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Tuesday, April 23, 2024

Doug's Domain

Doug Vetter, ATP/CFI

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Sunday, January 12, 2014

M3 Exhaust Installed

Okay, okay. I know what you want to hear so I'll jump ahead. I managed to replace the Stromung with the M3 exhaust today and the news is good. The exhaust is essentially as quiet as the non-M at most engine speeds, the drone and vibration are absolutely gone, and there's only the slightest increase in the exhaust note perceptible from the interior at lower RPMs typical of the M3 as it lacks a butterfly valve. The character of my BMW has been restored, I no longer have to drive around with a baseball cap on backwards to look the part, and my neighbors will no longer hear me approaching from two zip codes away. So I'll call this a resounding success.

Fortunately the installation went far faster than I thought it would and even with the need to wash & repack the Stromung for sale I was on my way home in two hours. All the copper nuts were loosened and removed easily, and I realized that I only needed to remove the two lower nuts on the mounting flanges that hold the muffler body to the hangars to release it. I used a milk crate and an assortment of folded towels to raise the muffler body up to the level required to mate the pipes with the midsection and sent it home.

I should point out that I'm glossing over the typical annoyances of this job, including the difficulty of inserting the smaller of the two sealing rings, which is not captive in any way (meaning, you have to hold it in place as you mate the pipes). Do this wrong and you'll either drop the sealing ring on the floor (as I did three times, sad to say), or pinch your fingers between the pipe flanges. I caught the very tip of my index finger between the pipes while installing the Stromung a few weeks ago and that hurt like a bitch. With the weight of the muffler body on the pipes it's difficult to rotate or move the pipes fore / aft so if you do pinch your finger, it can easily do damage as you wrestle in a panic to pull it out. So the moral of the story is keep your damn fingers away from the pipe flanges while you insert the smaller sealing ring. This is, of course, easier said than done.

I also encountered a couple problems -- first, the new sealing rings the parts guys sold me yesterday were the wrong parts for this application. I would have given the E46 some needed exercise and picked up the parts at the dealer but they weren't open today. For this reason I had to reuse the existing parts, but fortunately they appeared to be in good shape so I don't think I'm risking an exhaust leak by using them again.

The other issue I noticed is that the new copper nuts were 13mm, rather than 12mm. Given that the bolt heads are 13mm this presented a problem as I lacked two 13mm wrenches, and there's at least one bolt / nut that is inaccessible with a socket & ratchet. My solution? I used a 1/2" wrench I had on hand and it worked beautifully. The upside of these nuts is that the flats are bigger. That translates into more surface area so they may be less likely to round over under torque. Who knows...maybe the 12mm nuts were upgraded for this reason.

To wrap up the job I also had to drill a couple of small holes in the edge of the bumper cover / valance and diffuser to mate them with a ty-wrap so the diffuser wouldn't flop around in the breeze. No thanks to Stromung, of course.

To summarize, I'd recommend the M3 exhaust as an excellent upgrade for non-M owners, provided your vehicle has the requisite OBD2, twin-pipe midsection. It preserves the character of the vehicle while looking great. However, I'll reiterate that these parts appear to be in limited supply, and unless BMW orders another batch from their suppliers this option may not be available much longer. I suggest placing an order for the part even if they are not available in worldwide inventory, as this is the only way BMW knows what parts are in demand and whether they can justify another production run. The trick to this, of course, is not to wait until you absolutely need to replace your exhaust (my case) to order it. Plan ahead!

[Update: The Stromung has been sold.]

Mileage: 243975