Both are 3.0-litre turbocharged straight-sixes. Both are tuner legends. But if you're spending your own money on a used one rather than a project car, the gap between them is enormous — and it runs the wrong way from the hype. The N54 is the engine enthusiasts romanticise; the B58 is the one you actually want to own.
Quick answer: The B58 (89/100, BEST) is one of the finest petrol engines BMW has ever built — reliable enough that Toyota put it in the Supra. The N54 (42/100, AVOID) is a thrilling but fragile pioneer: a critical fuel-pump fault plus expensive injector and turbo failures. Buy the B58 unless you're going in eyes-open for a tuning project.
The pioneer that broke
N54 — 42/100 (AVOID)
BMW's first mass-market turbo petrol six (2006–2010) was a monster for its time — and a maintenance sinkhole. The failure list reads like a horror story — one critical item and two expensive high-severity ones:
| Problem | Severity | Repair cost |
|---|---|---|
| High-pressure fuel pump (HPFP) failure | Critical | €920–1,380 |
| Turbocharger failure (one or both) | High | €1,660–6,270 |
| Piezoelectric injector failure (×6) | High | €1,520–4,780 |
| Wastegate rattle / actuator failure | Moderate | €140–830 |
The HPFP was so common BMW recalled US cars and extended the warranty there (not in Europe). Stack turbos, injectors and pump together and a "cheap" 335i becomes a five-figure ownership risk. The N54 is fast and tunable — but the reliability record is genuinely poor.
Found in: BMW 135i, 335i, 535i, Z4 sDrive35i (2006–2010).
The icon that didn't
B58 — 89/100 (BEST)
Two generations later, BMW got it completely right. The B58 (2015→) makes more power than the N54 ever did in stock form, yet its faults are mostly bolt-on parts:
| Problem | Severity | Repair cost |
|---|---|---|
| Oil pump plastic ring cracks — oil pressure loss (2018–2022 engines) | High | €1,100–5,500 |
| PCV diaphragm in the valve cover / valve cover gasket — oil smoke, leaks | Moderate | €920–2,350 |
| Coolant loss — expansion tank or cap, electric water pump | Moderate | — |
| Plastic charge pipe crack | Minor | €80–200 |
Nothing critical. The one item worth checking is the oil pump on 2018–2022 engines, where a plastic ring can crack (later engines got a metal ring); BMW also extended the PCV-valve warranty in the US. This is a top-of-the-table petrol engine that happens to also be a tuner's dream — Toyota's confidence in it for the GR Supra says everything.
Found in: BMW 340i, 440i, 540i, M240i, M340i, X3 M40i, Z4 M40i — and the Toyota GR Supra.
The 47-point gap
| N54 | B58 | |
|---|---|---|
| Era | 2006–2010 | 2015→ |
| Power (stock) | ~306 hp | ~387 hp |
| Score | 42/100 | 89/100 |
| Critical faults | 1 | 0 |
The verdict
Same layout, same "tuner six" reputation — but the B58 is a different universe of reliability. If you want a fast BMW six to own and enjoy, the B58 is one of the safest performance engines on the market. The N54 is for people who go in knowing they'll rebuild turbos, pumps and injectors — and who love it anyway.
For the generation between these two, see N55 vs B58, and for the diesel side of BMW's six, B57 vs M57.
Scores are calculated from documented issues, repair costs, and failure patterns. Reviewed by the EngineScope editorial team. Methodology →