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Discussion Starter · #1 ·
My 81 CX500 handbook refers to this as the Power Chamber.

Exactly what is this device. Is it really a power chamber? Is it an expansion chamber? Is it just a way to quiet the exhaust pulses?

Mine is in great shape, and I at this point I am satisfied with the quiet ride. But, my tailpieces/mufflers/baffles are showing signs of burn through near some of the welds in back. I am just thinking down the road, if I need to replace them what the role of that Power Chamber is exactly.



Scott
 

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Without getting into too much detail, it involves Bernoulli's principle, venturi and reversion effects. The "H box" directs the exhaust gasses in such a way that the exhaust pulse from one cylinder creates negative pressure on the other exhaust pipe and aids with extracting exhaust gasses from the cylinders.

If you've ever noticed that blowing across the top of a straw in a drink causes the drink to rise up the straw, you know what's happening.

And there's some sound deadening material in there too. ;)
 

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Discussion Starter · #3 ·
Okay.

I recently explored the Venturi effect on a Mercury Maurader 410Cu In V-8 in My '67. The Carb I had on the engine was a good runner, but it didn't quite perform as well as I thought it should. After a series of Jets and Rod, I finally figured out the Culprit. Mr. Venturi. There is an Audible difference in the sound of the motor breathing in (Exhaust sound isn't even included in this equation)

So, I believe the concept is referred to as "Scavenging Effect"
I wonder how much back pressure is needed to maintain this Scavenging effect/performance, and what is its effect on Volume.
 

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Here is a cutaway (sorry for the image size) showing the basic internals.



And here is a diagram showing a bit more detail of construction. Abe's info is pretty spot on.



Joel in the Couve
 

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I get a nervous twitch when people talk about needing back pressure.
Back pressure is when your exhaust cannot flow as fast as the gases want to and build up behind the source of restriction.
All back pressure is bad.

But, do not confuse back pressure with the resonance of sonic wave from combustion.
The idea is to tune the exhaust so the sonic waves rebounds off the back of the exhaust valve just as it opens, thereby helping suck the combustion gases out.
That is what cause the scavenge effect, Helmholtz:
Helmholtz resonance - Wikipedia, the free encyclopedia
 

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A lot of members are using practically new Harley mufflers that were removed by Harley owners who wanted obnoxiously louder pipes cause they "save lives"
 
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