In the 1990s, performance was measured by engine displacement and the number of cylinders, and both BMW and Mercedes-Benz were eager to push the limits of automotive engineering. At the time, BMW embarked on its V16 project for its flagship 7 Series, but Mercedes-Benz made an even bolder move. The automaker developed an 18-cylinder “W” engine, a technological marvel intended to power the W140 S-Class, specifically a model named the 800 SEL.
Despite its extraordinary power and performance, this W18 engine, codenamed M126, was never mass-produced. Although technically feasible, the ambitious project was ultimately doomed by practical challenges such as size, fuel efficiency, and cost. The W18 remains one of Mercedes-Benz’s most ambitious yet unrealized projects.
A Masterpiece of Engineering: The W18 Engine
The W18 was an extraordinary piece of engineering. It consisted of three 2.6-liter inline six-cylinder engines, each derived from the M103 engine family, arranged at a 75-degree angle to form the “W” layout. Two engine versions were developed: a 36-valve version with two valves per cylinder and a more advanced 90-valve version with five valves per cylinder. The engine could produce up to 680 horsepower, a staggering output for the time that placed it on par with the likes of Bugatti and Ferrari.
This power was more than enough to surpass the performance of the existing 600 SEL, which featured a 6.0-liter V12 engine. Mercedes-Benz aimed to incorporate the W18 into the flagship 800 SEL sedan, taking the luxury sedan segment to new heights. However, several technical hurdles soon became apparent.
Technical and Practical Challenges
Despite its impressive specifications, the W18 engine presented significant challenges in terms of packaging and integration. The engine’s sheer size made it too wide and heavy for the S-Class platform, complicating installation and requiring redesigns of numerous other components, such as the suspension, cooling system, and exhaust layout.
Fuel efficiency was another major issue. The W18 engine’s 18 cylinders demanded a substantial amount of fuel, making it far too inefficient for a luxury car designed for high-end consumers. The development and production costs for such a complex engine were prohibitively high, making mass production unsustainable.
Economic Realities and the End of the 800 SEL
Ultimately, the 800 SEL project was scrapped due to economic realities. Mercedes-Benz recognized that despite the engine’s impressive performance, the cost of producing a car with this powertrain would not yield a viable return on investment. The 600 SEL, equipped with the 6.0-liter V12 engine, was already providing more than enough performance for the luxury sedan market, and the new M120 V12 engine proved sufficient for Mercedes-Benz’s flagship.
As a result, the 800 SEL never made it past the development stage. Mercedes-Benz’s decision was pragmatic, focusing on producing vehicles that met both performance demands and market feasibility.
A Shared Dream: BMW’s V16 and the End of an Era
Interestingly, Mercedes-Benz was not alone in its bold, high-cylinder ambitions. BMW also developed a V16 engine for its 7 Series—referred to as the “Goldfish” project—but ultimately abandoned it for similar reasons. Both automakers had proven the technical feasibility of these monumental engines but faced the harsh realities of cost, practicality, and market demand.
While these projects may seem extravagant by today’s standards—especially as the automotive industry shifts toward electrification—they represent the last era of automakers dreaming big with traditional internal combustion engines. These once-ambitious powertrains may have never seen mass production, but they remain an important part of automotive history, representing a time when performance was king and engineering limits were constantly being pushed.
