I've got an E46 330 that is slowly morphing into a track car, but needs to remain streetable for the time being (driving to/from the track, occasional weekend fun drives). It's currently sans-catalytic converter thanks to aftermarket headers (swapped in before my ownership) as these cars have the cats integrated into the manifolds.
Goal: re-cat the exhaust to address the smell and (hopefully) allow it to pass VA state safety inspection, keep the sound & drone quiet enough for 2-3 hour drives to the track, and allow enough of that sweet straight six sound through to enjoy my sessions while I'm there.
As I haven't had much luck finding factory manifolds, I figured the easiest way to do this was to replace the forward resonator with a set of cats. Poking around online, it seems that E36's have the cats in that exact spot, so I picked up a set from M3 with the hope that it would be relatively easy to fit.
For reference, I have a mig welder and I'm capable of joining up the relatively thick OEM pipes. Otherwise I don't have any real exhaust fabrication knowledge, experience, or talent (hence the post).
Ok, here's the current state, the OEM exhaust (headers back) on top, with the E36 catted mid pipes on the bottom.
E36 header to cats:
E46 header to forward resonator:
Photo dump of how they line up for reference:
The good news is that the center sections line up quite well, so this has some promise, although there's some work to be done.
Questions for the hive:
Header end - cut/weld to adapt the E36 mid section to the E46 headers or source a set of S52 manifolds & bolt them up? The car may live a future life in spec E46 (which runs S52 manifolds), but that would require spending the time & money sourcing a set, plus replacing manifolds/headers doesn't look like a fun endeavor. I think adapting to the E46 headers is probably a better route.
Post-cat - My main goal is to minimize drone, this is where I need some help. After the E36 cats there is a set of resonators, if I cut here and adapt to the back half of the E46 exhaust, there would be two resonators (E36 front and the back E46 resonator). Alternately I can cut post-cats and only have the downstream E46 resonator. After this, I have the option of the factory E46 muffler or a no name E46 muffler that I pulled off as the drone was unbearable. Should I expect the cats to make a measurable difference in noise?
Overall, I'm inclined to splice in the cats & resonator from the E36 as that's the easiest route, cutting between the cats & resonators looks like it might be complicated from the stampings.
Finally there's the O2 sensors. I think they'll need a 90 so they don't come in contact with the body, but I'll worry that later.
