A tale of Wankel engines, turbocharged diesels, stunning looks and world records
The C111 test cars that hurtled round the test tracks of Europe in the late sixties and early seventies may have made it look like Mercedes were indulging in some futuristic fantasies of no relavance to the period. In fact they were successfully testing many of the ideas that have since made it into mainstream production. That, and having a lot of fun of course.
The first cars were used to test out Mercedes' plans for rotary engines. The company had declared that it would put a rotary engine into production cars. It set its men in white coats the task of developing and proving such an engine. The three-rotor Wankel engine in the first C 111 of 1969 developed 280 hp, giving the car a top speed of 160mph.
Using the C 111 prototypes they experimented with the motors and also a number of other innovations. Some of those we benefit from today including suspension configurations allowing wide tyres and plastic bodywork to reduce weight and improve aerodynamic efficiency.
The next iteration - the C 111-II - was fitted with a four-rotor Wankel engine with an output of 350 hp. It gave the car a top speed of 180mph and could accelerate to 60mph in 4.8 seconds. Compared to the C111-I, this version had bodywork that had been improved significantly in terms of vision for the driver as well as aerodynamic efficiency. The Cd was 0.325, not bad at the time. The most important aspects, however, were the clearly improved flexibility of the Wankel engine and its torque raised to 290ft-lb, superior to most contemporary road-going cars.
The company introduced the second generation car to the public at the Geneva Motor Show in March 1970. It went down a storm with the punters who longed for a dramatic and beautiful successor to the 300 SL Gullwing coupe.
Production hopes were dashed though by ever more stringent emission legislation in a large number of countries and finally by the 1973 oil crisis. The pollutant emissions of Wankel engines were difficult to reduce and they also had a relatively high fuel consumption, neither of which was endearing to those campaigning for more environmentally friendly engines.
Wondering where to go next with the project, Mercedes struck upon idea of using diesel engines to set speed records and the engineers were sent back to their labs to sort it out. The engine suggested was the five-cylinder three-litre naturally aspirated diesel from the 240 D 3.0 and 300 D, an engine with plenty of potential for raising performance.
With a Garret turbocharger and an intercooler, the production engine’s output of 80 hp was boosted to a proud 190 hp to power the C 111-II. It was rolled out for a record attempt at the brand-new test track in Nardo on June 12, 1976. Four drivers, who took turns at two-and-a-half hour intervals, drove this car from one diesel record to the next over a time-span of 60 hours. In the end, a total of 16 new records had been established - those over 5,000 miles, 10,000 kilometers and 10,000 miles even were absolute world records, i.e. independent of the type of engine. Speed averaged around 150mph. The diesel had proved its ability to race.
The achievements of the second generation model had got Mercedes quite excited by now and they pressed on with the third generation car. It would be a thoroughbred racing car with aerodynamic features refined down to the smallest detail and giving the car a Cd value of 0.183, the lowest rating ever achieved up to that point in time. The car had a longer wheelbase than the C 111-II, a narrower track, concealed wheels, a very low front end with recessed, powerful headlamps and a very long and tapering rear end with a central fin that was to enhance the car’s straightline stability under side wind conditions.
They continued down the diesel route with a turbocharged five cylinder diesel unit. The turbo span at 130,000rpm, pressing enough air into the combustion chambers to boost the output to 230 hp. They were aiming for 200mph!
Finally, on April 30, 1978, the time had come for the diesel-engined record car to drive lap after lap at constant speed on the Nardo track - anti-clockwise because this meant that the crash barriers were on the right-hand side, providing the drivers of the LHD cars with a greater safety margin in the event of an accident.
At one stage during the night, radio communication saved a hedgehog’s life: it was rescued in time before crossing the racing car’s lane. More drama ensued when the rear tyre on the right-hand side burst during the third driver’s stint at night-time, tearing large holes into the bodywork. The recovery truck arrived on the scene quickly to pick up the damaged car and its uninjured driver, while the mechanics prepared the identical reserve car. After this incident, clocks were reset to zero and the hunt for records began anew.
The reserve car was even a whisker faster than the original car, and also a little more economical, extending the refueling intervals from 62 to 67 laps. The three drivers were soon joined and relieved by their extremely fast project manager, Dr. Hans Liebold.
All records established by the first car were bettered by the reserve car - despite another hedgehog splattering itself on the front spoiler!
After 12 hours of otherwise problem-free driving, Mercedes-Benz had nailed nine new absolute world records its own, i.e. records irrespective of the type of engine and its displacement.
World Circuit Record
It wasn't enough though. A world circuit record of 355.854 km/h had been in existence since 1975, established by a 1,000 hp racing car from the American Can-Am series. Though not recognized by FIA, it was a highly desirable world record, and after the successes with the C 111-III, the Mercedes-Benz engineers felt that it was within reach. Just another 100 hp would do - but could no longer be squeezed out of the near-production diesel.
The team opted for the 4.5 litre V8 petrol engine from large-scale production, raised its displacement to 4.8 litres and equipped the unit with sodium-cooled valves, two KKK turbochargers and a triple-plate clutch that was capable of coping with 600 Nm torque.
C 111 - IV
With 500bhp on tap, achieved at relatively low expense, a C 111-IV modified into a racing car with further aerodynamic improvements - two fins and additional spoilers - set out in Nardo on May 5, 1979 to have a go at the world circuit record. After a smooth run, a new record of 403.978 km/h (250mph) had been established.
It was a suitable end to a generation of innovation and experimentation. Another chapter from Mercedes history that could be duplicated in the record books.