Hello,
I just wanted to share my experience on the addition of the down pipe for my X1 35i xi. So here is the highlights.
1. Installation took about 2 hours at my independent mechanic garage. He had a lift and all the tools needed to do the job.
The original catalytic converter is attached to the turbo, and it was replaced with a VRSF brand down pipe (DP). The Cat was a bit tricky to get out since there is a ring/bracket that holds it in place against the turbo. The DP is later reattached using the same ring.
2. before removing the cat, the oxygen sensors need to be disconnected from the engine bay connection, under the air intake piping(passenger side). It took a little while to find the connectors since there is not a lot of information online for that so check out the pictures. Also the exhaust needs to be removed from the cat area via bolts on the catalytic.
3. Once the cat was removed the oxygen sensors had to be removed from the catalytic itself. The lower one (post Catalytic) broke from the threads striping out its own threads. so only the pre cat oxygen sensor got re-installed in the DP.
3. since the DP doesn't have a catalytic converter the engine trows a code immediately, so i will have to deal with that, maybe by installing the JB4, which eliminates the code, supposedly.
4. The results are worth the trouble IMO. The sound improves drastically and the turbo spools more freely and the engine becomes a lot more responsive to the gas pedal. Even the sightless touch to the gas pedal allows the turbo to work more easily.
If you are thinking on doing this mod, I do encourage you to try it out (at your discretion, especially if your warranty is still covering you) But performance wise will clearly be improved.