<E36> '98 Muffler Mechanism?!?!?!?

[Bimmer <bimmer@xxxxxxxxxxxx>]

The '98 E36 323is comes equipped with a duel port muffler.  When following
behind my wife's E36, I noticed that the inner port on the muffler seemed
to be plugged.  My initial thought was that it seems pretty stupid to for
BMW to have "welded" another pipe onto the muffler, just so that the rear
muffler pipes could display "duel" chrome tips.  After allowing it to
bother me for a while, I decided to take a closer look.  I was a bit
shocked to find both ports were open.  Upon closer examination, I saw a
butterfly valve, located within the inner rear pipe, and a vacuum regulator
mechanism off to the right that controls the valve.

What is the purpose for this contraption, and how does this help the engine
management system?  Is this contraption used on other model BMW's?

It might be nice to post all responses on the digest so that others who
stick their noses into their mufflers in the near future will already know
what the muffler mechanism is for.

Regards.

Michael

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