Alright, a little update after the first track event after the build completed just a few weeks ago. I finally got the brackets I ordered on Friday afternoon and had them swapped out in about 20-30 minutes and got on the road up to VIR. I met up with my friend Andy who just got his M2 over the 1200 mile break-in period and had the Dinan intake and exhaust installed on the way and we convoyed up there. I kept having the same clunk and it was really not fun the whole way up, but only seemed to be apparent during slower speeds up to around 55 or so, but weren't bad around 80 or so where we were most of the way.
I wasn't able to take another look at it that night, but I did take a look at the bumper to see if anything plastic in there was shaking around and causing noises. I immediately noticed that the right side fog light was secured on the inside edge (with screws), but the outside part was flapping around like crazy. Removed the fog light and found the bracket that mounts to the bumper to hold the fog light had come off and was just sitting inside there. I pulled it out as well. I checked the other side and noticed that the alternator cooling duct (not used anymore) was loose and so I pulled that out as well, which unfortunately left the brake cooling duct loose, but I couldn't do anything about that at 10pm in the hotel parking lot, so I left it. In the morning on the way to the track, the clunking was still there. Ugh!
After borrowing a jack, jack stand and some tools from our neighbors, I found out the culprit. It turned out that the nut on the idler arm pivot bolt was loose and allowing the whole tie rod to slide around. At first I thought that I just didn't tighten it properly when building it, but now I'm not so sure. I got the bolt tightened up (only needed 35 lb-ft) and got it back on the ground, but now it had a loud popping when turning the wheel to the right and back. I concluded that it was likely a strut bearing going bad and we went ahead and did the track weekend. The car was fantastic all weekend. No more clunking and the car handled great, accelerated great, and just overall performed great. I didn't notice the popping at all on the track, just a couple times getting around the paddock. The brakes were still 530i brakes with OE pads, which showed their weakness very quickly. Brake fade was a big concern all weekend, so I wasn't able to go full throttle on the straights. I kept it under 120 MPH and mostly 110 MPH, since braking would suffer with any faster speeds. The car could easily go a lot faster though. I think 140+ would have been easily attainable if I had the braking confidence. I'll be putting the M5 brakes I have on soon, and I'll find some good track pads for the next event. I also hadn't replaced the rear struts with the M5 Konis yet, so it could probably have benefited from the stiffer suspension back there.
Once I got back home, I decided to get the car up in the air to take a better look. It turned out it was the ball joint on the center link on the passenger side rubbing the subframe. I was flabbergasted as to how that was possible. After a quick search, I found out that there is actually a way you can install the center link backwards (right to left), and it looked like I did just that. Unfortunately, it has worn through the boot pretty bad on the passenger side, so I'll need to order a new one and FCP should be able to refund me for the broken one. Since I'll be gone all week it should be in by the weekend when I can work on it after I get back.
I also finally got the bolts and everything I need to install the M5 torsion bars, so maybe next Sunday after I get the center link swapped, I'll do the subframe bushing replacement and install the bars.
Here's my car with Brian's M3T and M5T/SC that we built together:
My buddy's M2 in Long Beach Blue:
Another buddy's F10 M5 in Alpine White: