Mercedes-Benz 300 SLS (W 198), 1957
As the successor to the "Gullwing", a roadster version of the 300 SL made its debut in March 1957, as requested by importer and sales partner Max Hoffman from the outset. This model was made possible by a revision of the tubular frame, which was now lower in the entrance area and therefore no longer prevented the use of normal, side-opening doors. Although still very powerful, the roadster had a different character to its predecessor: Less Spartan-sporty than the "Gullwing", it was designed more for comfort – an aspect that was also reflected in its higher weight.
The roadster therefore seemed less suitable for a motorsport career, but this was not seen as a handicap after Daimler-Benz announced its official withdrawal in October 1955. The fact that things turned out differently, however, was mainly due to sales activities in the USA. Towards the end of 1956, the Curtiss-Wright company emerged as a future sales partner – at the time an American manufacturer of aircraft engines that had recently entered into a joint venture with the ailing Studebaker-Packard Corporation. The new partner expected Daimler-Benz to be involved in motorsport in the USA in order to utilise the racing successes of the Stuttgart-based company to promote the sales of Mercedes-Benz vehicles.
At the end of November 1956, the Daimler-Benz Board of Management agreed and decided to make two modified 300 SL Roadsters available for racing. The result was a fundamentally revised special version, known internally as the 300 SLS (SL Special). This further development was necessary in order to make the roadster competitive through a more favourable power-to-weight ratio. The production version would also have been out of the question because the "Sports Car Club of America" refused to approve the brand-new model for the 1957 season in the "Standard Production" category, as it was unlikely that the number of 150 vehicles produced and sold required for homologation would be reached.
The standard roadster was slimmed down by every trick in the book so as not to be left without a chance in the only possible alternative racing category D. These included the use of an aluminium body, the omission of bumpers, a lighter engine with an aluminium engine block and various weight-reduced components, a clutch housing made of electron, components such as the tank, auxiliary tank and steering column made of aluminium, a racing car steering wheel, a side-exiting exhaust system and a specially made cockpit fairing with a small racing windscreen. The only weight-increasing factor was the roll bar behind the driver's seat. In the end, the SLS weighed in at just 1040 kilograms – 290 kilograms less than a standard roadster.
After the weight-shedding treatment, the engine weighed just 184.5 kilograms – also a very significant saving compared to the 256 kilograms of the standard engine with grey cast iron block. With larger valves, optimised combustion chambers, a higher compression ratio and two individual exhaust pipes exiting to the side, it was possible to increase the engine output to 235 hp/173 kW at 5900 rpm. Nevertheless, the racing engine was a paragon of reliability: In the 16 races of the 1957 season in which O'Shea took part with the SLS and which counted towards the championship, there were five wins, six second places and one fourth place, but only four retirements, none of them due to engine problems. In the end, Paul O'Shea won the American Sports Car Championship in category D for the third time in a row with a clear lead over the competition.