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Mercedes C 111 Was Futuristic Perfection

The enchanting prototype started off with rotary power and switched to diesel, breaking records with both engines.

Dan Carney

January 31, 2023

7 Slides

In 1969, the rotary engine was the future, and with its C 111 prototype, Mercedes-Benz aimed to showcase the potential of the compact, lightweight engine design.

At the time, every major automaker had licensed Felix Wankel’s rotary engine and aircraft engine maker Curtiss-Wright installed one of its prototypes into a 1965 Mustang hoping to interest Ford Motor Co. in the engine. General Motors designed its own engine, which would have been used in the Corvette and American Motors designed its unorthodox Pacer family car with the expectation of buying rotary engines for it from GM.

In this environment, Mercedes sought to demonstrate its technical prowess with a speedy sports prototype featuring a 280-horsepower three-rotor engine that could speed to 162 mph. The team progressed quickly, and Only five months later C 111-II was fitted with a four-rotor Wankel engine with an output of 350 hp. With this engine, the C 111 could reach 186 mph and scoot to 60 mph in just 4.8 seconds.

The engine wasn’t the only source of improvement. The C 111-II’s bodywork was improved in terms of vision for the driver as well as aerodynamic efficiency, with a coefficient of drag of 0.325, which was excellent for the time.

But other than Mazda, the world’s carmakers had little success producing durable rotary engines, as the three-sided rotors spinning inside them needed seals at their apexes that served in the role of piston rings in a reciprocating engine to seal combustion gases in the combustion chamber. Mazda was the only car company to succeed in developing apex seals, so the others gave up.

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They had little motivation to perfect the engine because, while it the design is powerful and compact, it is also thirsty and prone to making excessive pollution. The 1970s fuel shortages and price shock, along with increasingly stringent emissions restrictions led Mercedes, along with most of the industry, to abandon the rotary engine.

In addition to Mazda, Suzuki and Norton made rotary-powered motorcycles for a few years, but even in that application where compact size, light weight, and power are especially desirable, the rotary engine failed to catch on.

In response to demand for fuel efficiency, Mercedes pivoted to diesel power for its production models and revamped the C-111 with a production-based diesel engine to showcase the engine’s performance potential.

The engine was the five-cylinder three-liter naturally aspirated diesel from the 240 D 3.0 and 300 D, with a Garret turbocharger and an intercooler added, boosting the engine’s output of 80 hp to 190 hp to power the C 111-IID.

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The car set records at the Nardo test track in Italy on June 12, 1976. In total, 16 new records were set – those over 5,000 miles, 10,000 kilometers, and 10,000 miles. These were absolute world records, independent of the type of engine. The car averaged 158 mph.

In 1978, Mercedes was back, with narrowed and lengthened bodywork and the name C 111-III. This one carried a 230-hp version of the engine and had a Cd value of 0.183, the lowest rating ever achieved up to that time. The result this time was an average speed of more than 186 mph and 15 miles per gallon at that speed. By comparison, a rotary-powered car would have had similar fuel consumption in around-town driving.

Today we can still appreciate the C 111’s beauty and technical sophistication, so click through the photo gallery for more information.

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