For the latest edition of our Deep Dive Engine Series, we take a closer look at Mercedes-Benz’ M120 Engine, the iconic V12 found in flagship variants of the W140 S Class, R129 SL, and perhaps most famously, the Pagani Zonda.

Let’s go back to 1991

When Bruno Sacco’s W140 S-Class first debuted in 1991, it was the epitome of luxury, technology, and performance. At the top of the model hierarchy was the ground-breaking all-new 6.0L V12 powered 600 SE and SEL.

That powerplant, the M120 V12 engine, shall be today’s focus:

Mercedes-Benz M120 V12 Engine. Spotlight-Leicht

Introducing The M120 Engine

Mercedes’ first ever production V12 engine was introduced in competition to staunch rivals BMW, who had launched their relatively primitive M70 V12 engine in the late 80s.

BMW M70 V12 Engine. Hagerty

Ok ok, BMW may have got their ducks in a row with the closely related S70/2 (which had similar bells and whistles to the M120 – advanced heads for example, boasting dual overhead cams, 4 valves per cylinder and VANOS variable valve timing) – which found its way into the er, cough, McLaren F1. No big deal.

The infamous McLaren F1. McLaren Automotive

Yes, it’s probably the greatest road car of all time, but you’ll never get to experience one of those (unless you have $20 million or so lying around to blow on a car) so it’s not worth much of a mention.

The M120 engine was officially released in 1991 with the new W140 S-Class after a delay to allow for further development.

Mercedes-Benz W140 S-Class. Forced Induction

With its mammoth 6.0 litre displacement, it produced 402 hp at 5,200 rpm and 428 lb-ft (580 Nm) of torque at 3,800 rpm. It delivered 90% of its torque at 2,000 rpm, enabling a 0-60 mph dash in just over six seconds, with some magazines recording even quicker times than that.

Mercedes-Benz W140 S Class – ’The Future in Motion’ – 1991

That’s a serious sprint in the completely over engineered, technology-stuffed and therefore pretty porky W140. BMW’s M70 V12 with its measly 295 hp was significantly outperformed by the M120, with only the Italians offering competitive V12 engines at the time via Lamborghini and Ferrari.

1991 Ferrari 512 TR. Ferrari

Background and Development

The roadmap to the M120 was long and arduous. Mercedes-Benz’s quest to develop a twelve-cylinder engine in the post-war era began in the 1960s. During this period, they designed a 7.5-liter V12 prototype intended for the luxurious 600 Pullman limousine.

1973 Mercedes-Benz 600 Pullman. Duncan Hamilton ROFGO

However, despite the promising potential of this engine, it was ultimately shelved in favour of the existing V8 line-up, which was considered sufficient. The ambition to build a V12 engine persisted into the 1970s. Engineers experimented with a 90-degree design, but the project was plagued by technical difficulties which led to its eventual abandonment. The concept of a V12, though compelling, remained elusive.

In the early 1980s, Mercedes engineers revisited the V12 concept by designing a scalable V6 that could be expanded to twelve cylinders, but priorities from management shifted to the M117 V8.

Mercedes-Benz M117 V8 Engine. Sportlich-Leicht

The project was revived in 1985 due to competition from BMW, who were developing the M70 V12 engine for their planned 7 and 8 series flagships. Mercedes aimed to outdo this with a new V12 for the W140 S-Class, which had been in near unlimited-funds development since 1981.

 The New S-Class. Mercedes-Benz

The V6 basis was dropped, with the engineers opting for a different approach – to essentially mate two M104 straight 6 engines together. It was a similar approach to BMW and the design of their M70 engine. But better. Mercedes’ engineering is akin to art, and as the saying goes, good artists copy, great artists steal…

Engineering Excellence

The M120 engine’s design was influenced by the architecture of the M104 straight six, offering a unique blend of innovation and proven engineering.

An AMG-tuned M104 straight 6 engine. Mercedes-AMG

Initially, the engine featured a cast-iron block, but engineers transitioned to an advanced aluminium-alloy construction containing 17% silicon and 4% copper. This change resulted in significant weight savings, improved power output, and enhanced reliability. The M120’s core consisted of a forged-steel crankshaft, iron-plated, zinc-coated aluminium pistons, and liner-free cylinders, all working in unison to deliver exceptional performance. The engine shared cylinder dimensions with the M104, allowing for the adaptation of similar 24-valve aluminium cylinder heads, complete with dual overhead camshafts and variable valve timing on the intake cams. Bosch’s LH-Jetronic engine management system was deployed for superior efficiency, utilising dual throttle bodies, mass airflow sensors and engine control units.

Purchase parts for your M120 equipped Mercedes-Benz here:

Buy an M120 MAF Sensor

Buy an M120 Throttle Body – Right Side

Buy an M120 Throttle Body – Left Side

Buy an M120 LH Engine Control Unit

The Evolution of the M120

The M120 engine went through several updates during its production run to enhance its performance, reliability, and emissions characteristics. The early versions of the M120 (120.980), used in the W140 S-Class and C140 SEC, were renowned for their effortless power and refinement. These cars were the ultimate expression of Mercedes-Benz luxury and engineering prowess.

