After going through a credit card\Paypal dispute to crawl back some money from the ****s at Milian exhausts, i spotted a local guy on FB selling a M54B30 in 'limp mode' he had removed to do a LS swap. One of the first M54's made being a '99 build and came with a few goodies - a full M52\early M54 exhaust (minus the cats which someone had cut out), Dinan CAI (which i gave to @Vass as it was cut improperly on the side and filters are way overpriced) and TMS underdrive pulley kit (fitted)
Was tossing up using the M52 setup but no cats, crappy pipe work and me not wanting to polish another entire exhaust i decided to join the M52 downpipes on my existing system. Not a hard job right? turns out some muppet at BMW decided to use 2 different exhaust pipe diameters after the down pipes, never noticed them being different but on the E46 at least they are - ~45mm and ~50mm ID and ~1.5-2mm thick. To make matters even worse the M52 setup is double walled to the cats unlike my single walled system in the same section, i assume they did this to quiet it down a bit given the lack of primary cats.
After finding nothing locally i turned to Aliexpress which always delivers. I managed to get 51>50mm and 51>45mm pipe reducers which were a near perfect fitment. Obviously the 201? stainless quality and thickness isnt on the level as existing system, but i think it will hold up for my usage. No TIG currently available so trialed some SS 308 flux core. The stuff actually welds better than expected correctly positioning ie not upwards on axle stands, tidy enough for an exhaust and leak free but i may redo it properly with TIG and better steel if i can find the sizes.
After installing a new stud fitting the M52 headers was very easy, frees up quite a bit of room, less heat, half the weight and best of all you cant see the ugly cats now. Got M52 heatshield and another 990mm O2 sensor for the front bank in an attempt to route it the same as the rear bank, it mostly worked but was still slightly short so went along side the valve cover slot as opposed to in it. I dont know how exactly the M52 stock setup routes which would of been nice to know.
Sound wise they are noticeably deeper, like someone turned up bass a couple of notches. It has a small burble\resonance at 1.5-2k range when accelerating slowly but otherwise you'd assume it had an aftermarket muffler. Certainly wouldn't want it any louder given my car was already louder than what people say their stock E46 exhausts are, given the lack of sound deadening.
Performance wise it certainly feels like it pulls stronger, more noticeable in the ~5500+ range where most M54 start feel flat. Throttle response feels better too, maybe with the pulleys maybe adding a touch of help or just placebo. I do have various Draggy runs from summer 2023 on the old setup so will do some more in the future.