We picked up our MKV a couple weeks ago immediately threw on one of the EPA approved high-flow catted downpipes we've been testing for the B58 motors. After 600+ miles we still have no CEL without touching the ECU.
We also have a catless version available. Our catless downpipe starts at the 4.5" turbo flange, and tapers to the 3.5" flex section, and then down to the 80mm of the stock exhaust flange, so the diameter never shrinks under 80mm, even at the flex joint.
The next step was to build a full exhaust system. The stock MKV exhaust had typical BMW piping, starting at a decent 80mm but then tapering, flattenting, and pinching in some spots to create an abundance of clearance as it passed through chassis braces and the subframe. In the past, we've had great results using 3.5" on our M2/3/4 exhaust systems that are capable of 700+whp without any issues, so we pushed forward with the same material. The result was a straight 3.5" mandrel bent system from the downpipe all the way back to a Y-pipe we built at the rear. The Y would split between a muffler and a straight pipe. For those of you that aren't familiar with BMW exhaust systems, for the past decade or so they've all included a valve that opens and closes based on the driving mode and throttle position. Since we already build systems using this valve, we already had the castings completed and were able to implement the valve on the straight-pipe side. When the valve is open, exhaust gases can freely pass through both the muffled and open side, but when it's closed they are forced through the muffler for a quieter exhaust note. The entire system is made from TIG welded 304 stainless steel.
We were also hoping our B58 charge pipe would bolt up, but when we tried to install it we realized that the throttle body connection on the B58 in the MKV had a different flange. It now used a slide-in flange with an o-ring instead of a typical bolted flange. No problem, we drew it up and 3D printed it to test it, and it's now being cut out of aluminum by our local machine shop. So by next week we should have a MKV specific aluminum chargepipe that will allow easy methanol injector and not be susceptible to cracking like the stock plastic variant.
Once we had the airbox off we were able to get a great look at the new 2-port turbo design. Again, flanges have been drawn and are being cut already to begin work on a turbo manifold.