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  1. #1

    Default Custom Exhaust Diameter question/problem

    Ok so I have a 2001 Blast with a velocity stack, outerwears filter, 46/175 jetting, and a custom exhaust. The exhaust is made from a Sportster header cut down. It is a 1.75" diameter pipe. With no muffler (just straight pipe) the bike works flawlessly, pulls hard all through the rev range. The problem is when you put a muffler on or even just an exhaust baffle in the pipe, it bogs HARD at wide open throttle. I've tested this a few different ways, and the only way that it doesn't get that major bog is with a straight pipe.

    So my guess is that a 1.75" pipe flows enough air, but with a baffle or muffler restricting the pipe down in size it isn't flowing enough. So what's the solution? I was thinking about getting a step-up adapter to transition the header at the end to a 2.00" pipe and use a 2" diameter. Would that work?

    It's my wife's bike so she doesn't want it straight-pipe loud.

  2. #2


    Ok made a discovery, the header pipe I'm using is 1.75", and the cut down and modified sportster muffler I'm using has a 1.75" inlet and outlet, however in the middle of the muffler it necks down to about 1.5". Explains why with a straight pipe it had enough flow, but with any baffling it was bogging down. Too small of a pipe to flow enough air.

    So I'm keeping the 1.75" header, and I ordered a 1.75" muffler to try. It will be here Friday so I'll update with the results.

  3. #3
    Racer kwkride's Avatar
    Join Date
    May 2014
  4. Default

    I hope that it helps for you.
    Jim Hungate
    MSF #27339

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