How about this expansion pipe

Discussion in 'Performance Mods' started by FelipeCobu, Aug 1, 2011.

  1. FelipeCobu

    FelipeCobu Member


    I'm typing from Brazil, around here isn't that easy to get performance parts for the motorized bikes.

    So I was searching for a an expansion pipe and found one model for Mobyllete (some kind of motorized bike witch uses the AV-10 - 50cc 2stroke - engine).

    There is a pic attached.

    So do you guys believe this model is suitable to a 66cc/80cc Chinese bike engine? This weekend I removed the cap of the stock exhaust pipe and found its s chambers I don't believe this part is helping the engine in its performance.

    Thanks Very!

    Felipe Cobu

    Attached Files:

  2. motorpsycho

    motorpsycho Active Member

    yes that may increase the performance, but there isn't a flange on the end that will bolt up to the cylinder on the chinese engine. You could weld a flange on it by cutting the one off of your stock pipe.
    The other thing is, the length of the pipe overall, and the curve of the head pipe.
    It may not fit onto a bike very well and you may have clearance issues.
    The other thing to take into consideration is that the length of the head pipe (the part before the chamber) will determine what rpm will give the most power.
    I'm not sure what does what but i beleive that a shorter head pipe length will give more bottom end power, where a longer head pipe length will give more top end power.
    I may have that backwards tho because i am not 100% certain on it.
    anything other than the stock pipe and muffler will help these engines perform better.
  3. FelipeCobu

    FelipeCobu Member


    About the modifications i'll have to do a friend of mine owns a garage and is a TIG Welder too, I already have a spare flange that was plasma cutted from a 3/8 steel board. Surely I will have to do some tweaks to the pipe. What I needed to know was if worth it.

  4. motorpsycho

    motorpsycho Active Member

    I have no idea, you don't have a price listed. How much is the pipe?
  5. FelipeCobu

    FelipeCobu Member

    What I need to know is it worth in terms of performance not cash. This answer i already have!

    Thanks again motorpsycho!
    Last edited: Aug 2, 2011
  6. HeadSmess

    HeadSmess Well-Known Member

    your friend has a tig welder. theres only one answer.

    cant buy it? make it. heaps of software online. all you need to do is measure the engines timing. also heaps of info online on doing that. and porting. how removing what affects what :)

    a pipe is an individual creation for a specific engine. port timing, rpm, capacity, port sizes, compression ratio, fuel type, exhaust gas temp... phew!

    i make it sound is! without the software now available :D

    this isnt the best for top performance pipes but does give nice visuals of what affects what with basic pipes :)

    the pipe you have shown is a thrown together bunch of cones. the angles and lengths are critical and it just doesnt look right to me for ANY engine... (lead in cone should be about 6-8 degrees taper, reflector should be twice that and half the length, etc etc...) it may do something other than make noise. maybe. at what rpm? with what porting? will it hold it up hill?

    you spend a solid two days with some basic metal tools and a welder.... with a good design, and then feel the results? lol. no more to say :D

    and theres the bonus of having made it yourself. knowing how to modify it. making it a neat fit...valuable skills to learn. you should end up with something that will put any shelf bought pipe to shame :)
    Last edited: Aug 2, 2011
  7. FelipeCobu

    FelipeCobu Member

    After some researching a I have to agree with you.

    That exhaust is just for noise, don't have the "belly" section, and appears to be inverted in shape.

    I will measure the parameter to build it right then I will see if its possible no modify something I found in the local market or do it from the scratches.

    I've been reading some of your posts and there are lots of interesting information.