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Thread: Cheap Exhaust

  1. #21
    Senior Member
    Bike: NC700X
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    Quote Originally Posted by Krampus View Post
    That's a fairly strong reaction to Jos' comment. What is it that leads you to believe it is not accurate or is invalid?
    4 stroke engine performance tuning is based upon pressure waves and exhaust geometry to increase engine performance. The classic reverse cone megaphone increases performance by first having a long increasing diameter cone with a short decreasing diameter cone at the end. When the exhaust valve open a pressure wave is created and when it travels to the long cone, the speed of the wave speeds up and creates a low pressure that helps to scavenge the exhaust gasses. When the pressure wave reaches the reverse cone reflects the pressure wave back up the exhaust to decrease the amount of fresh charge that would otherwise escape from the cylinder. Like a musical instrument it's tuned by its geometry to most strongly work at a single frequency. Reciprocating internal combustion engines are fundamentally air pumps and are most efficient when tuned to work at single speed/frequency. This is why vehicle automatic transmissions keep getting increasing numbers of gear ratios, or infinity variable ratio transmissions. This is also why variable pitch props were developed.

    So, when one changes the muffler only a part of the exhaust system is changing and it's not part of the tuned system. The tuned part of the exhaust is the header pipe out of the engine to the muffler. What the muffler does is disperse the energy in pressure waves in the exhaust. So long as the stock muffler doesn't restrict the bulk flow out of the exhaust, an after market muffler won't increase engine power. The NC engine has two other things that diminish the ability to tune the exhaust: the catalytic converter that disperses the energy in the pressure waves, and, just like the intake, the exhaust ports are siamesed in the head co-mingling the exhaust pressure waves.

    Design elements specific to the NC engine eliminate, or severely limit, the usual approaches to increasing engine power by changing the exhaust system.

  2. #22
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    When i bought my used '12 700x it came with an aftermarket Danmoto can. one of their cheap ones. it looked and sounded fine but developed a crack at a weld , so I bought another brand off Amazon. Think I paid $60 for it. You could run it full baffle. the baffle w/o plug, or no baffle. I liked the medium setting. I was pretty happy with it , but I sold the bike so I can't attest to the longevity.

    NICECNC Carbon Fiber Painted 1.5-2"Inlet Exhaust Muffler with Removable DB Killer for Street/Sport Motorcycles and Scooters with 38-51mm Diameter Exhaust Pipes

  3. #23
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    I used a long punch to make a 1 1/2 inch hole all the way down inside my stock muffler. It is a little louder so I can actually hear it now. Didn't cost anything.

  4. #24
    Senior Member Krampus's Avatar
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    Quote Originally Posted by b_rubenstein View Post
    4 stroke engine performance tuning is based upon pressure waves and exhaust geometry to increase engine performance. The classic reverse cone megaphone increases performance by first having a long increasing diameter cone with a short decreasing diameter cone at the end............................
    Very familiar discussion and examples: Reflecting On Exhaust Waves | Cycle World

    I think you both are saying the same thing: Exhaust is a tuned system based upon pressure waves, flow rates, etc. A non-engineered, or at least iteratively (trial & error testing) developed, muffler can and may make things worse rather than improve upon that system. Sport Rider showed this qualitatively in their OCT2004 issue where they tried 30 aftermarket mufflers on an R6. Smaller diameter pipes favor low-mid range tuning (street riding); larger diameter favor high end and forced induction (racing); length of pipe to include muffler core seems to play into this also, but it is beyond my understanding. I got an aftermarket muffler that was closest to stock system in length possible from a reputable mfgr; with dB killer installed throttle response at on-off transition is improved (opinion).

    This one seemed a decent primer on exhausts also: Tech: All About Exhaust Systems | MOTORCYCLIST

    Have to go riding now. Cheers.

  5. #25
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    Turns out that today Cycle World posted a Kevin Cameron video titled How Exhaust Pipes Work (no mention of mufflers).

    BTW, if anyone is interested in looking at Gordon Jennings Two-stroke Tuner's Handbook, that Kevin mentions, you can come by my house and take a look:

    Cheap Exhaust-2-stroke-tuners-handbook-jpg

  6. #26
    Junior Member
    Bike: NC700X
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    I put a cheap Dan Moto on mine and I can't tell any difference in performance either way. It mostly just makes it louder. Its still a ton quieter than most bikes though, even with an open exhaust.

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