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Guest Message by DevFuse

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expansion chamber ??

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7 replies to this topic

#1 ferp420


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Posted 04 December 2012 - 10:20 AM

I was just wondering if anybody's ever tried using a expansion chamber on the exhaust side as a performance upgrade I know they use them on 2 strokes bikes but I'm also starting to see them on the hi end 4 stroke race bikes our motors being so close to a motorcycle just wondering if it would give us any more punch any exhaust gurus out there with some insight ?

#2 Hatchback Lou

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Posted 04 December 2012 - 09:49 PM

bump. I'd like to know as well!

#3 zukiru



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Posted 04 December 2012 - 10:00 PM

expansion chambers on 4 stroke bikes are done to enhance the sound
. They don't work for adding horsepower to a 4 stroke engine as far as I know.

#4 Hatchback Lou

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Posted 04 December 2012 - 11:25 PM

Thanks! Thats kind of what I was thinking, but i don't know much about exhausts or bikes. Or bike exhausts.

#5 86 Wonder Wedge

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Posted 04 December 2012 - 11:41 PM

Well, expansion chambers are really meant to "backfeed" a pressure wave back to the combustion chamber to create a sort of valve to keep the new stuff from exiting the exhaust side, essentially turning it into a 4 stroke. :clap:

On 4 strokes (systems with valves, lol) bouncing back the pressure wave/stalling the gases exiting doesn't help when there is a valve in a way... lol

#6 ferp420


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Posted 05 December 2012 - 01:38 AM

heres a link to fmf racings powerbomb pipe http://www.fmfracing.com/Products/MX/44
what would %10 do for out little motors i know it would cost a fortune to make one for our cars fmf has been making pipes for along time and can spend the money and time on r&d doing that for a little old subaru would fall under the catagory of wtf dude why it sure would be nice though

#7 cubastreet


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Posted 05 December 2012 - 02:36 AM

an expansion chamber first returns a negative pressure wave that helps draw out exhaust gases and also helps pull up the fresh charge from the crankcase. Some of the fresh charge is often also sucked out the exhaust port

It then returns a positive pressure wave that stuffs the charce back onto the cylinder just before the port closes, giving a supercharging effect.

The pressure waves travel at the speed of sound, so this supercharging effect normally happens over a fairly narrow rev range, giving the famous 2 stroke powerband.

It doesn't turn it into a 4 stroke, the engine still fires once every revolution.

You could probably set up a single baffle cone to aid in extraction of exhaust gases but you'd really need one per cylinder which isn't really feasible with siamese exhausts.

#8 coxy


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Posted 20 December 2012 - 05:49 AM

FMF Powerbomb pipes are a real mongrel to jet on the dyno compared to a normal pipe so I wouldn't want one on a car engine.

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