- 300 SL (W 194): With serial components developed for racing
- 300 SL (W 198) and 190 SL (W 121) followed as production sports cars
The Mercedes-Benz 300 SL (W 194 series) racing sports car came as an overwhelming surprise: although people had hoped for a car like this from Mercedes-Benz during the post-war period, it still left the world speechless when it was presented in March 1952. That same year, the 300 SL enjoyed enormous success at all the major international racing sports car events. Despite its surprise effect, however, the 300 SL racing sports car was not a product of chance, but the result of thorough engineering work. From it emerged the W 198 series production sports car with the identical model designation, 300 SL. The Mercedes-Benz 190 SL (W 121) was developed in parallel. The brand showed both cars in February 1954 at the International Motor Sports Show in New York and received a tremendously positive response.
Development of the 300 SL racing sports car (W 194)
In 1951, the then chairman of Daimler-Benz AG, Wilhelm Haspel, had his experts keep a watchful eye on the international motor sport scene. To Haspel, involvement in motor sports was key to restoring added lustre to the company’s global reputation once again. He was confirmed in this view by the many enquiries he received from 1946 onwards, especially from English-speaking countries, asking when Daimler-Benz intended to return to international racing.
On the other hand, involvement in grand prix racing was rendered relatively uninteresting by the decision of the FIA (Féderation Internationale de l’Automobile) to introduce a new racing car formula from 1954 (2.5-litre displacement for naturally aspirated engines or 0.75-litre displacement for supercharged engines). The term remaining for the 1.5-litre formula still in force hardly justified the development of a completely new racing car under that formula – although the company did look into the possibility in a project designated W 195. This did not get beyond the planning stage, however. And although still in existence, the pre-war W 165 was no longer competitive. So to comply with Haspel’s demands, the only course of action was to engage in sports car racing.
Haspel saw a clear opportunity here and his basis were the new 220 and 300 passenger car models with their new OHC engines introduced in the spring of 1951 at the International Motor Show (IAA) in Frankfurt am Main. For it had not gone unnoticed in Untertürkheim that Jaguar had achieved success in international racing with the XK 120 sports car developed using components of its 3.5-litre Mark VII saloon.
It had been decided that the representational 300 Saloon (W 186 series) would be joined by a sporty two-seater. This was developed almost in parallel and made its debut as the 300 S (W 188) at the Paris Motor Show in autumn 1951. Haspel toyed with the idea of putting it to sports use. In June 1951, he asked his chief development engineer Fritz Nallinger about the prospects of success. Nallinger’s unequivocal response was that there was little hope of success in racing using a passenger car chassis; these vehicles were too heavy and, at best, could only be used as touring cars. But as Haspel was dead set on involvement in motor sport, the project to develop a racing sports car was pursued further. The result was the Mercedes-Benz 300 SL (W 194).
Its M 194 engine was derived from the power plant of the 300, the M 186, with an inclined separation plane between cylinder head and engine block, overhead camshaft, large inlet valves, combustion chamber in piston and engine block, a displacement of 3 litres, and 115 hp (85 kW). For use in the racing car the engineers increased the engine’s output to around 170 hp (125 kW). The sports engine differed from those installed in the Saloon and Coupé not only in terms of output; it was also mounted differently, canted at 50 degrees to the left, and featured a dry-sump lubrication system, which enabled a lower installation height owing to the lack of oil sump.
The engine and transmission of the maturing W 194 offered few opportunities for weight savings. The same was true of the heavy steel axles borrowed from the 300 model. That left only the frame and the outer skin for any possible weight reductions. Another option for enhancing competitiveness was to make the body as aerodynamic as possible. Rudolf Uhlenhaut, at that time head of passenger car testing at Daimler-Benz, once again returned to his concept for a lightweight tubular frame, an idea he had worked on some years earlier.
The designers then carried the concept forward to its logical conclusion, creating an extremely lightweight, torsionally rigid space frame made up of slender tubes welded into triangles, the tubular elements of which were subjected only to tension and compression forces. In torsion tests, the spaceframe proved stiffer than the chassis of the pre-war W 154 formula racing car, which had marked a great step forward in its day. The entire frame weighed just 50 kilograms (110 lbs) and formed the backbone of the W 194. The success in weight reduction was dramatic: a 300 S tipped the scales at around 1780 kilograms (3924 lbs), whereas the 300 SL (W 194) weighed in at only 1100 kilograms (2425 lbs).
In addition to cutting weight to improve acceleration, Uhlenhaut also sought to cut frontal resistance to optimise top speed. To achieve this he canted the relatively tall, in-line, six-cylinder engine at 50 degrees to the left, additionally reducing the height by using a dry-sump lubrication system, which did away with the need for an oil sump as an oil reservoir. These measures gave the car a very low-slung bonnet.
The body of this first SL anticipated a number of features of later production sports cars. These included the flat racing car front end of the pre-war cars, with Mercedes star mounted on the radiator grille. The coachbuilders in Untertürkheim and Sindelfingen spared no effort with the aluminium body. Thanks to the canted position of the engine and the aerodynamic profile they strove to create, the car was very low, free of trim right down to the underbody, with a flat front end, intuitively rounded aerodynamic lines, recessed headlamps, and wheels entirely enclosed in the bodywork.
The coupé “greenhouse” was as narrow as possible, with a steeply raked windscreen that curved into the A-pillars. The elongated rear window flowed into the aerodynamic rear end. The result was a relatively small frontal area measuring 1.78 square metres. The drag coefficient was measured on a 1:5-scale model and found to be cd= 0.25 – and that without taking into account the realistic airflow through the engine compartment. But in retrospect this result proved to be rather over-optimistic. A wind tunnel measurement made on historic vehicles in January 2012 by Mercedes-Benz Classic showed a drag coefficient of cd = 0.38 for the W 194.
The car’s doors deserve a chapter all of their own: in order for the space frame to achieve the desired high rigidity, it had to be as wide as possible in the passenger cell area. This requirement led to the spectacular and later celebrated gullwing doors. In the earliest models, the door opening started at the waistline. Deeply recessed into the roof, the doors opened upwards, creating an image reminiscent of outspread wings. For this reason the car was dubbed “gullwing” by the North Americans and “papillon” (butterfly) by the French. Driver and passenger boarded the car from above.
In the sum of its design characteristics, the Mercedes-Benz 300 SL (W 194) was one of the most sophisticated technical products of its day. And with it was created a racing sports car that would dominate the 1952 racing season.