Sick bike pipe rpm?

Discussion in 'General Questions' started by Wags, Sep 7, 2016.

  1. Wags

    Wags Active Member

    I have the sick bike expansion chamber. I'm pretty sure I haven't found the magic Length yet, I should feel the pipe kick in. I tried cutting down the header not by quarters, but by eighths just to make sure I didn't miss the mark. No changes. So I started over and cut a new piece of copper almost 3 inches longer than the header that comes in the kit and worked my way down again to just the fittings it takes to get around my down tube and connect to the first black exhaust pipe. The next step will be to either go even longer on the header or start taking length off that first black pipe.(opposite directions i know) Before I do either I would like to know from other people out there at what rpm does there sick bike pipe kick in? I know every pipe/engine configuration is different but i would like a reference point. Any help would be nice. Thanks

  2. jaguar

    jaguar Well-Known Member

    make sure each one also reports whether or not the intake is by reed valve or just by piston port.
    an expansion chamber is more effective on an engine with reed valve.
    change the header length one inch at a time.
    also consider the fact that pipe design has to match engine porting. And there is no pipe made for motorized bikes in a way where the design truly matches them. Most of them were originally made for pocket bikes.
  3. Wags

    Wags Active Member

    I have a reed valve. Im port matched. I have not changed my timing . I wonder if i need to go even longet or if i go go shorter. I have been to the point where I'm just fittings to get me to the first vlack pipe. Almost no copper header. Next will be to shorten the first black pipe. Or maybe I was never long enough. I added a couple inches to the size of the header that comes with it the firsr time before i worked my way down to nothing. Then started at 29, then 32 and then 34. After reading every article i can find I understand the sound wave and what causes the powe ree boost at certain rpms. Idk Maybe longer.
  4. Wags

    Wags Active Member

    Jaguar, that article on how an expantion chamber "really works" is amazing. This sick bike pipe is trouble all around. From stinger to header diameter. But now I really don't know where to begin. Open the stinger diameter or larger header diameter or length of header. Or maybe I'm asking too much out of this single, fixed baffle pipe that was oviously designed for something else.
  5. jaguar

    jaguar Well-Known Member

    definitely longer. pocket bikes rev really high and so need short headers. these bikes rev not very high and so need long headers.

    If you want it done right then do it yourself. I had zero experience and didn't have anyone to show me the way but I managed to make a pipe or two.
  6. skyash

    skyash Active Member

    All trial and error till some thing works
  7. Wags

    Wags Active Member

    I'm going to start so long it's going to take me two days to get where I need to go. I will have a verdict one way or another when this is all done and said. I already tried starting at 29 from cylinder face to reducing baffle and worked my way down. Then 32 and then worked my way to 29 an 1/8 th at a time. This time I'm starting as long as I can (40) maybe and then down from there a 1/2 to an inch at a time. My plug color is perfect but I think I might also try retarding the spark by one curve and also richening the air fuel a touch. So many factors. When you do as much asni did all at once it makes it difficult to isolate anything. I've spent more time reading different papers this past week then wrenching.
  8. KCvale

    KCvale Motorized Bicycle Vendor

    The SBP pipe is tuned for a 48cc, cut the straight copper piece in half for a 66cc.