Overview
The headline improvements
The B58 closed the N54’s HPFP failure mode by redesigning the high-pressure fuel pump and the fuel injector geometry. The N55’s HPFP was more reliable than the N54’s but still had known issues at very high mileage; the B58’s HPFP is the next iteration of that design. Result: B58 cars are routinely run past 100k miles without HPFP replacement.
Block architecture
The B58 is closed-deck; the N55 is open-deck. A closed-deck block supports higher cylinder pressures and is more resistant to cylinder-bore distortion at high boost. Aftermarket: the B58 has more headroom for big-turbo builds because the block is stronger.
Stock power
N55 stock: 300–320 hp depending on tune and chassis. B58 stock: 320–382 hp depending on tune and chassis (B58 in the Supra is 382 hp; B58 in the G20 M340i is 382 hp; the G80 M3 S58 variant is 473 hp and is a different engine). The B58 has more standard-power headroom out of the crate.
Tuning headroom
Both engines have strong aftermarket support. Stage 1 tunes: similar gains (40–60 hp). Stage 2 (downpipe + charge pipe + tune): N55 makes 380–420 hp reliably; B58 makes 420–480 hp reliably. Stage 3+ (big turbo, built motor): both engines support 600+ hp with internal work.
Common faults compared
N55: VANOS solenoid clogging, charge-pipe separation (the OEM plastic pipe can’t hold boost long-term), ignition coil failures on early production, oil filter housing gasket leak. B58: VANOS solenoid clogging (less common than N55, same fix), the vacuum pump (introduced for emissions reasons) can leak; thermostat housing has been an issue on early B58 production. Neither engine has the N54’s index-12 injector failure or HPFP failure pattern.
The upgrade question
If you’re choosing between a used N55 335i and a used B58 M340i of similar mileage and condition, the B58 is the better choice for long-term reliability and tuning headroom. The N55 is the better choice for cheap entry into the platform — the cars are well-documented, parts are cheap, and the engine is forgiving of tune issues.
FAQ
Is the B58 more reliable than the N55?
Yes, in the headline ways. The B58 closed the N54’s HPFP failure mode (which the N55 was mostly immune to); the B58 also redesigned the VANOS solenoid (less clogging) and the cooling system. The N55 is reliable; the B58 is more reliable.
Can I make more power on the B58?
Yes. The B58’s closed-deck block supports higher cylinder pressures. Stage 2 tunes regularly see 420–480 hp; Stage 3+ builds go much higher. The N55 is limited by the open-deck block; very-high-power builds are rare.
Is the N55 still a good buy in 2026?
Yes. The N55 platform is well-documented, parts are cheap, the engine is forgiving of tune issues. A clean N55 335i at 80k miles is a strong buy. The B58 is the better long-term platform but costs more upfront.
Is the B58 the same as the S58 in the M3/M4?
No. The S58 is a different engine: stronger block, different head, twin turbo (the B58 is single twin-scroll). The S58 is the M version; the B58 is the road-car version.