The Wankel Mercedes-Benz

In the spring there was a great rustling in Europe, and in other parts of the world, when the mighty Daimler-Benz empire let it be known that they had developed a three-rotor Wankel engine for use in a Mercedes-Benz sports coupé. Had any lesser firm made such an announcement it would have been met with mild curiosity, but when Daimler-Benz do something everyone takes it seriously, for they are serious people. As if the advent of a Daimler-Benz Wankel-motor was not enough, there was the added interest that it was installed in a sports coupé of classic lines and the car was mid-engined. Now a mid-engined coupé is nothing to get excited about, for this is the layout that is universal in sports-car racing today, and firms like Matra, Lotus, Ferrari, Porsche and Lamborghini are in production with such cars; for Daimler-Benz to show signs of manufacturing such a car is another matter, rather as it Jaguar had announced a V12-cylinder car with a Lamborghini Miura layout. Powerful engineering empires are really very conservative in what they let out to the public gaze, even though they may be very advanced in their experimental departments, so we can rest assured that the mid-engined Wankel Mercedes-Benz is not just a flight of fancy or a publicity stunt, it is a serious project. Since the gull-wing 300SL there has not been a true sports car from Daimler-Benz, although they have always offered open roadsters, like the present 280SL, so many people have felt for some time that a successor to the 300SL has been long overdue. Mind you, when a firm markets a vast limousine, more advanced technically than any other car, which does well over 120 m.p.h., with handling to match, and a compact five-seater saloon good for well over 130 m.p.h., there seems little point in making a sports car. Any sports car they do produce would have to be exceptional, in the GT40 Ford or Lola-Chevrolet category of performance and handling, and this is what it looks as if they have done with their new model, the C111.

The Wankel engine has been in existence for many years, N.S.U. and Curtiss-Wright being the first to start serious development on it as a replacement for the normal piston engine. N.S.U. went straight to the heart of the matter and built a single rotor unit of very small proportions which they put in the rear of a Sport-Prinz open two-seater, while Curtiss-Wright concentrated on large diameter stationary engines for industrial purposes. Basically the engine of Felix Wankel, a German engineer, is a triangular rotor revolving in a specially shaped barrel, the corners or edges of the triangle rubbing against the casing at various points thus forming ever-changing wedge-shaped spaces, which are the combustion spaces for a normal four-stroke Otto cycle, inlet and exhaust ports being covered and uncovered by the rotor as it goes round. When the compressed fuel/air mixture is fired the power released pushes the rotor on round in its path, the other lobes continuing the process of the Otto cycle. After some early troubles with lubrication and gas sealing, N.S.U. had their engine so perfected that they went into full-scale production with a twin-rotor version in the -current Ro80 saloon. The little single-rotor Prinz two-seater did a lot to overcome initial cautiousness on the part of the public, and few people who drove the Prinz found any complaints about the Wankel engine.

Meanwhile, N.S.U. and Wankel had offered the engine patents for sale under licence and Mazda in Japan and Daimler-Benz in Germany took up the offer. The Japanese were very quick on development, having no engineering traditions to risk if anything went wrong, and the twin-Rotor Mazda 110 coupé was soon on the market, and Motor Sport was very enthusiastic about it when they road tested it. At the Spa 24-hour race in July two Mazda Wankel-engined saloons finished fifth and sixth, creating a tremendous impression by their speed and reliability, to say nothing of the noise from the open exhausts. Now with Daimler-Benz releasing full details of their Wankel-engined car and exhibiting one at the Frankfurt Motor Show this month, it must be accepted that the Wankel engine has really arrived, as also has the mid-engined two seater sports car.

The first car that Daimler-Benz built was essentially a test chassis for the engine, but it is interesting that it was modelled very much on present-day sports/prototype racing practice, using wide-tread racing Dunlop tyres. A rough and sketchy coupé body was built on to the platform chassis frame and the car was known as the C101 prototype, various photographs of it on test as Hockenheim being released. The second car was much nearer a road-going version, but still a long way off a pre-production prototype, and it is this car that is featured in the accompanying photographs. By the Frankfurt Motor Show a third one will be in existence. At the moment the car is an experimental probe to test public reaction and will no doubt go into limited production as did the gull-wing 300SL in its day, while more than likely it will form a test vehicle for the Wankel engine before it appears in production saloons, in the way N.S.U. did with the Sport-Prinz. As Porsche found out some years ago, model designation with a zero in the middle of a number, as far as serious production is concerned, is patented by Peugeot, so the Wankel Mercedes-Benz is now known as the C111 or C-one-eleven.

The engine of the C-one-eleven has three rotors and each one displaces 600 c.c. per lobe, giving 1,800 c.c. combustion space total for the three rotors. The agreed F.I.A. Formula for Wankel engines, says two-thirds of the volume swept by each rotor in one revolution is taken as the equivalence with a normal piston engine, so that each Mercedes-Benz rotor sweeps 3 x 600 c.c. = 1,800 c.c. and two-thirds of that is 1,200 c.c., so that the three rotors count 3,600 c.c. or 3.6 litres. Power output is quoted as 280 horsepower DIN at 7,000 r.p.m. with maximum torque between 5,000 and 6,500 r.p.m.; the DIN horsepower figure being with all accessories and exhaust system, as set up for use on the road. A three-stroke mechanical fuel-injection pump feeds the rotors and there is one sparking plug to each rotor fired by a transistor system. The unit is water cooled, a radiator being carried in the nose of the car. At present the engine is coupled to a normal ZF 5-speed gearbox/axle unit, as used by Ford in the GT40 and the whole assembly is mounted in a fabricated steel chassis, also on the lines of a GT40, with fuel tanks in the door sills, and this construction is extended in a hoop over the rear of the cockpit to form the roof line and act as a crash bar. Body panels are in glass-fibre, the front looking like a GT40 and the rear like a Lotus Europa, while gull-wing doors so successful on the old 300SL, are used. As must be accepted with a mid-engined coupé, unless it is a Rover BS6, the C111 is a pure two-seater with separate hammock type seats and at the moment luggage room is under the tail and rudimentary. Headlamps are in pairs under hinged lids, lifted by vacuum and lowered by a foot-operated spring release, and there are spot lamps located under the nose. The wheelbase is 8 ft. 7½ in., the height a nominal 44 in., and maximum speed is quoted as 260 k.p.h. (161 m.p.h.) with 0-60 m.p.h. in under 5 sec.

Taken as a complete car the C-one-eleven does not seem such an enormous step forward as the 300SL did in 1952 or the 300SLR in 1955, but looked on as a test-bed for the Daimler-Benz 3-rotor Wankel engine it comes into perspective as the beginning of a new era in which NSU and Mazda have already done a great deal of spadework.—D. S. J.