1. Adventure Rider Print Magazine!
    We're doing a print magazine this November - 128 pages of high quality adventure riding stories, photography and interviews!

    Click here to purchase a copy for $9. Limited copies still available.
    Dismiss Notice

"Homebuilt" expansion chamber

Discussion in '2 smokers' started by dorkpunch, Jan 28, 2011.

  1. dorkpunch

    dorkpunch Oops...

    Joined:
    Aug 2, 2006
    Oddometer:
    5,968
    Location:
    Blackfoot, ID

    Yup, and yup. Bells book says to cut a straight line clear through, then cut an angled chip out to the center, put the angled chip on the other side, and weld it all back up. The way you said would be a lot less welding though...
    #61
  2. dorkpunch

    dorkpunch Oops...

    Joined:
    Aug 2, 2006
    Oddometer:
    5,968
    Location:
    Blackfoot, ID
    Its a 3 stage pipe, so yes, all three of those are part of the cone. The "head" pipe is 74 mm long- hardly a drop in the bucket when you add it on to the rest of this giant...
    #62
  3. dorkpunch

    dorkpunch Oops...

    Joined:
    Aug 2, 2006
    Oddometer:
    5,968
    Location:
    Blackfoot, ID

    Huh, hadnt heard that. Kinda cool, might have to give that a go!
    #63
  4. RecycledRS

    RecycledRS Along for the ride

    Joined:
    Nov 2, 2008
    Oddometer:
    1,050
    Location:
    Vancouver Island
    While creating a nice gradual bends in the cones and centre section looks great it is really not all that important as far as power output is concerned. The key is that you are really just reflecting pressure waves in this portion of the pipe as it is more than capable of handling the gas flow. The first section of pipe is less forgiving however and care should be given to smooth its transitions and curves.
    #64
  5. anotherguy

    anotherguy Long timer

    Joined:
    Jun 18, 2009
    Oddometer:
    15,491
    Location:
    the hills
    In additional it's actually quieter than external stingers. The stinger is basically a pressure relief valve so placement isn't as critical to performance as diameter and length.
    #65
  6. EvilClown

    EvilClown Standing by to standby for a possible disregard Super Moderator

    Joined:
    Sep 3, 2006
    Oddometer:
    20,044
    Location:
    In the shadow of the Uncanoonucs...
    Hey, Dork! Thanks alot! I now have a burning desire to build a pipe.:bluduh




























    Other than a KDX they're all 4-strokes. :lol3 'Cept for that stray Jawa that snuck in...

    Loving this thread!:clap





    :lurk
    #66
  7. motometal

    motometal i like motorcycles

    Joined:
    Aug 19, 2007
    Oddometer:
    4,357
    Location:
    Baja, Motorcycle Heaven
    I "made" one of those for my TM125 by coming up short on a jump or two.
    #67
  8. markk53

    markk53 jack of all trades... Super Supporter

    Joined:
    Dec 20, 2007
    Oddometer:
    19,819
    Location:
    Delaware Ohio
    I did too, going over a railroad track. Talk about a major loss in power! It barely ran. Had to cut it and pound the pipe cone round again.
    #68
  9. dorkpunch

    dorkpunch Oops...

    Joined:
    Aug 2, 2006
    Oddometer:
    5,968
    Location:
    Blackfoot, ID
    Barf on a stick. Apparently, I wasnt on my groove today, and so I think my progress looks like crap. Oh well, here it is anyways.

    Turns out making the pipe bend is freaking hard. I tried the first way by cutting the pipe straight in half, then cutting a sliver off like so:

    [​IMG]

    Then tack the sliver on to the other side of the pipe:

    [​IMG]

    Then tack the two pieces of pipe back together:

    [​IMG]

    And weld it all up.

    [​IMG]

    [​IMG]

    Originally, i was thinking I would make the pipe s-bend under the engine and come out on the right hand side of the bike. Now I'm thinkin a couple more little bends and it can just go straight out along the left side. Here's where its at now.

    [​IMG]
    #69
  10. ac05jn

    ac05jn n00b

    Joined:
    Feb 19, 2011
    Oddometer:
    1
    [​IMG]
    #70
  11. Grider Pirate

    Grider Pirate Long timer

    Joined:
    Sep 28, 2007
    Oddometer:
    1,686
    Location:
    LV, NV
    +1
    Jennings book* also showed the method you used. It's really difficult to execute well. I rode a dyno doing two-stroke pipe design for 4 years. I made pipes the hard way (like the book) and the easy way, like above, and ran them on the dyno. Guess what? If there's a difference, it's too small to measure.
    Welding: with a good fit, lay your '0' tip on the pipe, nearly parallel. Don't hurry. When the sides begin to melt, back the tip up slightly and the sides should fuse, then move the tip forward 1/8 to 3/16" or so. You'll get a feel for it eventually. In welding many hundreds of pipes, I used welding rod only on the header and stinger.
    Here's a link to more than you want to known about two stroke pipe design. THE SINGLE MOST IMPORTANT THING TO GET RIGHT IS THE TUNED LENGTH. It's a simple one line formula. Exhaust open in degrees times 1700, divided by the RPM you want the peak at. You can further simplify it by assuming 180 degrees exhaust timing, since most bikes are pretty close. Then the formula is simply 30600 divided by your target peak RPM.


    * http://www.datafan.com/TunersHandbook/2-strokefiltered.html
    #71
  12. svejkovat

    svejkovat Been here awhile

    Joined:
    Jun 23, 2009
    Oddometer:
    856
    Sometimes it's easiest to draw to scale on paper and fit the model to your application to make rough measurments for bends and clearances.

