Thin-Data Summary
Most dependable: The B58 3.0‑litre straight‑six (440i) — widely regarded as one of BMW's most reliable modern engines and used by Toyota in the Supra — delivers 326 hp, effortless torque, and proven durability. The B48 2.0‑litre four‑cylinder (430i) is the pick of the four‑cylinder range, having solved the N20's timing chain issues. The N55 (435i) is a strong, reliable six‑cylinder option if well maintained. The early N20 (420i/428i) carries the highest risk — timing chain stretch and guide failure are well‑documented. The S55 (M4) is a proven high‑performance engine. Buyers should prioritise LCI models (2016 onwards) with B48 or B58 engines.









