The BMW S38 Engine: A Technical Dive into an Icon

The BMW S38 Engine: A Technical Dive into an Icon

The BMW S38, a name that resonates with automotive enthusiasts and engineers alike. For many, it evokes images of the iconic BMW M5 tearing down the Autobahn, its straight-6 heart purring and roaring in harmonious symphony. But beyond the romanticized imagery, the S38 stands as a testament to BMW's relentless pursuit of engineering perfection and a desire to push the boundaries of performance.

Born in the mid-'80s, the S38 was conceptualized as a replacement for the legendary M88. Initially introduced for North America, it boasted a slightly subdued power output, tailored to meet the region's specific demands. But like a fine wine, the S38 only got better with age. By 1989, not only did it see a power hike, but it also proudly took over the mantle as the worldwide successor to the M88.

In this deep dive, we will journey through the intricate details of the S38, understanding its design intricacies, its evolution over the years, and the legacy it left behind. So, fasten your seatbelts, as we embark on this technical voyage into one of BMW's most iconic engines.

The Genesis of the S38

The roots of the S38 can be traced back to its illustrious predecessor, the M88. The M88, with its raw power and performance, had already set a high benchmark in the automotive world. It was the engine that powered the famed BMW M1 supercar, an engine that left an indelible mark on automotive enthusiasts worldwide. Yet, as times changed and the world moved towards stricter emission norms and standards, BMW realized the need for an evolution.

Enter the S38. Initially conceived for the North American market, this engine was more than just a successor. It was a response to a changing automotive landscape. North America, with its distinct emission regulations and consumer preferences, required an engine that could balance power with compliance. The S38 delivered on that promise, albeit with a slightly tempered power output compared to the European M88.

However, the journey of the S38 was just beginning. By the end of the '80s, BMW made a pivotal decision. The S38 was not just going to be a regional powerhouse; it was destined for a global stage. In 1989, with increased power output and a series of refinements, the S38 stepped up to become the worldwide standard-bearer, replacing the M88 across all markets.

This transition was not just about numbers and specs. It was a statement. A statement that BMW was ready to adapt, innovate, and continue its legacy of producing some of the world's most revered engines. The S38 was not just a successor; it was the dawn of a new era.

Design and Anatomy

Delving beneath the hood and into the heart of the S38 reveals an engine designed with both performance and refinement in mind. Its lineage, unmistakably rooted in the M88/3 engine, gave it a strong foundation to build upon. Yet, the S38 wasn't just a rehashed version of its predecessor; it was a reimagined masterpiece.

Compression Ratio: Starting with the compression, the S38 sported a ratio of 9.8:1. While this was slightly lower than the M88/3, it was a strategic decision, allowing the engine to perform optimally with a variety of fuel qualities across different regions, particularly in North America.

Exhaust System: The S38 showcased a simplified exhaust manifold. In tandem with the introduction of a catalytic converter, this not only improved emissions but also ensured the engine met the rigorous standards of the time.

Timing Chain: The dual-row timing chain was another pivotal design element. Offering enhanced durability and precision, it ensured that the S38's complex valvetrain operated with clockwork accuracy.

Camshaft Duration: A shorter camshaft duration was chosen for the S38. This tweak was pivotal in achieving a more linear torque curve, providing drivers with responsive power delivery across a wide RPM range.

Valvetrain: A technical marvel in its own right, the S38's DOHC valvetrain utilized shim-and-bucket valve actuation. This design, while intricate, ensured robust performance and reduced maintenance requirements over the engine's lifespan.

Air Intake System: Perhaps one of the most distinct features of the S38 was its air intake system. Six individual throttle bodies, each crowned with its own intake trumpet, fed air into the engine. This setup, combined with a cast aluminum intake plenum, ensured that the engine breathed freely, optimizing power delivery and throttle response.

The sum of these parts was an engine that, while drawing inspiration from its predecessor, carved its own identity. The S38 was more than just metal, oil, and combustion. It was a symphony of engineering, each component harmonizing to create a driving experience that was quintessentially BMW.

Evolution of the S38: A Look at the Different Versions

Over its illustrious lifespan, the S38 underwent several refinements, giving birth to different versions, each with its own unique characteristics. Let's navigate through these evolutions, understanding the nuances that set each version apart.



The S38B35 was the initial iteration, characterized by a bore of 93.4 mm and a stroke of 84 mm. While it was designed with North America in mind, its applications soon expanded.

