Expansion Chamber Question

craiiiiiiig /
craigd
Feb 08, 2008 11:39PM

I was just read the Wikipedia article about expansion chamber exhaust and I had a question about something, this part here about the curves of the pipe:

"Expansion chambers almost always have turns and curves built into them to accommodate their fit within the engine bay. Gasses and waves do not behave in the same way when encountering turns. Waves travel by reflecting and spherical radiation. Turns causes a loss in the sharpness of the wave forms and therefore must be kept to a minimum to avoid unpredictable losses."

So with that in mind, that turns and curves cause losses in the sharpness of the wave, why would the Tecno Estoril have that huge bend in it that bends the stinger back over the pipe? I'm mainly curious about this after seeing an Estoril that had been cut and rewelded into a straighter position. Does this improve the performance of the pipe? Thoughts?

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Re: Expansion Chamber Question

warisesi /
Feb 08, 2008 11:44PM

the engine bay is very tight on a moped. the aftermarket pipes are a compromize for fit and function but function way better then stock piping

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Re: Expansion Chamber Question

Raymond Rexroad /
rarexro
Feb 09, 2008 12:11AM

The wiki article is talking about every part of the pipe EXCEPT the stinger shape. There really is little or no "wave action" in the stinger area. It is all in the body.

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Re: Expansion Chamber Question

peter /
peter
Feb 09, 2008 12:45AM

the estoril makes that bend AFTER the expansion chamber..

now, the proma circuit, thats the real question.

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Re: Expansion Chamber Question

Crackstar X /
crackstar
Feb 09, 2008 12:53AM

True, the stinger is only there as a pressure bleed, its been discussed tons. Especially on the IXII center bleed exhaust on rafters ridgid batavus/puch in breeding. As far as wave action diminishing due to curves and bends, when was the last time you saw any X games footage. The last time you perused a nasty ass dirt bike... those nasty huge one lungers have pipes with all kinds of bends in them to fit inside the chassis. but they still work. The sound wave is gonna go through the center of your expansion chamber just like your embouchure through a trumpet, how many more bends does a trumpet have. While at the same time mostly during the header pipe section of the pipe you want the cleanest exit for the exhaust gasses, after the header past where it expands thats the waves job not the pipes, What I mean with the header part stuff, is that ideally you want the exhaust gasses to exit with minimal resistance and then to expand and create a vacuum on the exhaust port, after that its all the "waves" responsibility

thats my view, it would make sense to have the whole system as straight as possible bt sometimes that isn't an option

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Re: Expansion Chamber Question

craiiiiiiig /
craigd
Feb 09, 2008 12:11PM

Thanks guys, thats super helpful. this is the bike I'm talking about, Devin's. I'm wondering how much of a difference cutting the pipe like that and rewelding makes?

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Re: Expansion Chamber Question

Shalerrr rrr /
shaler
Feb 09, 2008 12:14PM

it shouldnt make a huge difference because like peter said, its after the expansion chamber. i thought devin just did that for aesthetics.

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Re: Expansion Chamber Question

Bruce Edwards /
satoch
Feb 09, 2008 12:29PM

A smooth flowing header pipe is very important to performance. Length of the header is critical also.

A longer header provides more torque and a shorter header provides more top end.

In RC racing we swap headers and pipes frequently to "tune" the exhaust system to the track. By doing this we can adjust where the power band comes on.

Here's a great animation showing exactly what I mean:

http://www.bukupower.com/animateCorrect.html

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Re: Expansion Chamber Question

elliot /
elliot
Feb 09, 2008 02:18PM

stinger just lets the air out basically so it can be and shape, u want it as small as possable, but not so small it restricts hot gass flow outwards, then u will overheat (like clogged pipe)

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Re: Expansion Chamber Question

Bruce Edwards /
satoch
Feb 09, 2008 02:46PM

That's not exactly true. You want the stinger to be of large enough I.D. to allow as many CFM (cubic feet per minute) of air coming into the carb to exit thru the stinger.

You do not want it to be smaller as that will, as you said, choke the engine and cause excessive back pressure. That excessive back pressure will throw off the scavenging effect of the pipe and lead to an exhaust gases to remain in the cylinder and be mixed with the fresh incoming charge.

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Re: Expansion Chamber Question

WariSesi /
Feb 09, 2008 04:42PM

you want to tune the egt wif the stinger diameter so that you get even heat in the expansion chamber and find a balance so the heat is in the chamber and not blowing back into the cylinder. heat effects the speed of the shock wave more then the pressure but the pressure can be used to control the heat. usually you want to have the stinger in the 55-65% cross section area as the expansion chamber header.

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Re: Expansion Chamber Question

Steve /
47steve
Feb 09, 2008 08:49PM

If the bend is downstream of the chamber, it doesn't matter much, because all wave physics occurs between the two ends of the chamber and the exhaust port of the engine.

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Re: Expansion Chamber Question

Austin /
dirtyrottenstinkingbiker
Feb 09, 2008 08:58PM

the more restrictive the stinger the more power and heat the motor will make right?

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Re: Expansion Chamber Question

warisesi /
Feb 09, 2008 09:06PM

no the more stable the heat the more you can predict the speed of the reverberation the better you can tune it.

if you dont have head temperature gauge then make some inserts for the stinger and put some in to tune it wif the power band

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