X3M Competition S58 — stage 1 tune results and daily drivability review

Running a tuned X3M Competition as well. I went with MHD stage 1+ on 98 octane and the results are similar to yours. The S58 is a beast of an engine — the closed deck block and forged crank mean the bottom end can handle significantly more power than stock.

For stage 2, the catless downpipe makes a huge difference on the S58. The stock cats are very restrictive and removing them frees up a lot of exhaust flow. Expect another 30-40hp on top of stage 1. VRSF and Eventuri both make quality downpipes for the S58.

One thing to watch — the S58 runs very hot under sustained load. An upgraded intercooler is worth considering if you do track days or spirited driving in warm weather. The stock intercooler heat soaks quickly.

The S58 at stage 2 with a catless downpipe and upgraded intercooler is making 620-650hp on some dyno sheets I have seen. That is supercar territory from a compact SUV. The xDrive system handles it well but you will want to upgrade the rear diff fluid to something with higher thermal capacity if you track it.

For warranty concerns — any ECU tune will void your powertrain warranty if BMW detects it. BM3 has a feature to flash back to stock before dealer visits, but BMW can sometimes detect that the ECU has been modified even after reflashing. Just something to be aware of.