PROPER exp. Chamber for HT engines!

Discussion in '2-Stroke Engines' started by G-Superior, Jul 12, 2010.

  1. G-Superior

    G-Superior Member

    From the past year or so i noticed that people where using pocket bikes expantion chamber
    One reason that they used is probably because they where cheap BUT one really negative thing about then is how they made/how the waves travels inside then!
    The pipe is supposed to be as smoth as possible so the waves are effective pulling and pushing gases and fuel in and out so the power is increased BUT in the connection beetwen the pipe that come from the exhaust port to the first cone in the expantion chaber the pipe taht is supposed to be welded where it meats the chamber they push it in about 5 cm!!!!
    This make the waves completly unefective.
    So to get over that you get the pipe out, cut it in half(in the belly section)LIKE IN PIC. 1) and then you have another 2 choices!
    you can cut both ends off where both pipes met the chamber(in the front side and in the silencer side) and get rid of the extra 5 cm or so that goes in the pipe and weld it all back together or you can just cut it in half and then grind the extra 5 cm inside the pipe with a gremel or a hand drill with those grinding stones.
    ANOTHER thing that matters is how long overall pipe is
    To short and it will be to peaky so the engine will be at full revs all the time to take advantage of the pipe an to long and it will not be good at all.
    The std. pocket bike pipe is WAY to short for a chinese HT 66 or 48cc engine
    they are only good for very high revs (something like 12.000rpm) which is no good for a HT (I think the chinese engineers are no good at measuring and making a good and effective pipe because even the std. pocket bike tops up at around 10.00 rpm which makes the pipe useless in the std bike)
    So to make it effective in the HT engine you would have to add a few cm to the belly of the std. expantion chamber
    At the moment I really have no idea how many it would be because i dont have a bike with a HT engine so all i can do is do it for a pocket bike.
    My pocket bike now revs like crazy and much more freely with the mooded pipe(i did not add any belly to the pipe because my bike is topping up at about 13.000rpm anyway)
    If any of you has a HT with a pocket bike pipe I really do recomment you to do it because its worth it the powerr that it brings
    Now how much belly you will have to add to it i really dont know, Its a trial of error and a bike dynamo(to measure HP) and tachometer(to mesure the RPM) would really help alot
    Hope I helped someone and any questions or anwser please comment

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  2. james65

    james65 Member

    Tuned Pipe

    I am not sure about the exact measurements, but this pipe added a lot of power to my bike. It was like a whole different engine when I made the change. Of course everyone tells me that the tube from the head should be less than 12 in. However this works for me so I will not change it.

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  3. srdavo

    srdavo Active Member