Mercedes-Benz C140 600 SEC. Car and Driver

In 1993, an updated M120 (120.981), found its way into the R129 SL-Class via the 600 SL. For the first time in its prestigious history an SL was equipped with a V12 engine. This made the R129 SL one of very few roadsters of the era available with a twelve cylinder powerplant, combining open-top motoring with unrivalled power, refinement and luxury.

Mercedes-Benz R129 600 SL. PCarMarket

The final iterations of the M120 (120.982 and 120.983) introduced refinements to the admittedly complicated vacuum system, as well as the engine management system with the introduction of Bosch Motronic, an integrated distributor-less ignition and injection system, as with other engines in the Mercedes-Benz line-up, further improving performance, efficiency and diagnostic capability. By this time, the M120 had firmly established itself as one of the finest V12 engines ever produced.

Applications Beyond Stuttgart

The M120’s capabilities extended beyond the realms of Mercedes-Benz. The base 6.0 litre engine was selected as the powerplant for the Pagani Zonda C12, a supercar that would go on to become a legendary piece of automotive art in its own right.

The M120 powered 1999 Pagani Zonda C12. Motor1.com

Later versions of the Zonda used an AMG modified M120, first a 7.0 litre, then a 7.3. This sparked the beginning of a now decades-long partnership between the two outfits, with Pagani’s lauded creations loyally powered by Mercedes-AMG engines to this day.

The 2024 Pagani Utopia, powered by a Mercedes-AMG engineered M158 engine. Motor Authority

The M120’s versatility attracted the attention of many renowned tuning houses such as the aforementioned AMG, as well as Brabus, RENNtech, and Carlsson, who pushed the M120 to even greater heights, unleashing its full potential through various modifications. It would be sacrilege not to mention possibly the most famous R129 of them all, the AMG-tuned ultra low volume SL 73 – featuring a near identical version of the 7.3 litre M120 used to power the Pagani Zonda S 7.3. An S 73 was also produced for the 140 chassis utilising the same engine.

Mercedes-Benz R129 SL 73 AMG. autoevolution

The AMG-tuned 7.3 Litre M120 variant found in the R129 SL 73, and S 73. Carscoops

Use in Racing

Following the collapse of the DTM championship in 1996, Mercedes-Benz sought new racing opportunities and turned its focus to the BPR Global GT Series. The racing scene was dominated by the McLaren F1, powered by the previously mentioned S70/2 BMW V12. Determined to compete at the highest level, Mercedes, in collaboration with AMG, developed the CLK GTR. The vehicle featured an upgraded version of the M120 engine, internally known as GT 112, producing around 600 horsepower. This engine played a pivotal role in Mercedes’ success, as the CLK GTR outperformed its rivals, securing both the Drivers’ and Teams’ titles in the FIA GT Championship of 1997.

Mercedes-Benz CLK DTM GTR. Hagerty

As per the DTM homologation rules of the time, Mercedes-Benz were obligated to produce a road-legal ”homologation special” of the CLK GTR in limited numbers. Named the Strassenversion, the road-legal GTR was a similar project to the Porsche 911 GT1, with the two often compared and contrasted in motoring media.

Porsche 911 GT1. DriveMag Cars

Only one road car was completed in 1997 for the Frankfurt Motor Show, with the rest produced by AMG and HWA from 1998 to mid-1999. The road cars shared many components with the race car, including the suspension, transmission, and carbon-fibre monocoque. Out of 28 cars produced, 2 were prototypes, 6 were roadsters, and 20 were coupés, including 2 ”SuperSport” models. Additionally, a coupe and a roadster were produced in right-hand drive configuration for, you guessed it, the Sultan of Brunei.

Mercedes-Benz CLK GTR Strassenversion. Top Gear

Legacy and Enthusiast Appeal

The M120 engine remains a favourite among Mercedes enthusiasts, collectors and hot rodders. Its combination of engineering excellence, performance, refinement and smoothness has stood the test of time. Well-maintained examples are highly sought after, and the engine’s reputation for reliability makes it a prized possession.

A Collector’s Dream

The M120 engine is more than just a powerplant; it is a symbol of Mercedes-Benz’s dedication to creating the ultimate motoring experience. Whether nestled in the engine bay of an S-Class, CL, SL or Pagani, the M120 represents the zenith of automotive engineering. If you’re lucky enough to own an M120-powered vehicle, you have one of the finest engines ever produced by Mercedes-Benz. You own a piece of automotive history. These vehicles are a testament to Mercedes-Benz’s commitment to producing the very best… or nothing. Enjoy it, and contact us anytime you need parts or advice.

Buy a Mercedes-Benz M120 Engine here