After World War II, Daimler-Benz launched a motorsport programme intended to revive memories of the successful Silver Arrow racers of the Thirties. Chief engineer Rudolf Uhlenhaut - said to have been a very talented driver who had beaten Fangio’s lap times in testing - oversaw the construction of a lightweight tubular steel spaceframe chassis, consisting of grid-style tubing welded into a series of triangles, two large bulkheads each side for optimum torsional rigidity and independent coil-spring suspension.
The bodywork teams at Mercedes’ facilities at Unterturkheim and Sindelfingen produced a lightweight aluminium shell which demonstrated all the latest developments in aerodynamic theory, with integrated headlights and a low-riding stance; the finished prototypes had a drag coefficient of 0.25Cd, ground-breaking for the time. The light weight of the bodyshell compensated for the relatively heavy steel axles, developed from those of the 300-series production models of the time. Conventional doors could not be fitted, given the shape of the spaceframe construction, so a slightly awkward compromise was reached whereby a section of the coupe’s roof and framed window pivoted upwards and outwards for the driver and co-driver to scramble in and out.
The engine - a development of Daimler-Benz’s 2996cc straight-six also used in the 300 limousine and 300S coupe and cabriolet - was mounted at 50 degrees, giving a low centre of gravity and good weight distribution, as well as allowing for the long, low bonnet. This initial competition car’s engine, the M-194 unit, featured three Solex carburettors, overhead valves suspended in a V-shape from the cylinder head and an overhead camshaft; it was good for 175bhp and worked with an all-synchromesh four-speed gearbox. Interior comforts were sparse: this was a stripped-out racing car, not a boulevard cruiser.
Making its debut in 1952, the Mercedes 300SL - 300 to denote the 3.0-litre engine, SL "Sport Leicht", or "Sport Lightweight" - made an instant impact. Finishing in second and fourth places in the Mille Miglia thousand-mile road race of May ’52, a three-car team then made a clean sweep in the Bern Grand Prix before going on to take first and second places in the Le Mans 24 Hours, setting a new average speed record of 155.575kmph. Shortly afterwards, four SLs took the first four places in a race at the Nurburgring - the fourth car to finish being the first roadster prototype. Towards the end of the year, four 300SLs with their engines boosted to 3.1-litres and 180bhp contested the gruelling and notoriously dangerous five-day Carrera Panamericana race through Mexico, taking first and second places despite a series of accidents, punctures and the controversial disqualification of one car for alleged technical infringements. After such a successful year, Mercedes switched to focusing on its eight-cylinder W196 single-seaters for Grand Prix events, and the SL story could have ended there if it hadn’t been for the company’s US importer, Max Hoffman.
A race car for the street
The gullwing doors, hinged at the roof and so named because the open doors resembled a bird’s outstretched wings, were implemented as such to accommodate for the car’s tubular chassis, designed by DBAG’s chief developing engineer, Rudolf Uhlenhaut. Part of the chassis passed through what would be the lower half of a standard door. This tubular chassis was a necessity, as the original car was designed solely for racing and needed to be as light as possible while still providing a high level of strength. This required the driver and his/her passengers to do some gymnastics to get in or out of the car, usually by sitting on and sliding across the wide door sill. A steering wheel with a tilt-away column made the process considerably easier.
It was Max Hoffman, Daimler-Benz’s official importer in the USA, that convinced DBAG management in Stuttgart that a street version of the 300SL would be a commercial success, especially in the US. Hoffman’s prediction was correct since more than 80 % of the vehicle’s total production of approximately 1400 units were sold in the US, making the Gullwing the first Mercedes-Benz which sold in bulk outside its home market. The 300SL is credited for changing the company’s image in America from a manufacturer of solid but staid automobiles to that of a producer of sporty, even sexy cars.
Built completely with steel except for the aluminium bonnet (hood), doors and boot (trunk), the 300SL could have been ordered with an all-aluminium outer skin, saving 80 kg (176 lb) but at tremendous added cost.
First with fuel injection
The engine, canted at a fifty-degree angle to the left to allow for a lower hoodline, was the same 3.0 liter straight-6 as the regular four-door 300 but with a Bosch mechanical fuel injection system that more than doubled its power from 86 kW (115 hp) in its original carbureted trim to 180 kW (240 hp) at 6100 rpm. This new injection system, a first in any gasoline-powered car (apart from the rather small Gutbrodt where the Mercedes engineers had to work after the war), allowed a top speed of 260 km/h (161 mph) depending on gear ratio (several options), making the 300SL the fastest production car of its time. The maintenance requirements were high as, unlike the current electrically powered fuel injection systems, the mechanical fuel pump would continue to inject gasoline into the engine during the interval between shutting off the ignition and the engine’s coming to a stop; this gasoline was of course not burned, and washed the oil from the cylinder walls and ended up diluting the engine’s lubricating oil, particularly if the engine was not driven hard enough and long enough to reach a temperature high enough to evaporate it out of the oil.
Aerodynamics played an important role in the car’s speed. Mercedes-Benz engineers even went so far as to place horizontal "eyebrows" over the wheel openings. Given the car’s overall styling, it has been suggested that the eyebrows were added to make the car more appealing to American buyers rather than to serve any functional purpose since American cars of the period were rather flamboyant by comparison to the 300SL. Unlike many cars of the 1950s, the steering was rather precise and the four-wheel independent suspension allowed for a reasonably comfortable ride and markedly better overall handling. However, the rear swing axle, jointed only at the differential and not at the wheels themselves could be treacherous at high speeds or on imperfect roads due to extreme changes in camber.
Production stopped in 1963 after having produced 1.853 samples.
The 300SL is today a collector item with a very high price for a good specimen.