BMW stands at the forefront of fusing high performance engines with everyday usability. And two of their finest examples come in the form of the N55 and B58 – 3.0L twin turbo straight six marvels.
These prestigious powerplants blend mammoth power with sophistication and precision craftsmanship worthy of BMW‘s blue and white roundel. But beyond their silken delivery of refinement resides intricately engineered masterpieces that bear deeper comparison.
Let‘s examine what really separates (and unites) these Bavarian mechanical icons!
The Art of the Turbocharged Inline Six
Before scrutinizing differences, it pays to understand what grants the N55 and B58 such illustrious reputations from the BMW faithful.
In a word – flawless execution.
BMW enjoys near mystical levels of praise for their smooth inline six magic carpets. And the turbocharged era only elevates expectations. Add the context of increasingly strict emissions and fuel efficiency regulations, and you have a fine line to walk.
Somehow both these engines manage to traverse that tightrope of opposition with poise and prowess.
The N55 glides in as a torchbearer – channeling BMW’s heritage for high-tech six cylinder symphonies into the 21st century.
The B58 follows, rebuilt from the studs up with bleeding-edge tech to set towering new expectations of power.
To most observers, these engines almost seem otherworldly in how they balance conflicting demands. Until you examine what lies beneath…
By the Numbers: Key Specs
First, let’s crystallize the nuts and bolts on paper:
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| Specification | N55 | B58 |
|---|---|---|
| Displacement | 2,979 cc | 2,998 cc |
| Layout | DOHC 24 Valve Inline-6 | DOHC 24 Valve Inline-6 |
| Bore x Stroke | 89 mm x 84 mm | 82 mm x 94.6 mm |
| Compression Ratio | 10.2:1 | 11:1 |
| Max Power | 306 hp @ 5,800 RPM | 382 hp @ 5,800 RPM |
| Max Torque | 295 lb-ft @ 1,200-5,000 RPM | 369 lb-ft @ 1,850-5,500 RPM |
| Cylinder Block | Aluminum w/ Cast Iron Liners | Aluminum w/ Iron Coating |
| Turbocharger | Single-Scroll TwinPower | Twin-Scroll TwinPower |
| Weight | 150 kg (dry) | 110 kg |
| Efficiency (EU Cycle) | 24.6 mpg | 32.5 mpg |
Gazing at the spec sheet dispels any notions of the B58 representing a gentle evolution. The newcomer arrives packing serious heat!
Jump past the familiar 3.0 liter displacement, and the B58 swiftly sets its own pace. A unique bore and stroke design unleashes a monumental 500 Nm torque crest – a 71 lb-ft advantage over the N55’s no slouch peak.
The B58 backs this brawn with 11:1 compression wizardry compared to the 10.2:1 squeeze of its elder. Output rises to a Porsche-pouncing 382 hp, while components slim down to fighting weight.
From turbo design to fuel injection advancements, this engine channels serious innovation to vault BMW another level higher. The efficiency figures speak for themselves – a 32% economy gain stands as progress no one expected.
Now to examine what choices drove this impressive performance…
Under the Skin – Key Architectural Differences
Pop the hood on both powerplants, and you’ll spot several key packaging revisions:
Oil filter housing – The N55’s Achilles’ heel comes from its oil filter housing placement, which commonly leaks fluid onto adjacent components when the gasket fails. BMW repositions the housing farther away from trouble in the B58.
Cylinder bore coating – In search of lighter weight and longer-term durability, the B58 abandons old-school cast iron cylinder liners. In their place sits an advanced Plasma Wire arc-spray coating applied to the aluminum block. Tests indicate superb thermal dynamics and friction reduction.
Consolidated intake – The N55 relies on twin intake plenums feeding each cylinder bank through long, intertwined tracts. BMW consolidates these to a single, larger plenum upfront in the B58. This straightens intake flow considerably for performance.
Water-air intercooler – Engineered for efficiency with maximum power delivery, a new water-air intercooler on the B58 optimizes incoming air temperature. This increases total airflow and ensures denser mixtures.
