Discussion in 'Performance Mods' started by geebt48cc, Jun 16, 2011.

  1. geebt48cc

    geebt48cc Member

    So, thinking about putting in about 25" length on (SBP) expantion pipe. So, do you think that would help?

    Last edited: Jun 16, 2011

  2. a/c man

    a/c man Member

    Help what?
    Are you putting the 25" before the chamber or after it ?
    Either way my answer is no it will not help.
    Longer head pipes will kill your upper rpm power.
    You may have ok bottom end but it will fall flat at the top end.
    I experimented with a long pipe, somewhere around 18" and it dogged.
    I think your best bet is to stick with the recommended 12 inches or so .

    I'm not sure what an extended stinger on the back end will do, but I'm sure an extra 25'"
    can't make a good thing better.

  3. jaguar

    jaguar Well-Known Member

    It all depends on what your top rpm is. (Higher rpm needs shorter length). The distance from piston to 60% of the baffle cone (2nd one) needs to jive with your top rpm, exhaust port open duration, and exhaust temperature (higher with high compression). Instead of becoming a math wiz at this its best to just experiment with header pipe lengths.
    For my bike which revs to 7500 rpm I needed 34 inches.
    Unfortunately most pipes have too steep a baffle angle to be of much use to anything but pipey pocketbikes. (steep angles give narrow powerbands). I just made my own pipe and with it I lost a little low end, top end power was the same even though it was made to have as broad a powerband as possible. After changing the jetting to be a bit richer I got the best low rpm power ever but lost some speed on the top end. Seems like I have to chose one or the other.
    Last edited: Jun 19, 2011
  4. jaguar

    jaguar Well-Known Member

    Last edited: Jun 18, 2011