SBP Expansion Chamber Questions

Discussion in 'Performance Mods' started by lordoflightaz, Apr 16, 2009.

  1. lordoflightaz

    lordoflightaz Member

    I suppose I could email SBP but I thought: Why not start a thread about this thing.

    I bought one! Now what do I do with it?

    My bikes have center kickstands, and I like them. So routing the expansion chamber is a puzzle, or pretzel if you will. I have included photos of my mocked up install. It fits perfect. and I will attach mounting bracket on down tube and rear tire strut.

    I added another 45 degree elbow so the pipe wraps around the tube. I know I will need to add another silicon coupler. I know that I have to move the chamber in toward the bike more but that is when I have the mounting bracket built

    Bike is RAWUSA 49cc with SBP shift kit high performance spark plug wire, (bike hit 25 MPH as pictured in second without porting anything)

    The questions about this:
    So how much should I compensate for the elbow and where should I adjust?
    Should I make it at the chrome end near the chamber?
    Should I shorten the straight pipe.
    Should I shorten both?
    Should I send it back? NO WAY. 'course Pablo and Ghost0 are thinking why did we let him order this

    Note: I'm asking this is before any adjustments are made so it runs better in higher gears.

    Attached Files:

  2. Ghost0

    Ghost0 Guest

    As long as you remove the same amount of pipe as you added you should be fine. I dig your creativity in mounting. You will lose a slight bit of performance due to you increasing the bending just past the exhaust header but it won't be much.

    If it were me I would remove the extra pipe at the joint where the silicone coupler is. You should then be able to still fine tune at the header.
  3. lordoflightaz

    lordoflightaz Member

    I guess the question is how much did I add? The elbow slides into the other elbow and the curved pipe. Would it be like a 1/4 inch?

    I can think of a way to measure the change in volume but not length, at least of the top of my head, by filling the the 2 pieces with water, pour it into a beaker and measure, add the elbow add water and measure again.

    Design is easy, execution the hard part
  4. Ghost0

    Ghost0 Guest

    The easiest way to measure is to use a piece of string. Run it along the center of the pipe to get the most accurate measurement. Start at the header flange and measure to the start of the expansion chamber. 13 inches would be a good start and you can shorten from there. Length is more critical than volume.
  5. lordoflightaz

    lordoflightaz Member

    The volume was how I was going to figure length but mind went numb trying to consider conversion. Now I will be working in "String Theory".

    Working with a 13" length as a maximum helps. If, I take too much out I will be in the middle of the down tube probably a bad idea, LOL.

    Need to relocate the CDI in any event so I may end up within the diamond for the pipe.

    Thank god I don't need to be a rocket scientist.
  6. Ghost0

    Ghost0 Guest

    Like I said I would remove the length initially at the end of the chrome pipe as it enters the silicone coupler just prior to the expansion chamber. This should still leave you some adjustment with the copper tube at the header.
  7. lordoflightaz

    lordoflightaz Member

    Got it down to 13 and am leaving it there for the moment. Took 1/2 inch from each end. WOT still bogs but just short of WOT call it SOWOT is pretty intense. I scare myself.

    Added benefit of this design I will never have to oil my chain again, LOL.

    Attached Files:

  8. Ghost0

    Ghost0 Guest

    I would bet money it is running rich which is why it bogs a bit at WOT. I had to lean the crud out of mine. I am running a .6mm jet, stock is .7mm.
  9. huckersteve

    huckersteve Member

    Hey Ghost- Did you make your own jet for the tuning or are we able to find/use existing jets for the stock carb??

    I am considering using a Dellorto Moped Carb for this reason..
  10. Ghost0

    Ghost0 Guest

    You can go either way, I just soldered and drilled mine but I know Dellorto makes a replacement jet. I just find it easier to solder and drill until I get it right than ordering 5 jets and end up just using the right one and have wasted money on the other 4.
  11. 350zdrftr

    350zdrftr Member

    from my little knowledge about gasoline engines you would want the exhaust gases to escape as easily as possible , the stock design works well in my opinion because it's a fairly simple design . I think removing the baffle would help open it and allow it to escape enough and drill a few holes in the bottom and it would equal performance of an expensive tuned pipe
  12. Ghost0

    Ghost0 Guest

    In case of a 4 stroke you are correct but a 2 stroke is a different animal. Because a 2 stroke does not have intake and exhaust valves they have difficulty pulling fuel/air in and also allowing unburnt gasses out the exhaust. An expansion chamber pipe uses the sound waves created by the exhaust traveling though the expansion chamber to assist in pulling a fresh charge of fuel/air and will also help close the exhaust port not allowing unburnt gasses to escape increasing the useable charge in the combustion chamber. Hands down the expansion chamber is the best method of bolt on performance you can get for a 2 stroke engine.
  13. Pablo

    Pablo Motored Bikes Sponsor

    This shows the concept pretty well.

    Relatively speaking our pipe is simply not that expensive.