The BMW straight-six engine: history of an icon
No engine is more BMW than the straight-six. From the "big six" of the 1960s to the turbocharged B58 and S58: the story of BMW's favourite engine layout and why it feels so special.
1 view 1 reading now 0 comments 6 min read
On this page
The BMW straight-six is more than an engine layout: it is part of the brand's identity. For decades, BMW has built six-cylinder engines with all cylinders in one line, known for their smoothness, their sound and their eagerness to rev, while many other manufacturers moved to V6 engines.
In this article we follow the history of the BMW straight-six, from the classic M30 and M20 to modern engines like the N54 and B58, and the legendary M engines such as the S54 and S58.
Why a straight-six is special
A straight-six, also called an inline six, has six cylinders in one row. This layout has a special advantage: it is naturally balanced. The forces created by the moving pistons cancel each other out, so the engine runs extremely smoothly without the need for balance shafts.
This smoothness gives the straight-six its typical character: a silky feel at low rpm, a clean pull through the rev range and a sound that many enthusiasts describe as the best of any engine type.
The disadvantage is length. A straight-six is longer than a V6, which makes it harder to fit, especially in cars with the engine mounted across the front. Many manufacturers therefore switched to V6 engines.
BMW, with its rear-wheel-drive cars and longitudinally mounted engines, had the space to stay loyal to the straight-six. It became one of the defining features of the brand.
The early years and the M30 "big six"
BMW built six-cylinder engines as early as the 1930s, for example in the BMW 303. But the modern story begins in 1968 with the M30, often called the "big six".
The M30 appeared in the large saloons and coupés of the time, such as the 2500, 2800 and the E9 coupés. It was robust, smooth and powerful, and it stayed in production for more than two decades. It powered many 5, 6 and 7 Series models, including the 535i and 635CSi.
The M30 earned a reputation for durability. Many of these engines covered enormous distances, and they are still loved by classic BMW owners today.
Its basic design also influenced BMW's motorsport engines, and it showed that a straight-six could combine refinement and performance.
The M20 and the "small six"
In 1977 BMW introduced the M20, a smaller straight-six for the 3 Series and the 5 Series. It made the six-cylinder engine available in compact cars, such as the 320i and 323i of the E21 and later the E30 3 Series.
The M20 used a timing belt instead of a chain and was known for its smoothness and its willingness to rev. It became very popular and helped to establish the image of the sporty, six-cylinder compact BMW.
Its timing belt needed regular replacement, which owners of classic BMWs still need to remember today.
Together, the M30 and M20 defined BMW's engine range of the 1970s and 1980s, and they built the reputation of the BMW straight-six as the smoothest engine in its class.
Four valves, VANOS and aluminium
In the 1990s BMW took the straight-six to a new level. The M50 of 1990 introduced four valves per cylinder to the regular six-cylinder range, and from 1992 it was one of the first engines with VANOS variable valve timing.
The M52 followed in the mid-1990s with an aluminium engine block in many markets, which reduced weight. Its updated version, the M52TU, received double VANOS. The M54 of 2000 continued this line and powered many 3, 5 and X5 models.
In 2004 the N52 introduced a block made of a magnesium-aluminium composite, which made it one of the lightest six-cylinder engines of its time, and Valvetronic, BMW's variable valve lift system.
These engines combined smoothness, power and lower consumption, and they made the BMW straight-six a reference in the premium car market.
The turbo era: N54, N55 and B58
In 2006 BMW introduced the N54, a 3.0-litre straight-six with two turbochargers and direct injection. It produced 306 hp in the 335i and impressed with its huge torque from low rpm. It also became famous among tuners for how much power it could handle.
The N55 of 2009 replaced it with a single twin-scroll turbocharger and Valvetronic, which made it more efficient and simpler.
In 2015 the B58 arrived as part of BMW's modular engine family. It is used in many current models, from the M340i to the X5 and the Toyota Supra. It is regarded as one of the best six-cylinder engines on the market: smooth, strong, efficient and robust.
Turbocharging changed the character of the straight-six, with much more torque at low rpm, but the smoothness and the sound remained.
The M straight-sixes
BMW M has built some of the most famous straight-six engines in history.
- M88 – the engine of the BMW M1 and the first M5, with four valves per cylinder.
- S38 – its successor in the E28 and E34 M5, with up to 340 hp.
- S50 and S52 – the engines of the E36 M3.
- S54 – the 343 hp engine of the E46 M3, revving to 8,000 rpm, often called one of the best naturally aspirated engines ever made.
- S55 – the twin-turbo engine of the F80 M3, F82 M4 and M2 Competition.
- S58 – the current twin-turbo engine of the M3, M4, M2 and X3 M, with up to more than 500 hp.
These engines show the full range of the straight-six: from high-revving naturally aspirated engines to powerful turbocharged ones.
The future of the BMW straight-six
As cars become electrified, the role of combustion engines is changing. BMW has introduced hybrid systems that combine six-cylinder engines with electric motors, and many new models offer fully electric versions.
But the straight-six remains an important part of BMW's range. It is used in many current models, including the M3, M4 and M2, and BMW continues to develop it to meet stricter emissions rules.
For enthusiasts, the straight-six is a symbol of what makes BMW special: smoothness, precision and a sound that is instantly recognisable.
Whatever the future brings, the BMW straight-six has already earned its place among the great engines in automotive history.
Key BMW straight-six engines
| Item | Details |
|---|---|
| M30 (from 1968) | The "big six", 2.5–3.5 litres |
| M20 (from 1977) | The "small six" for the 3 and 5 Series |
| M50 (from 1990) | Four valves per cylinder, VANOS from 1992 |
| N52 (from 2004) | Magnesium-aluminium block, Valvetronic |
| N54 (from 2006) | Twin-turbo, direct injection, 306 hp in the 335i |
| B58 (from 2015) | Modular turbo six in many current BMWs |
| S54 (2000–2006) | 343 hp, 8,000 rpm, E46 M3 |
| S58 (since 2019) | Twin-turbo M engine of the M3, M4, M2, X3 M |
Frequently asked questions
Why does BMW use straight-six engines?
A straight-six is naturally balanced, which makes it very smooth, and it has a distinctive sound. BMW's rear-wheel-drive cars with longitudinal engines have the space for its length.
What is the best BMW straight-six engine?
Many enthusiasts name the S54 of the E46 M3 for its high-revving character, and the B58 for its mix of power, efficiency and reliability. The answer depends on what you value.
Which BMW straight-six is turbocharged?
The N54, N55 and B58, as well as the M engines S55 and S58, are turbocharged straight-sixes.
Is the BMW B58 a good engine?
The B58 is widely regarded as one of the best modern six-cylinder engines: smooth, powerful, efficient and robust. It is used in many BMWs and in the Toyota Supra.
Comments 0
Join the conversation — be kind, no links.
Loading comments…