Well I just had to say this and see if anyone else has experienced this

Discussion in 'Motorized Bicycle General Discussion' started by mapbike, May 27, 2011.

  1. mapbike

    mapbike Active Member

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    I put a SBP expansion Chamber on one of my bikes that I had a straight pipe on before and it actually seems that the torque has dropped on it, dont get me wrong here it still runs good but it doesnt pull the hills as good as it did with my home built exhaust.

    Just curious if anyone else has experienced this.......

    I know that the expansion chamber is a huge step up from the stock mufflers that come on these engines but is it really the best you can get on them..?

    after all these are not engine that are very high tech with reeds and all....

    Just curious of others finding and if they are simular to mine..

    Peace
     
    #1 mapbike, May 27, 2011
    Last edited: May 28, 2011
  2. 5-7HEAVEN

    5-7HEAVEN Well-Known Member

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    Because your exhaust is now more efficient, your air/fuel mixture is lean and needs to be adjusted.
     
  3. Mike B

    Mike B New Member

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    Yeah, that could work.

    The pipe is supposed to stuff the mixture back into the cylinder, but if you ain't got nothin' to stuff...
     
  4. mapbike

    mapbike Active Member

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    what..........?

    my mixture is fine, I have rejetted all my engines multiple times getting the mixture correct for every cahnge I've made.


    I'm not asking anyone there opinions on my engines or how they run I simply ask if anyone else has experienced the same results as I have as far as the expansion chamber NOT making any noticable power increase over just having a good free flowing exhaust on these china girls.

    I'm very good at tuning these engines so I'm not looking for any advice in that area.

    thanks for the words though

    Peace
     
    #4 mapbike, May 27, 2011
    Last edited: May 27, 2011
  5. mapbike

    mapbike Active Member

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    Read the post carefully.......I said my bike ran better and pulled harder before I put the expansion chamber pipe on it.....it still runs good with it but seems to lack the hill pulling torque it had before I put the expansion chamber on it.

    Peace
     
  6. dag_29307

    dag_29307 New Member

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    I don't have very many hills that I ride on but where I needed to pedal before I don't now. I haven't ever used anything but stock exhausts before either. So I may not be the best answer for your question.
     
  7. Pablo

    Pablo Master Bike Builder & Forum Sponsor

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    If the expansion chamber isn't making more power than the stock exhaust then something is not tuned correctly, IOW you aren't getting the full power on the pipe. Could be your mixture, but if you have specifically jetted the bike for the expansion chamber, then it's pipe tuning. You should definitely feel the bike come on the pipe, if not adjust the overall length from exhaust port to chamber.
     
  8. Mike B

    Mike B New Member

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    Nah, he said his straight pipe works better than the expension pipe.
     
  9. mapbike

    mapbike Active Member

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    I never said I was running a stock exhaust............and I have no idea what IOW means a little english here please

    I said I ran an exhaust I made that pulled better on the hills than the expansion pipe does, the length of the expansion pipe is still as it came I never shortened it for fear of loosing my low end pulling power, like I said I'm NOT trouble shooting what I have...... I know what I have and how it works I'm just asking if others have had this same experience.

    it seems no one is redaing and understanding what I ask and what this thread was started for.

    I LIKE THE EXPANSION CHAMBER ON THE BIKE JUST FINE....... I just haven't seen any benefits to it over the exhaust I've made and put on my bikes like this one.....
     

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  10. mapbike

    mapbike Active Member

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    ok I figured it out IOW means (In Other Words)......got it!

    Peace
     
  11. dag_29307

    dag_29307 New Member

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    I like that home brew exhaust what did you make it from and where can I find the parts? How loud is it?
     
    #11 dag_29307, May 28, 2011
    Last edited: May 28, 2011
  12. Pablo

    Pablo Master Bike Builder & Forum Sponsor

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    I know you are not running a stock exhaust. I read that. I was writing in general terms for the general reader.

    Here's a conceptual view of what I think you are experiencing. At low rpms BEFORE an expansion chamber can have full effect, it is possible that a straight larger diameter pipe will produce slightly more power. Especially detectable in a single speed bike. Now there is no way physically such a set-up will produce overall higher peak power within the most efficient powerband of a 2-stroke engine. In such a situation it would be basically trading off a nice torquey mid-high peaky on pipe powerband for a slightly more torque in an RPM range where the engine is not the happiest. This of course would not be a good choice for a bike with gearing where one could match that power band as needed with gears.
     
