The development of the Mercedes-Benz 300 SL began in 1950, when Mercedes-Benz began to think about a return to racing. In June 1951, the Board decided to resume participation in racing events from 1952 on, and gave the final orders for the construction of the 300 SL. This car was not sold to the public, it was built just for racing.
Its M 194 engine was derived from the 300 type unit, the M 186, with an inclined separation plane between cylinder-head and engine block, overhead camshaft, large inlet valves, combustion chamber in engine block and pistons, a displacement of 3 litres and an output of 115 bhp (85 kW). For its use in the racing car the engineers increased the engine’s output to around 170 bhp (125 kW).
Weight savings were hardly possible with the engine and the transmission of the W 194 that was in the process of being created. And this was also true of the heavy steel axles which had also been taken from the 300 model. That left only the frame and the exterior skin for any possible weight-savings. Another possibility for enhancing competitiveness was to create a body as aerodynamic as possible.
Rudolf Uhlenhaut, at that time Head of passenger car research at Daimler-Benz, took up his idea of a lightweight tubular frame again, an idea he had entertained some years before. The designers then carried the concept forward to its logical conclusion, creating a lightweight, extremely torsionally rigid frame consisting of very thin tubes joined together to form triangles, whose tubular elements were only subjected to tensional and compressive forces. The entire frame weighed just 50 kilograms and became the backbone of the W 194, as well as the basis for the production version of the 300 SL (W 198 I) and for the successful 1954/55 racing and motor sports car.
The coachbuilders in Untertürkheim and Sindelfingen spared no effort with the vehicle 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 an elegant low bonnet line, intuitively round-shaped, with recessed headlamps and its wheels entirely covered by the bodywork.
The classic Mercedes-Benz radiator shape was replaced by a flat racing car front end analogous to that of pre-war cars. The Mercedes star dominated the radiator grille prominently. The coupé greenhouse was made as narrow as possible, with a strongly raked windscreen, curving towards the A-pillars. The large rear window flowed over into the aerodynamic rear end. The result was a relatively small frontal area: 1.8 square metres. A drag coefficient was measured on an 1-in-5 scale model and found to be cd = 0.25, and that, even without taking into account the realistic airflow through the engine compartment.
The doors are a chapter all of their own: in order to lend a space frame the desired high rigidity, it has to be as wide as possible in the passenger cell sector. This requirement led to the spectacular and later so famous gullwing doors. In the first cars, the door opening began at the waistline. The doors, deeply incut into the roof, opened upwards, creating an image reminiscent of outspread wings, for which reason the car was dubbed “gullwing” by the North Americans and “papillon” (butterfly) by the French.
On March 12, 1952, the Mercedes-Benz 300 SL racing sports coupé, unusually smooth and, at a height of just 1,225 millimeters, unusually low, was presented to the excited and stunned press on the motorway between Stuttgart and Heilbronn.
A total of ten Mercedes-Benz 300 SL W 194 series cars were built for the 1952 season. After the Le Mans race, it was planned to enter the SL in a sports car race on the Nürburgring. To shed as much weight from the competing cars, the engineers cut the roofs off three coupés without further ado. A fourth car had been set up as a roadster right from the start. To permit easy access, the section of the door extending into the side of the car was retained, and a small windscreen was mounted to deflect air and flying insects. This resulted in a weight advantage of 100 kilograms over the coupé.
The year 1952 was an extremely successful one for Mercedes-Benz racing cars: second and fourth places in the Mille Miglia; triple victory in the sports car race in Bern; double victory at the 24 Hours of Le Mans; quadruple victory in the sports car race on the Nürburgring. The last big adventure of the season was participation in the third Carrera Panamericana Mexico, a race over five days and eight stages, 3,100 kilometres through Mexico. Mercedes-Benz accepted the challenge and entered two coupés and two roadsters in this rally, all powered by engines with an output meanwhile boosted to 180 bhp (132 kW). Karl Kling with Hans Klenk and Hermann Lang with Erwin Grupp reaped a legendary double victory for Mercedes-Benz in November 1952 in this contest.
The Mercedes-Benz 300 SL was reengineered for the 1953 season. Its bodywork was now made from magnesium sheet, even lighter than aluminium. In the wind tunnel it gained – especially in its front section – not only a new face, but also a better airflow through the engine compartment thanks to an optimised shape. The engine output rose, too, among other things thanks to petrol direct injection, which boosted output of the six-cylinder unit to 215 bhp (158 kW). The rear axle was further developed to a low-pivot single-joint swing axle, while the transmission was flanged on the rear axle following the transaxle principle, which made for a more balanced weight distribution. The wheelbase was shortened by 100 millimetres. The vehicle stood firmly on 16-inch wheels, and the use of disc brakes was considered.
This further-developed Mercedes-Benz 300 SL with the company-internal designation W 194 (jocularly called “carpenter’s plane” on account of its front end), did not actually get to race. However, its bodywork with its angular radiator, compact dimensions and ventilation fins as well as its engine, prefigured in 1953 the W 198 I series 300 SL production sports car that was unveiled the following year.