I know this has been done before a few times but just figured I'd share my experience with some pictures.
Parts used:
- OEM 335 axle back exhaust/muffler
- 335i rear bumper diffuser
- OEM BMW muffler clamp (for F30 328i - 75mm)
Since the 335 piping near the muffler is 5mm larger than the 328 we needed to add a small piece of piping to the muffler side of the piping in order to use the factory 328 clamp. It was a bit tricky to align the piping due to our initial cut not being in the ideal spot. This resulted in about 30 minutes of extra fabrication work but ended up working out fine. I suppose it would be much easier just to weld everything but I needed this to be reversible (I can reinstall the 328 muffler and rear diffuser in about 15 minutes).
Overall the car sounds MUCH better. Pretty loud during cold start, and has a nice rumble during idle and normal driving conditions but not too loud at all. I also have a catless downpipe installed which I'm sure adds to it a bit.