  13. baadboy

    baadboy New Member

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    i have the same problem but not a lot of hill where i live but i ha better torque with stock pipe
     
  14. mapbike

    mapbike Active Member

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    I made the flange that goes on the engine myself so that it is perfectly matched to the port and then the pipe can be purchased at NAPA auto parts, it is 1" exhaust flex pipe, the chamber at the end of the pipe is a Venom Energy Drink can, I cut a split it the top of the can about an inch down so iwould expand so the 1" flex pipe would fit inside it and then I secured it to the flex pipe with a hose clamp, I then drilled three 3/8" holes in the side of the can toward the back so the holes in the can point toward the the ground when the can is turned on it's side, this makes the exhaust come out pointing down and makes it a bit quiter.

    This isn't by any means a quite pipe but not nearly as loud as a straight pipe, I like it and if I wanted it quiter I could just put one of those Copper dishwashing scrubby pads in the can and that would make it quiter.

    This bike has faster top end and pulls the hills around here better with this pipe than it did with the expansion pipe I had on it, not sure why I just know it does run very nice with this set up

    and my other bike still has a SBP expansion pipe on it and it runs good with it also, I plan to leave it on that bike because it runs good enough and it looks good also.

    I made one exhaust with a 3/4" pipe all the way back and it didnt run well at all, but when I went up to the 1" ID pipe it made a difference I can feel and see on the speedometer.
     

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  15. dag_29307

    dag_29307 New Member

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    Thanks for the info. I'm gonna have to try that. where do you get that venom stuff? Never heard of it.
     
  16. Allen_Wrench

    Allen_Wrench Resident Mad Scientist

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    'Fraid he's right, Map. That expansion chamber is good for giving you torque where torque is usually lacking, but only at a certain RPM. In order for it to cover a RANGE of RPMs from high to low, it would need to change size, or to maybe work like a slide trombone (HEY! there's an idea! Maybe add a bi-metallic linkage to make it automatic! Hmmm...I wonder if there's money in that?) Anyhoo, it's still a good pipe, it's just not real adaptable.
     
  17. mapbike

    mapbike Active Member

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    I have no fuss about what Pablo said, I understand how the expansion chamber works and I know what it's advantages are under certain conditions all I am saying is that with my bikes I have not felt, seen or noticed any significant advantages to the expansion pipe verses the exhaust that I have built and put on them, top speed NO changemid range ????? maybe... NOT sure, low end torque, my pipes pull the hills better tahn the expansion pipe does in it stock length, this is the only point I'm making here, I have nothing against the expansion pipe and know that if it is tuned properly to a 2 smoker it does make a difference, I've had 2 stroke dirt bikes and my dad used to run the Yamaha 125 twins & RD 350's and I had an uncle that owned a Yamaha dealership and he raced the 2 smokers of the day and built some awesome racing engine so I have been around the 2 stroke stuff enough to know how it works, but these engines aint YZ 80, 125, 250 or the such and I dont find that the expansion pipe makes a noticable difference over my exhaust, now compeared to the stock exhaust the expansion pipe is far superior in every way but the 1" pipe on my engine does everything that the expansion does and maybe more as far as torque goes in my testing so far.....this doesnt mean that I may not find a sweet spot on that expansion and end up seeing a noticable increase over my home brewed pipe, but so far I haven't, that all I'm saying here.

    Peace
     
  18. mapbike

    mapbike Active Member

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    Heres what they look like before I caoted it with spray on truck bed liner.... I also use these for fuel tanks to carry onboard 6 of them is oughly 3/4 of a gal.
     

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  19. Allen_Wrench

    Allen_Wrench Resident Mad Scientist

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    I think you might have yourself a really good home-made pipe there, if even an expansion chamber can't sell it short. I think if you continued tweeking it you'd come out with something pretty well-suited to your specific bike. If you've made good use of your knowledge and experience with that bike, then you may not find many aftermarket parts that'll make a WHOLE LOT of difference over what you can do yourself.
     
  20. 5-7HEAVEN

    5-7HEAVEN Well-Known Member

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