    Really simple rule.... measure the angle needed, divide that angle by TWO, cut THAT angle, rotate your paper cutout 180 degrees, there's your original angle (same of course applies to real tubing). You can just keep doing this down the line on a tapering (or not) stretch. Gets trickier when you start working in a third dimension (compound angles), but the model gets you some way there.

    For mocking things up for over all visual fun there's always Google Sketchup...
    with a tapering plugin from the following source....

    http://www.drawmetal.com/moreabouttapermaker
    http://www.drawmetal.com/download

    Just a rough quick example that took one minute with sketchup....
    [​IMG]

    All you do is draw a line in any length, any curves or section lengths, putting angles where you please. That line then describes the center of your model. Use the plugin above from the dropdown menu, enter the beginning diam and the end diam, click, and done. The one above was so easy since it was in one plane/dimension. Figuring compound bends/angles is a bit trickier.



    Grider Pilot, thank you for that link. It's going to be an interesting read. I plan on playing around with this stuff a bit the rest of this winter.
    #72
  13. dorkpunch

    dorkpunch Oops...

    Joined:
    Aug 2, 2006
    Oddometer:
    5,968
    Location:
    Blackfoot, ID
    Definitely going to have to look into that tapering plugin for Sketchup. Is there any way to then take each section and flatten it out so I could print it and use it as a pattern?

    Havent had a lot of time to work lately, but i've been puttering a bit. Got it twisted up enough to mount on the bike for a test run tonight. I'm not real pleased with my work on the twisting, I will probably come back and build a new first cone and re-do all the bends. Its good enough for now, its getting close to riding time!

    Tried the second method of cutting, it works pretty good. Its a bit harder to guess on the angle your going to get when your done but its a heck of a lot cleaner when youre welding it up.

    [​IMG]

    [​IMG]

    Bending it back the other way:

    [​IMG]

    And the test run. Note the helpers. Right after I took this picture my youngest opened his mouth and stuck it RIGHT behind the pipe. Smoke was litterally bouncing out of his mouth. He thought it was great- I wasnt all that impressed.

    [​IMG]

    Still need to build some hangers, but good enough for now!

    [​IMG]

    Next step is fitting the rear sets on there... Got a start on it though.

    [​IMG]
    #73
  14. anotherguy

    anotherguy Long timer

    Joined:
    Jun 18, 2009
    Oddometer:
    15,491
    Location:
    the hills
    Cool project.
    #74
  15. dorkpunch

    dorkpunch Oops...

    Joined:
    Aug 2, 2006
    Oddometer:
    5,968
    Location:
    Blackfoot, ID
    I'm assuming you mean for each cone? Yes, you could, but if you have a little program that alls you have to do is type in those numbers and hit print and viola, instant template, why bother!? Trying to draw the first cone you would need something like a 10 foot wide compass. Could do it with some string and a pencil, but again, why bother? The program will even print cones with the ends cut at an angle, but I wasnt sure how I was going to route the pipe so I just built it straight and started cutting. Not pretty, but this was a learning experience. Someday I may take the time to actually lay one all out before I build it, but I find that sometimes the more prep you do before hand can lead to headaches later. Have to be flexible when your doing one-off projects.
    #75
  16. dorkpunch

    dorkpunch Oops...

    Joined:
    Aug 2, 2006
    Oddometer:
    5,968
    Location:
    Blackfoot, ID
    I'm sure theres a better way to do it manually, but look at the templates:

    [​IMG]

    A cone layout is two straight lines with an arc at each end. The two straight lines eventually come together in at a point. In order to draw the two arcs, you start at that point and go x inches, and draw the arc between the two lines. With the first cone on my pipe, the arc is EXTREMELY slight. If it were in a circle, the radius of the circle would be something like 10 feet. The two lines are darn near parallel, meaning where they finally come together (at the center of the circle) is a looonng ways away.

    Couple of examples- cone layout. extend the two straight lines until they cross:

    [​IMG]

    and you would get something like this:

    [​IMG]

    When you have the center point, you can draw the arcs. Basically just part of a circle, but on my first cone, its a really really BIG circle.

    I think I just confused myself more... :huh
    #76
  17. Strong Bad

    Strong Bad Former World's Foremost Authority Supporter

    Joined:
    Oct 29, 2007
    Oddometer:
    11,762
    Location:
    Omicron Persei 8
    Dude, lay your cones out on paper/cardboard. Putting both of the straight edges in the middle of your material is really wasteful. Put the edge of the pattern along the edge of the sheet and you'll have a "factory" straight edge to work with that you don't have to cut. BTW, stop using the galvanized sheet, the fumes are going to make you sick if not kill you.
    #77
  18. dorkpunch

    dorkpunch Oops...

    Joined:
    Aug 2, 2006
    Oddometer:
    5,968
    Location:
    Blackfoot, ID
    I just stole that pic off the web to show what I was talking about... Heres how I did mine:

    [​IMG]

    And mine is 20g cold rolled as well. :D
    #78
  19. supershaft

    supershaft because I can

    Joined:
    Sep 9, 2010
    Oddometer:
    9,116
    Location:
    San Francisco Bay area
    Cold rolled? I guess some do it otherwise? I am making some exhaust right now too. I got 20g 1018. If you can find it, I highly recommend 1020. Not for it's ever so slightly different stress analysis but simply because I have found it top be MUCH easier on band saw blades than 1018. I found the difference in that sense to be incredible.
    #79
  20. Strong Bad

    Strong Bad Former World's Foremost Authority Supporter

    Joined:
    Oct 29, 2007
    Oddometer:
    11,762
    Location:
    Omicron Persei 8
    Sorry, I thought the white stuff around the tacks were galvey fume residue, but now I see it is from a flux core mig. I must refrain from PUI after dinner.
    #80