    • Displacement: 3,453 cc
    • Power: 190 kW (255 hp) @ 6,500 rpm
    • Torque: 330 N⋅m (243 lb⋅ft) @ 4,500 rpm


    • 1986-1987 E28 M5 (Canada, Japan, and USA)
    • 1986-1988 E24 M6 (Canada, Japan, and USA)
    • 1987-1989 E24 M635CSi (models equipped with a catalytic converter)



With the S38B36, BMW took the engine to new heights. The displacement saw a bump, primarily achieved by increasing the stroke to 86 mm using a new forged steel crankshaft. Additionally, the engine benefited from a series of upgrades, including revised camshafts and an increased compression ratio of 10:1. Innovations like a variable-length inlet manifold for improved low-rev torque, stainless steel exhaust headers, and a hotwire MAF, coupled with Bosch Motronic engine management, further refined its performance.

    • Displacement: 3,535 cc
    • Power: 232 kW (311 hp) @ 6,900 rpm
    • Torque: 360 N⋅m (266 lb⋅ft) @ 4,750 rpm


    • 1988–1992 E34 M5 (worldwide)
    • 1989–1993 E34 M5 (Canada and US)



The pinnacle of the S38's evolution was the B38 variant. BMW expanded the engine further to 3,795 cc by stretching both the bore to 94.6 mm and the stroke to 90 mm. But the changes weren't just about size. The engine management shifted to the advanced Motronic 3.3, and the ignition system embraced coil-on-plug technology. Other enhancements included a hike in compression ratio to 10.5:1, the introduction of a dual-mass flywheel, larger intake and exhaust valves, lighter pistons, and throttle bodies that grew to a diameter of 50 mm.

    • Displacement: 3,795 cc
    • Power: 250 kW (335 hp) @ 6,900 rpm
    • Torque: 400 N⋅m (295 lb⋅ft) @ 4,750 rpm


    • 1991-1995 E34 M5 (European-specification)

As we journeyed through these versions, it became evident that BMW wasn't content resting on its laurels. The S38, throughout its tenure, was a canvas of innovation and relentless pursuit of perfection. Each iteration was not just an upgrade but a testament to BMW's commitment to pushing the envelope in automotive engineering.

The Legacy and Transition

As the sun began to set on the S38's production run, BMW was already looking towards the horizon, preparing for the next chapter in its high-performance engine saga. The S38 had served well, powering some of BMW's most iconic vehicles, earning accolades, and cementing its place in automotive lore. Yet, the world of motoring is one of constant evolution, and by the late '90s, BMW felt the winds of change.

In 1998, the BMW M5, which had been the S38's most illustrious home, transitioned to a new heart: the S62 V8 engine. With eight cylinders, the S62 represented a departure from the straight-six configuration that had been a hallmark of BMW's M division for so long. This new engine offered more power, a broader torque curve, and innovations that positioned the M5 as a modern performance benchmark.

However, for purists and enthusiasts, the transition was bittersweet. The S38, with its unique character and straight-six song, had a charm that was unmatched. Its legacy wasn't just about horsepower or torque figures; it was about soul, character, and a distinct personality that endeared it to many.

But the S38's spirit didn't fade into obscurity. Elements of its DNA were carried forward in the BMW S50 engine, which took over as BMW's high-performance straight-six engine. While not a direct successor, the S50 was a torchbearer, continuing the tradition of BMW's commitment to engineering excellence.

In conclusion, while engines come and go, legends like the S38 leave an indelible mark. Its symphony, a blend of mechanical artistry and raw power, continues to echo in the hearts of automotive enthusiasts worldwide. The S38 may have given way to newer engines, but its legacy is immortal, a testament to a time when BMW crafted not just engines, but experiences.


The story of the BMW S38 is more than just the tale of an engine. It's a narrative of innovation, of passion, and of an undying commitment to driving excellence. From its inception as a North American counterpart to the M88 to its evolution as a global powerhouse, the S38 embodied the spirit of BMW's M division.

In a world dominated by figures, specs, and 0-60 times, the S38 reminded us of the soulful side of motoring. The growl of its straight-six, the responsiveness of its throttle, and the sheer exhilaration of pushing it to its limits are experiences that numbers can't capture.

As we reflect on its journey, the S38 stands as a testament to BMW's engineering prowess. It wasn't just designed to meet standards or fill a slot in a lineup; it was crafted with a purpose. A purpose to deliver unparalleled driving joy, to connect the driver with the road, and to create memories that last a lifetime.

While the automotive world moves forward, with electric drivetrains, autonomous systems, and AI integration, the legend of the S38 serves as a reminder of a golden era. An era where the bond between man and machine was sacred, where every drive was an adventure, and where engines like the S38 were the beating hearts of automotive masterpieces.

In the annals of automotive history, the BMW S38 will forever be remembered not just as an engine, but as an icon. An icon that celebrated the art of driving in its purest form.