4-stroke eng. exhaust pipe chamber (?)

[Artsi]

I spotted an additional exhaust runner resonance chamber on BMW 450cc motocross bike engine, see provided link.

I have tried to wrap my head around the design function of said chamber with no results. This does not seem to be an anti-reversion chamber.

I have however seen similar chambers on 4-cylinder naturally aspirated rally car engines. Chambers are there to even out torque curve. They're connecting cylinders 1-2 together, and 3-4 together (if my memory serves me right).

Would this BMW factory racing exhaust chamber serve same function?

http://juhasalminen.pictures.fi/kuv...ion, Finland, Feb (MP 2009)/7H1B2179.jpg/full

http://juhasalminen.pictures.fi/kuv...ion, Finland, Feb (MP 2009)/7H1B1989.jpg/full

 

[Deltona]

I have absolutely no idea what we are supposed to be looking at! Can you explain more and put some arrows on the pics?

 

[Artsi]

Here's a pic of the said chamber circulated in red. I hope this clarifies the location of the hidden chamber.

Please follow the link below, and while on the picture hosting site, click "VIEW FULL SIZE" -option (located on top right corner).

 

[Artsi]

http://image68.webshots.com/468/9/18/18/2508918180085019242emHwmL_ph.jpg

 

[Junior37c]

My understanding from having run some simulations on those MX motors is that it's just there to smoothen the resonance action across the RPM band. Smoothen out the power delivery.

 

[Swissscf]

This is a derivative of the FMF PowerBomb style chamber. Typically FMF is claiming a smoother/stronger boost in the low rpm powerband. They also say that there is a 1-2 dB reduction in the exhaust level.

Swiss