavan

    Alaskavan Guest

    I haven't Google'd Gordon Jennings, but my guess is that it "might" improve bottom end performance and seriously decrease top end performance. Oh yeah. It would probably p*** off the neighbors, and perhaps invite official intervention.
  8. Removal of the exhaust system typically results in less low to mid range power BUT improves top end....Not to mention being a "bit" louder! ;-O

  9. azbill

    azbill Active Member

    no exhaust can also mean running lean
    air gets sucked in through exhaust port :shock:
    lust a word from experience :lol:
  10. Ghost0

    Ghost0 Guest

    I think SlicerDicer is close, but I think I would get this pipe instead.
    Some mods will be required but it will be a huge improvement over stock. Because it was not made specifically for the motor/carb combo (70cc China unit) some tuning will be required. Depending on many variables, gear ratio especially, you will either need to increase or decrease the distance from the exhaust port to the end of the pipe. The shorter the pipe, the more top end and the longer the pipe, the more bottom end. If I had to guess, since the pipe was made for a 49cc engine, I would start with it longer and shorten it an inch at a time until you reach your desired results. You can use fiber reinforced silicone tube with hose clamps for your tests so you don't have to weld it every time. I know I will be buying one as soon as I get my moto-bike complete.
    Last edited by a moderator: Oct 24, 2007
  11. Hard rider

    Hard rider Guest

    Does anyone know where to get the reinforced silicone tube and also are there any other hoses that can be used on the exhaust?
  12. Yes....Not only are they possible...BUT MAN the POWER!!!....Took awhile for me to build this one for the Dax 70 (actually the chamber/silencer are production pieces but the lead in / header had to be custom fabbed for correct length....
    Deathe Race here I come! ;-)...I hope the pic works....
  13. Oops pic did not work...I will try again...

    Attached Files:

  14. Whew....worked that time...File was too large to start with...But anyways, the long header
    helps the low end torque a lot....I am running a 36T on this bike and it pulls Bellview Ave (a steep street)...WAY WAY better than stock....Also can do some engine only starts from a standstill (no pedaling)....Wow what a difference....I'll have to look into jetting tho...seems to peter out around 40 or so....Hmmmm (just kidding to know for sure...I'll have to re hook the speedo up cause the magnet flew off after earlier testing)
  15. mickey

    mickey Guest

    Holy cow!
  16. azbill

    azbill Active Member

    hopefully, you will clean up the piping a little ?
    looks rather bulky right now, but you are getting it done finally (I've been waiting for more about it)
    I did notice you aren't running one of your own sprockets :lol: :)
  17. HI AZ,

    Heh heh....you caught me with that sprocket thing.....Those 9 hole mounts frustrate me sooo much when trying to get the sprocket perfectly aligned that I didn't even attempt to change the old one out!

    Yes, the pipes are a little clunky but nobody local could custom bend the pipe to fit....Had to get the header length long enough for tuning purposes....seems pretty good now but could experiment more....Been thinking about making a dyno for more accurate
    tuning....I am going to try to get a custom header pipe made but had to get the prototype done first...If there ends up being enough interest maybe I can add that to the sprockets! ;-)
  18. Alaskavan

    Alaskavan Guest

    Andy, Could you use some of that flex pipe they sell for automotive exhaust? I've seen it in diameters under 2", but I'm not sure how easy it would be to get, or if it would bend enough, etc.
  19. Hi Alaska,

    Thanks for the idea....I had looked locally at the auto stores (Pep Boys, Advance Auto Etc...) for a flexible exhaust pipe....The smallest diameter I could find was I think 2 inches...I also saw a 1 1/2 inch flex pipe but neither pipe could be bent at a tight enough radius to make it all fit....I thought about using electrical conduit (EMP or was it EMT pipe and bending it...even bought the tube bender but the radius was not tight enough still....a hydraulic shop tried to bend this electrical conduit but it kinks at tight bends).....Finally I figured I could go to a muffler shop to see it that would work but the smallest they could bend was 1 1/2 inches....I have't done it yet but the one option that will work (other than the plumbing pipe method) is to have a local hydraulic shop bend me some hydraulic pipe (like they use on heavy equipment) this would work the owner assured me and even showed me some very tight bends he made on similar tubing but since I was primarily working on a prototype to get the lengths right I didn't opt for the added cost of having them bend me up the pipe....Ultimately, if I get the pipe just right...I will probably have the whole assembly shipped to a shop in CA to have the header pipe made....that shop is a manufacturing facility that could keep the dimensions on file to make copies of it should there be enough interest here or elsewhere for a tuned pipe....Really could use a dyno tho!
  20. Ghost0

    Ghost0 Guest