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Expansion chambers (how they work)


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nsr250monkey

 
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Expansion chambers (how they work)

Wed Nov 02, 2005 7:34 pm » Post: #1 » Download Post

Guys,
Stumbled across an interesting site on expansion chambers and how they work, it even tells you how to make your own (double sided sticky tape not included !!)
http://www.froggy.se/skalmanmc/rd350/tuning/expan1.htm
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rc46

 
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Wed Nov 02, 2005 9:03 pm » Post: #2 » Download Post

if you think thats intresting, Buy the book.... blow yer mind. chamber shape head shape, porting, crankcase's, plug postion on and on and on and on... makes you think!
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Matt@TYGA
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Thu Nov 03, 2005 10:22 am » Post: #3 » Download Post

If only it was that simple.

The easiest bit of an expansion chamber is getting the tuned length somewhere near. This is controlled by exhaust port timing and exhaust gas temperature. Matching the rest of it up is the tricky bit.
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ahug030

 
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Thu Nov 03, 2005 8:34 pm » Post: #4 » Download Post

I think if you looked it up, you would find for a tube open at both ends the natural frequency of vibration is proportional to one over its length, more specifically f=nc/2L where 'n' is any number from 1 onwards and 'c' is the speed of sound. From this, the pipe would only resonate at engine speeds of f=c/2L,2c/2L,3c/2L etc. So I don't understand how a chamber could possibly be tuned to give a continuous increase in power (think about 'boy racers' - load exhausts become much louder at certain engine speeds). Say if you wanted the pipe to resonate at its fundamental frequency (n=1) at 7,000 rpm = 733 radians per second, the length of the chamber would be 0.226 m, which seems reasonable... but until you move to another speed at which resonance occurs, the chamber wouldn't have any benefit! Sorry I can't help it i'm an engineer... Embarassed
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ahug030

 
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Thu Nov 03, 2005 8:50 pm » Post: #5 » Download Post

Sorry 7000 rpm = 117 Hz, L = 1.4 m - this would be too long, but then again at 7000 rpm the vibration might be at the second or third natural frequency (n=2,3)...
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rc46

 
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Thu Nov 03, 2005 8:50 pm » Post: #6 » Download Post

Ah but do you work for honda LOL Very Happy they only get the best kind LOL Very Happy well the book i have which is the topic being discussed talks about diffrent shaped chambers and lenght for diffrent engine speeds at no point dose it say you can have a chamgber that dose it all, the chap who wrote the book said he had several chambers when he went racing some for wet conditions some for long circuits which need top end, and twisty tracks where you need more mid range, I guess the stuff we buy for our bikes is a happy medium. but make your own, no thanks ill get mine from Paul or Matt
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mick

 
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Thu Nov 03, 2005 9:26 pm » Post: #7 » Download Post

rc46 wrote: but make your own, no thanks ill get mine from Paul or Matt


i'm with you there mate Very Happy
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