Lower turbo position – In the quest for compact dimensions without sacrificing smoothness, the B58’s turbo nestles deeply in the vee rather than sitting higher atop the engine. This centralizes mass while allowing efficient exhaust pulses.
Fuel injection – While both engines employ direct injection, the B58 gains BMW’s new stratified charge capability. By spraying fuel in stages, this significantly improves part-throttle response and emissions.
Combined, these updates create tangible impacts evidenced from behind the wheel. But comparing real world reliability and tuning potential paints a clearer picture…
Ownership Realities – Reliability, Power Delivery & Tuning
For most buyers, imagery of redlined tachometers or blazing 0-60 times melts away next to practical matters of daily driving. How do these legendary six cylinder engines fare on the upkeep and enjoyment fronts?
Reliability
+ N55 – Well above average when maintained; oil leaks and fuel pump failures stand out
Despite its overall strong service record, the N55 does suffer two Achilles’ heels related to premature failures:
-
Oil filter housing gasket – A notorious design flaw causes this seal to wear quickly from heat and vibration, allowing leaks onto the serpentine belt below. BMW eventually revised the part, but not before years of complaints.
-
High pressure fuel pump issues – Pre-2011 N55 engines came equipped with faulty direct injection fuel pumps prone to early failure. BMW extended the warranty as a result.
+ B58 – Too early to tell; engine still too new for longevity gauging
Thus far, no systemic weaknesses or problem areas have consistently plagued the B58. As BMW’s newest turbo six however, only time will tell just how durable under the extreme stresses of daily driving.
Power Delivery
+ N55 – Extremely broad torque curve; pile-driving mid-range; smooth turbo sans lag
Despite mild low-RPM turbo lag, the N55’s cardiovascular-level mid range punch stands out as a benchmark. The engine pulls hard past 4,000 RPM straight through to redline, aided by clever twin-scroll turbo geometry. Expect silken thrust with minimal fuss.
+ B58 – Ubiquitous torque across entire band; seriously quick spool; high RPM efficacy
Simply put, the B58 outpunches its elder thanks to sheer torque quantity and lightning fast boost response. Splashed across nearly 4,000 RPM, 500 Nm of twist vaults forwards with almost no lag before a scintillating surge towards peak power. Drivers can ride this wave or aggressively stab for even quicker response.
Tuning Potential
+ N55 – Legendary; capable of 800+ hp; huge aftermarket support
The N55 holds a vaunted spot in tuning circles thanks to immense headroom. Bolting on aggressive tunes and further fueling/breathing modifications can easily uncork 500+ horsepower. With built internals and auxiliary gear, 800+ becomes attainable even on otherwise stock engines.
+ B58 – Early traction thanks to robust architecture; capability still developing
Although the B58 remains in relative infancy for aftermarket upgrades, its stout design (forged crank/rods, supplemental cooling capability) lends naturally to adding power. Early tunes and bolt-ons effortlessly breathe life past 450 horses. As knowledge accumulates, the B58’s higher compression and advanced injection system may touch even loftier heights.
Eye to Eye: N55 vs B58 Verdict
When scrutinizing these mechanical masterpieces side-by-side, a familiar pattern emerges that plays out across BMW’s storied history.
The newcomer B58 clearly defines itself as a leap ahead versus the venerable N55. This goes beyond just benchmarks or specifications to reflect holistically in signature BMW character.
But does that relegate the elder statesmen N55 to obsolescence? Hardly.
In the same way an E46 M3 retains soul-stirring appeal next to BMW’s latest M4, the N55 stands immortalized by its irresistible blend of usable power and harmonic six cylinder soundtrack. There exists an unquantifiable mystique still cloaking the N55 that near-perfection from successors struggles to shatter.
Ultimately, both engines cement well-deserved places securing BMW’s prominence. The N55 ushers in forced induction without losing an ounce of smoothness or sanity. And the B58 responds by stretching limits even further beyond what the faithful could expect from a turbo inline-six.
For buyers still sitting on the fence between these iconic powerplants, rest easy. You simply can‘t make a poor choice reflecting the past and future of BMW six cylinder dominance. Let desire steer towards either abundant low-end punch or stratospheric redline enhancement. Both engines deliver in kind.