During the next decade, the idea was kept alive, and a 90-degree vee angle version was experimented with. However, the engine was plagued by various technical issues, so the project was eventually canceled.
In the early 1980s, engineers got back to the drawing board, coming up with a design for an innovative V6 that could be scaled up to twelve cylinders. This time, it looked extremely promising, but once again, Mercedes higher-ups decided that its models would fare well with the existing M117 V8.
That changed in 1985 when they found out that archrivals BMW were preparing to introduce the second iteration of the 7 Series, a redesigned luxury sedan that was expected to be available with a new 296-hp, 5.0-liter V12. Concerned that sales of its popular W126 S-Class would take a big hit, Mercedes rallied the troops and accelerated the development of the new S-Class generation dubbed W140, which was in the works since 1981. At the same time, the powertrain department was given the green light to create a new V12 capable of outperforming the Bavarians’ upcoming M70 mill.
The scalable V6 that was tested several years earlier was abandoned, as the engineers opted for a different approach. They based the architecture of the new engine on the proven design of the M104 inline-six, which was basically the same recipe that BMW employed to cook up its twelve-cylinder.
Inside it, a forged-steel crankshaft with seven mains was fitted. The iron-plated, zinc-coated aluminum pistons connected to the crank via forged-steel conrods could reciprocate in liner-free cylinders thanks to the high silicon content of the block.
Both the diameter of each cylinder and the distance between each bore were the same as those of the M104 six, which enabled engineers to use its 24-valve aluminum cylinder head on the right bank of the M120. For the other bank, they cast a mirrored version of the component and integrated variable valve timing for the intake cams.
The engine also received a motorsport-derived, multi-piece oil pan to prevent foaming, a Bosch LH-Jetronic ECU coupled to knock sensors that allowed it to guzzle up lower-octane gasoline without risking pre-detonation, and a gorgeous one-piece intake manifold.
When it was finally ready, the 6.0-liter could develop up to 402 hp at 5,200 rpm, as week as healthy 428-lb-ft (580 Nm) of torque at 3,800 rpm. Even more impressive, roughly 90% of the torque was delivered to the rear wheels as early as 2,000 rpm, allowing the 4,000-pound (1,814 kg) S-Class to sprint from 0 to 60 mph (97 kph) in a little over six seconds.
BMW’s M70 was no match, and the only production V12s that could stand a chance against the M120 in terms of performance figures came from Ferrari and Lamborghini. It was so good that it was chosen by Horacio Pagani for his Zonda, one of the few novel supercars from the 1990s that managed to survive to this day.
Following the M120’s introduction, multiple tuning houses like AMG, Brabus, RENNtech, or Carlsson would enlarge the M120 and turn it into a monster, but the engine would achieve legendary status on track, courtesy of Mercedes’ long-time partners and future high-performance division, AMG.
The BPR was dominated by the McLaren F1, an iconic race car powered by a BMW V12 loosely derived from the 7 Series’ M70. Determined to enter the 1997 season and dethrone the McLaren-BMW partnership, the team of AMG and Mercedes engineers tasked with developing the new race car sourced a competition-spec F1 and fitted a thoroughly improved version of the M120 inside it. By doing this, they not only managed to reverse engineer the successful racecar but also test the new powerplant while the chassis and body were being developed.
Known internally as GT 112, the motor could spit out around 600 hp and proved to be extremely reliable. It helped the CLK GTR outperform BMW Motorsport’s McLaren F1s, as AMG-Mercedes secured both the Drivers’ and Teams’ trophies in their maiden season.
To compete in the FIA GT Championship, manufacturers were required to build a minimum of 25 road-going versions of the race cars. This gave birth to the CLK GTR AMG Strassen (street) Version, and with it, the AMG-tuned M120 hit the streets. Bored out to 6.9 liters, it made 604 hp at 6,800 rpm and 572 lb-ft (775 Nm) of torque at 5,250 rpm.
The first V12 mass-produced by Mercedes-Benz was not only the best twelve-cylinder in the history of the company but one of the best engines ever built. It started life as the heart of the epic W124 S-Class, then became a race engine in the successful CLK GTR, and finally aided the Zonda’s transformation from novelty to one of the most appreciated supercars of the 21st century.
You can learn more about this outstanding motor in the awesome video below posted on YouTube by Alfa Guy 2