X4 M40i B58 — same engine as M340i, same tuning potential?
The X4 M40i shares the B58 engine with the M340i, M240i, and Z4 M40i. Stock output is 382hp and 500Nm. But does it tune the same as the sedan?
I had my X4 M40i tuned with BM3 stage 2 (catless downpipe + tune on 98 octane). Dyno results:
- Stock: 348whp / 472Nm at the wheels
- Stage 2: 428whp / 612Nm at the wheels
That is an 80whp gain from a downpipe and tune. The B58 is an incredible engine for tuning — the stock internals handle stage 2 power without any issues.
The X4 is heavier than the M340i by about 100kg, so it is slightly slower in a straight line. But the higher seating position and xDrive traction make it feel very planted and confidence-inspiring.
The catless downpipe does produce a check engine light. I am running a BM3 map with the CEL coded out. No issues with emissions testing in my country.
For anyone considering an X4 M40i — the B58 tuning potential makes it a seriously fast SUV for relatively little money.
