MB newbie - Question about 4-Stroke flexible exhausts

Discussion in '4-Stroke Engines' started by deuskc, Jul 12, 2016.

  1. deuskc

    deuskc New Member


    New member to the boards and the MB hobby as a whole and these boards have been extremely helpful. I'm currently purchasing components for my first build. I've picked up one of the 49CC HS-142 4-stroke kits, a cruiser style bike, new front & rear brakes, etc.,

    I have a question about "after-market" exhaust modifications that I've been reading about on these boards. I've decided to go with the flexible exhaust set-up seen in several threads both for the versatility of placement on the frame and the reported performance boosts to torque.

    Some old, dead but relevant threads:

    In threads on these systems it states that the length of the system is critical to its performance with the ideal length of the exhaust for a HS motor being 28.5". However, as overall noise is a factor for me, I would also like to attach some type of muffler to the end of the system. So my question is, do I need to include the length of the muffler within this 28.5" measurement or do I just need a 28.5" flexpipe and then I can attach whatever muffler I pick? And for mufflers, are there specific styles/types that are the most efficient at noise reduction?

    Thanks for any input

  2. jaguar

    jaguar Well-Known Member

    an open pipe has a pulse reversal due to it being open.
    with a muffler on you usually kill that reverse vacuum pulse that the engine can make use of. so then the distance doesn't matter.
  3. KCvale

    KCvale Motorized Bicycle Vendor

    There is no such thing as a 'performance boost' to be gained from the exhaust on a 4-stroke, it has valves.
    Just keep your rocker arms adjusted and let the exhaust flow as free as possible.
  4. jaguar

    jaguar Well-Known Member

    return waves get past the valves just the same as getting past an open port.
    It's just that the design of a 4 stroke is such that it is very efficient and needs very little help.
    This is the fad now for 4 stroke motocross bikes:
  5. deuskc

    deuskc New Member

    Thanks for the replies. For now I've just ordered the flexible pipe and will go from there.