Re: M6 Muffler Replacement (archive)

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I've researched this issue quite extensively over the past few months since I have the same car and Pennsylvania is changing it's emissions laws. The following presumes that your car does NOT have a cat and the emissions loop that was originally put on the car during federalization when it entered the country.

My car is an '85 M635 that was de-federalized (like most others) after import due to the generally poor quality of the conversions performed at EPA/DOT approved centers. There is a good article in the Tech section of this month's Bimmer Magazine about this exact issue.

The current configuration of my car has the headers going into a straight pipe that goes to a very long (about 3-4 foot) thin resonator, then a bent pipe, and then the stock euro muffler. None of these EOM euro components, from the headers all the way back to the muffler, are shared with the American M6. In fact, the American M6 doesn't even have headers, it has a manifold. So inserting a cat and a new muffler is going to involve end-to-end custom fabrication. Incidentally, the euro muffler is a damn good, pretty free flowing muffler, and the only good reason to replace it with stainless is for looks and longevity.

To make matters worse, the emissions loop that was fitted to federalized euro M635's was notoriously bad, and is difficult if not impossible to attain if it has been removed from your car. Even if you could easily fit a cat to your car, it would be destroyed in a year or two if your car was not tuned perfectly for driving under all conditions, which is near impossible. To add insult to injury, if you want EPA/DOT approval you will need to install original federalization equipment parts, even though contemporary systems might be superior. And those parts are, as mentioned, almost impossible to find. Nice Catch-22.

So you are left with the prospect of also including a track pipe in your fabrication process. But even with the Cat (and no emissions loop), there is a good chance your car won't pass emissions testing if your state uses the treadmill test.

I have talked to several mechanics who specialize in older, euro BMWs, and their concensus opinion is that I should do everything possible to avoid installing a cat on my car. My one saving grace is that Pennsylvania offers "Classic" plates to owners of unusual cars aged 15 years and over (versus designation as "Antique" which is 25 years or older). Classic plates are permanent, and excuse the car from emissions testing. The one drawback is that the car cannot be "used daily". There is also a weird loophole in Pennsylvania in which if the car fails emissions testing three times and has the original emissions equipment, it passes automatically with a fine. However, this process would cost you about $270/year every year. I assume most states have a similar clause.

: I am also looking for a muffler and catalytic converter for my '85 M635. Any leads???

: : Does anyone know of a Stainless Steel alternate to the BMW OEM muffler replacement? I do not want a loud muffler like the B&B Tri-Flo. Want to keep fairly close to stock sound.

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