Different(ial) Strokes

Different(ial) Strokes

Today is our penultimate post for Nick’s M3. We’ve got a lot to cover before the dyno tomorrow, so let’s get to it.

When we last left the M3, it was awaiting the final placement of the cutout, along with the exhaust tips. The first step in placing the cutout is, obviously, finding a place it will fit. It needs a decent amount of room, and since we had to place it after the second resonator (for the best sound possible while still retaining volume), we didn’t have too many spaces. Thankfully, the area right before the Y-pipe to the muffler had a good chunk of room available, so we marked up the pipe in preparation for some cutting and welding.


And a little bit of cutting and welding happened.


After that, we fabricated a larger tip for the cutout’s dump, and welded that bad boy into place as well.


And for the midsection, that’s all she wrote. Before we put it back up into the car, we set about taking a couple snaps of the whole system as it laid near the fan to help the cutout’s welds cool down.


But putting together an electric cutout system isn’t that easy. Oh, no. There’s also everybody’s favorite activity — soldering and running wires! Nick wanted his cutout switch placed somewhere stealthy, so we found the best spot that would hold the switch without interfering with other systems in the vehicle. We won’t say specifically where we put it, but the picture’s pretty much a straight-up giveaway anyhow.


Next, we had to fabricate the tips. Nick wanted a style similar to his old Eisenmann muffler, so we special-ordered some 3.25″ stainless steel and set to work. First, however, some eccentric rings had to be cut. We have them featured below in a picture. Basically, the E46 M3’s exhaust tips (the real ones coming from the muffler) are too close together on the OEM muffler to fit 3.25″ pipes next to each other. For that reason, the eccentrics are cut, which allow us to space out the tips left-to-right to fit within the cavity on the diffuser.


With a bit more welding, boom, more tips than the hottest server in the restaurant. The rear diffuser is still off, since his Vorsteiner one has some battle damage, and he’ll be bringing in the OEM replacement tomorrow.


We also gold-wrapped the corner of his trunk floor where the cutout is, to keep excess heat from potentially affecting the plastic in that spot.


With all the exhaust work done and awaiting road testing, we added the last bit of work to be done at the shop — his OEM BMW Motorsport 4.10 ring and pinion gear set. Here’s the old, boring differential gear removed from the housing. Jeez, just look at how boring it is, just sitting there not doing anything. Damn lazy-ass differentials.


Which is why we’re replacing it with the new hotness in the form of an OEM Motorsport replacement. If there’s one thing that never looks bad in a photo, it’s a set of gears (or turbine wheels) cut from billet.


Since it was the OEM Motorsport ring and pinion gear set, we assumed that shimming would only be a possibility, if not a non-issue. Thankfully our wishes came true, and the gears went in, and the differential went back together without issue. No shimming or other nonsense necessary. It’s our favorite kind of gearing swap — the easy one! After some sealant to put it back together, it’s going up into the car and will be test-driven to ensure proper functionality. We’ll have a picture and hopefully some video tomorrow, once Nick comes through with his Evolve-R tuner and we run it on the dyno. Get excited!!


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