Quick question...need advice!!!

Discussion in 'Motorized Bicycle General Discussion' started by runnermike, Mar 11, 2014.

  1. runnermike

    runnermike New Member

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    I am wanting to build a custom exhaust for my 4 stroke. I have a ton of 7/8 handle bars laying around, but the header flange that fits my engine I want to buy has an I.D. of 1".

    Will the 7/8 tube slip right inside the 1" I.D. of the header flange? Will it cause any performance issues? Should I just find some 1" tubing? I really do not want to do that as I have a ton of handle bars with cool angles that will fit the bike nicely....

    Thanks in advance guys!
     
  2. CTripps

    CTripps Active Member

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    I'm not sure how the pipe diameter will affect a 4-stroke.. I'd suspect that a difference if 1/8" in dia. isn't a big deal, though there's probably someone else who knows more. If you do need to source a chunk of conduit to make a pipe, check for a local "Habitat for Humanity ReStore".. I grabbed a nice new full length piece of conduit there for a whole dollar not long ago.
     
  3. Dan

    Dan Staff
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    Mike, that is such a cool thought. I do not know but am wondering if even that wee bit of restriction close to the engine might cause some slowing of the engine.

    Just an off the top of my head thing but would some exhaust heat tubing. (can't find a link! forgot what it is actually called) as a spacer work?

    Dunno but really like your thought. Found this on the forum; http://www.google.com/cse?cx=partne...#gsc.tab=0&gsc.q=handlebar exhaust&gsc.page=1

    Really looking forward to seeing what you come up with.
     
  4. mapbike

    mapbike Active Member

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    In my experience restricting the exhaust is normally not a good thing and will hurt top end performance, although in some cases it will improve low end torque, but there is a fine line between what will help and what will hurt, the best way to know for sure ifthe smaller pipe will work in your application is to just give it a try and see what the results are, if you do slide the 7/8" pipe inside the 1" pipe I would suggest that you grind the inside of the 7/8" pipe so the exhaust doesn't hit a squared edge as itis squeezed into the 1"tube the term is shamfer which I may have spelled wrong here....lol!

    Probably low to medium rpms willwork about the same but as Dan mentioned you may loose rpm potential and power in the upper rpm range, just give it a go and see what you get is howI find out what works and doesnt on all my engines.

    Best wishes

    Map
    dnut
     
  5. wret

    wret Member

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    The 7/8 OD bar probably has in ID close to 1/2 inch. Compared to the 1 inch ID pipe, it would only have about 1/4 the volume. Huge difference.
     
  6. 2door

    2door Moderator
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    Wret,
    That would mean handlebars are 1/4" wall thickness? Sorry. Your calculations are way off, sir.

    Mike,
    1/8" difference will never be enough to impact the way your little engine will perform. I promise you. Use the 7/8" handlebar material. It is probably already chrome plated so your exhaust system will look good and work just fine.

    Tom
     
    #6 2door, Mar 12, 2014
    Last edited: Mar 12, 2014
  7. mapbike

    mapbike Active Member

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    I used a section of 7/8" handlebar as a lead off pipe on an expansion chamber exhaust I put together for one of my bikes and on the 2 smoker it still flowed good enough for me to reach speeds close to 40mph so I also think it will work plenty good, just give it a try and then you'll know for sure.

    Map
     
  8. maniac57

    maniac57 Old, Fat, and still faster than you

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    I agree, the 7/8 pipe will work just fine for a stock or near stock engine.
    You might gain some power if you go up in size 8''-10'' from the port. A step up to 1'' or even 1-1/4'' can help improve torque and top end breathing depending on the muffler. A straight through glasspack allows the engine to breathe better usually. Gives a nice tone as well.
     

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