49cc HS exhaust length too short??

Discussion in '4-Stroke Engines' started by Aaron Brown, Dec 29, 2016.

  1. Steve Best

    Steve Best Well-Known Member

    The largest problem with most of the China exhausts that I see in inconsistent diameter going to the muffler, not the exit from the muffler. Make sure it is a consistent diameter from port to muffler with no restrictions. No good to have 3/4" (19mm) pipe with 5/8"(16mm) restrictions at the flanges. Drill the flanges out to 19mm. I found no worthwhile gain from removing the baffles or endcap on any of the Chinese mufflers I worked with. More noise feels like more power but didn't prove to be.

  2. KCvale

    KCvale Motorized Bicycle Vendor

    Don't worry about your exhaust Aaron, it will work fine.

    There is no valve overlap with the HS 142-144F engines, take the valve cover off and you can clearly see there is a brief time both valves are closed (a degree or 2) at the same time so that settles that.
    Actually, set your vale lash while you have it open.

    Other than removing the stifling stock box exhaust, I can't see the specs on what you replace it really making any difference as long as it flows freer than the box, heck I use NON-EPA 2 stroke pipes on mine, without the catalyst part in them they flow pretty free, bolt right on and look cool for ~ $25.


    I get the biggest performance boost by just replacing the stock plug with an NGK 7544 (CR7HIX) Iridium spark plug.
    It is slightly longer so it actuality increases compression.

    A better air cleaner helps a little but really just for looks ;-}

    Another thing you can do is not direct the PCV hose back into the intake and route it into a 'catch can' but I haven't tried it, it just makes sense to me since those gasses are just waste.

    Hope that helps ya Aaron.
    Last edited: Jan 27, 2017
  3. gary55

    gary55 Well-Known Member

    There is valve overlap. A brief time where both the exhaust and intake are open at the end of the exhaust stroke and the beginning of the intake stroke. So you are wrong there. There is by far more than a couple of degrees that they are closed, like the entire compression and combustion stroke. So you are wrong about that too.
    Street Ryderz likes this.
  4. Street Ryderz

    Street Ryderz Well-Known Member

    There most definitely is a tuned length and it's like Steve said you can add length until you get it where you want then make the final pipe one piece with your tuned length!
  5. KCvale

    KCvale Motorized Bicycle Vendor

    Hum, possible with the wrong valve gaps I guess.

    That of course is first determined by the internal cam, but the rocker arm adjustments allow you to adjust that.
    In short, I set them so neither valve opens until the other is fully closed, and most engines come preset that way.

    If you think you can get any more meaningful performance from these little ~50cc engines with some some special sized pipe go for it and let me know what it is!
  6. Street Ryderz

    Street Ryderz Well-Known Member

    Kc I am shocked to read that you dont understand your engines needs and if you adjust your rockers as stated I dont see how you make any power!By doing that you limit lift and duration affecting its overall timing!This diagram shows the overlap relevant to all 4 stroke engines!

    Attached Files:

  7. gary55

    gary55 Well-Known Member

    The factory settings clearly state that the proper lash is set to allow for the most overlap without affecting performance when engine temps. reach over 320 degrees F. You yourself even state to adjust the valves as they seldom are set properly from the factory. When I am wrong about something I usually say oops I was wrong and learn what the real facts are. Try it out. It's pretty painless, and it makes one speak more knowledgeably in the end.
  8. KCvale

    KCvale Motorized Bicycle Vendor

    Yes indeed KC was wrong! that's what I get for just watching the valves in motion at the rockers and not measuring ;-}

    So what do you guys figure limiting yourself to a specific pipe gains you in performance?
    As much as say an NGK plug, or more like a high flow air cleaner, or really no more performance gain than a sticker that says 'tuned exhaust' hehehe.

    It was a simple question.
    I gave a simple answer.
    If this tuned 4-stroke pipe has any merit sure I want to know about it, but I still figure a sticker would be better than even worrying about it heheh ;-}
    Last edited: Jan 29, 2017