Expansion Chamber Resonance

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FreeWheeler

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Jun 22, 2010
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I get the idea that an expansion chamber gives a supercharging effect in a very narrow range when it resonates. If I understand it(questionable), the power band is narrow because the pipe hums at a specific frequency.

What I wonder, if I'm right about rough theory, is if the sound wave returning to the combustion chamber were variable and controllable, what would need to vary, frequency, intensity??? At what point in RPMs would certain frequency and/or intensity be best???
 
foureasy

foureasy

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Jul 9, 2009
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tucson
To change the rpm that the pipe "hits" you would need to change the distance from the piston skirt to the mean reflection point of the baffle cone. Shorter makes power higher and longer makes power lower. Other than putting a powervalve on it, the only thing you can change while running would be the pressure bleed, or "stinger". You would need some sort of valve. Not really worth the time.
Build your own pipe?
 
foureasy

foureasy

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Jul 9, 2009
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tucson
To change the rpm that the pipe "hits" you would need to change the distance from the piston skirt to the mean reflection point of the baffle cone. Shorter makes power higher and longer makes power lower. Other than putting a powervalve on it, the only thing you can change while running would be the pressure bleed, or "stinger". You would need some sort of valve. Not really worth the time.
Build your own pipe?
 
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FreeWheeler

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Jun 22, 2010
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I want to build a pipe. I found some software that's on sale for $14.00, was 50 some, optimizes and then prints out the templates. I probably should go for the hybrid engine, that would need a pipe as you have shown ol BMF foureasy. :D
 
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FreeWheeler

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Jun 22, 2010
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I'm playing with that pipe program and trying different guesses on the numbers for the stock chengine.

My guesses:

Exhaust port diameter: 25mm
Exhaust port depth: 25mm
Exhaust open duration: 150 degrees
Transfer open duration: 75 degrees
Target RPM: 5000 RPM
medium powerband

I must be way off on my guesses for the port durations because the pipe is huge in length and not much bigger in diameter anywhere than the stock header pipe. These are guesses because to pull the head voids warranty.

I'm going to fiddle with the cone program to see if I can make a paper pipe that goes around my bike frame.
 
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Frenkied

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Nov 4, 2010
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florida
Hey free wheeler you might not be that much off on the guessing because i aspoke to an local chamber builder and he told me in order to get the potentiel of the motor he showed me a pipe that's almost the same length as the rear fork from the crank back.Keep posting your findings.
 
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FreeWheeler

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Jun 22, 2010
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Maryland
Thanks for the encouragement.

I'm in the ballpark now, but without measuring the exhaust and transfer port duration it's still a guess. The pipe I came up with looks like those pocketbike pipes and is about 825 mm while the bike's crank to dropout length is about 700. I drew it out and looks realistic. Varying only the exhaust port diameter doesnt change the tuned length just the diameters.
 
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FreeWheeler

New Member
Jun 22, 2010
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I used the cone program and got out the scissors and tape. I believe this thing would scream if I built it. I still would have to figure out how to curl sheet metal and how to use cone to turn corners.

Here's the pipe without turns.
 

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FreeWheeler

New Member
Jun 22, 2010
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Maryland
I'm gonna try and make this pipe.

Is it possible to pound sheet metal around a form? I could make the forms by pouring epoxy and graphite powder into 1/2 diameter cones. Anyone?
 
Goat Herder

Goat Herder

Gutter Rider
Apr 28, 2008
6,237
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N.M.
I am confused and I have never tride making one of these. I seriously intend to though. Why cant a guy just bend these pieces in their hands. Perhaps against large sockets and the like.

Its just sheet metal.
 
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FreeWheeler

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Jun 22, 2010
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Hey guys, I dont know nuttin about metal working. Every mold I ever made was for fiberglass, but I'm thinking if the form is tough enough(epoxy and graphite) just beat the out of the sheet metal until it goes around and then weld the halves together sorta like stamping by hand.
 
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Black_Moons

New Member
Oct 25, 2010
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Canada, Bc
Mmmm, Look into hydroforming, I think thats how the bananna style expansion chambers are made. Real nice looking, And I think its started off just by welding the seams on two chunks of metal, and welding on a small inlet. Then its just a matter of filling with high pressure water. (or oil) A grease gun has been known to be able to pump up to 3000psi... Or any old hydraulic pump could do.. Maybe one of those 'porta-power' rams (hand operated hydraulic pump)

of course, this is just what little I have learned of it and you are best googleing for more information. Does not seem hard however. And the results look nice!
 
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FreeWheeler

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Jun 22, 2010
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Maryland
Interesting, I saw a video of it. I have a powerwasher, but the nozzle would have to come off I think so I could fit a different outlet. The cone program would come in handy to get the flattened out shape. I made a small paper cone tonight and read your post and then flattened the cone. This would be the flat shape of one half and when pumped up it should fill out.
 
retromike3

retromike3

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Jan 9, 2009
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Beaverton OR
The question is why build one if you can buy one for next to nothing? I got mine from Sick Bike Parts and although I had to modify it a bit It made a big difference right out of the box. I have been spending the time on other parts of my build. Why reinvent the wheel?

mike
 
Goat Herder

Goat Herder

Gutter Rider
Apr 28, 2008
6,237
20
38
N.M.
retromike3 said:
The question is why build one if you can buy one for next to nothing? I got mine from Sick Bike Parts and although I had to modify it a bit It made a big difference right out of the box. I have been spending the time on other parts of my build. Why reinvent the wheel?

mike
Click to expand...

For me I already got two of the SBP tuned pipes time for something different and more precise to my demands. How about when you can make one of these that wraps around a Custom build :D

How uber cool would that be?

http://i137.photobucket.com/albums/q208/foureasy/DSC01230.jpg
http://i137.photobucket.com/albums/q208/foureasy/DSC01231.jpg

I wind up posting links to this guy's pictures. I can't find any pictures of anybody else that's done it.
 
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FreeWheeler

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Jun 22, 2010
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Maryland
The more I think of hydroforming, the more it seems possible, even the turns in a pipe. Why order out when you have a stove and fridge?:D I'm only cooking for one at this point.

foureasy set a high example of what can be done.
 
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