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

["Mudry, Robert (CAP, AMR)" <rob.mudry@xxxxxxxxxxxxx>]

>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 is used on all OBD-II (96+) 328's and 323's.  It is supposedly there to
reduce exhaust noise in the low and mid rpm range.  The flap is closed at
idle and below 2500 rpm and opens above that point.  When the flap is closed
the exhaust flows thru the longer resonator pipe (it's kinda folded inside
the muffler like an intestine) reducing low frequency noises.  When the flap
opens, the exhaust flows thru the shorter pipe (straight through inside the
muffler) for improved performance.  If you disconnect the vacuum line the
flap will stay open and you will experience a rush of performance that was
previously missing.  At least 20 horses... <g>

>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.

Rob Mudry
BMW CCA #135536
'96 328is ...no flaps in my M3 exhaust :-)

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