WEIGHT: Between myself and @Nunga we figured out that the weight saving over OEM is around 2.5kgs. Roughly 9.5kg down to 7kg. NOISE: At idle, it is the same. Revving in neutral sounds slightly different. There is slightly more bass and the noise is more of a bark. While driving, again it sounds pretty similar. Didn't get a chance to fully open it up on the way home but the rasp is reduced a little and the volume is not noticeably different. On the whole it is not a particularly large difference, while it may have been just me, I couldn't help feeling like the system sounded a bit strangled, I am hoping that fitting the race back box (which is on the list for the future) will open up the exhaust and exaggerate the characteristics of the centre section. FITMENT: The fitment to the cats is simply 2x 3 nuts & bolts. Mine needed air chiseling out. I considered lowering the whole system from the front of the cats to the back box and cutting them out but the chiseling seemed to work pretty well in situ. I ordered new nuts and bolts from BMW. Once the clamps to the back box were undone, the centre section can be twisted to break the seal with the back box sleeved pipe and then angled down and slid out easily. However, upon re-installation, even after wire brushing and with 2 people it was proving difficult to get the sleeve back in, and given I still had yet to fit the X8R clamps I decided to remove the back box and mate the two together on the floor, using a fair bit of wiggling, the provided aftermarket seals, exhaust paste and some gentle encouragement from a rubber mallet. As you can see in picture 2, my second hand centre section came with two flanges and the wire seal already attached. These flanges presumably mate up to the SS back boxes perfectly, but as one of them cannot be removed due to the flare on the pipe, you would not be able to fit these to an OEM backbox without the X8R clamp. Or if you did you would have a flange rattling around. The 2 peice X8R clamps are exactly the same size as the Supersprint flanges, so instead of needing all eight, I only needed four, and the bolts ran through both and held them together. Unfortunately I didn't know I was going to write this so didn't get any pictures of this but the bolt set up is supposed to go "BOLT->WASHER->flange->flange->WASHER->SPRING WASHER->NUT". But the lack of taper on the Supersprint flanges means that you won't get the nut on with the washers. To remedy this I did up the nuts to tighten the clamps and then took them off and replaced after fitting the washers. When tightening the sleeved section, my old wire seal cracked, so I decided to start again with the provided new one. The bolts were done up just enough to allow a bit of flex, then it was all bolted back up at the back, then the central mounting bracket and cat bolts, before finally tightening the back box bolts once I was sure it was all aligned. I hope this will be of some use to people thinking of going down this route, if you would like to see more of my car, the build thread is here... https://forums.m3cutters.co.uk/threads/young-bens-silbergrau-e46-m3.212111/page-2#post-2806069 And if for some reason you have arrived here and need an OEM centre section, mine is currently for sale here... https://forums.m3cutters.co.uk/threads/e46-m3-oem-centre-section-with-gaskets-£60.215158/ Cheers.