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W198 I 300SL Alloy Coupe
The Mercedes-Benz 300SL (W198) was the first iteration of the SL-Class grand tourer and fastest production car of its day. Introduced in 1954 as a two-seat coupé with distinctive gull-wing doors, it was later offered as an open roadster.
Built by Daimler-Benz AG, the direct fuel injected production model was based on the company's highly successful yet somewhat less powerful carbureted overhead cam straight 6 1952 racer, the W194.
The idea of a toned-down Gran Prix car tailored to affluent performance enthusiasts in the booming post-war American market was suggested by Max Hoffman. Mercedes accepted the gamble and the new 300 SL – 300 for its 3.0 litre engine displacement and SL for Sport Leicht (Sport Light) – was introduced at the 1954 New York Auto Show rather than the Frankfurt or Geneva gatherings company models made their usual debuts.
Immediately successful and today iconic, the 300SL stood alone with its distinctive doors, first-ever production fuel-injection, and world's fastest top speed. The original coupé was available from March 1955 to 1957, the roadster from 1957 to 1963.
New York Mercedes distributor Max Hoffman, Daimler-Benz's official importer in the USA, suggested to Daimler-Benz AG management in Stuttgart that a street version of the W194 Gran Prix racer would be a commercial success, especially in America.
The racing W194 300SL was built around a welded aluminum tube spaceframe chassis to offset its relatively underpowered carbureted engine. Designed by Daimler-Benz's chief developing engineer, Rudolf Uhlenhaut, the metal skeleton saved weight while still providing a high level of strength. Since it enveloped the passenger compartment traditional doors were impossible, giving birth to the model's distinctive gull-wing arrangement.
Even with the upward opening doors, the 300SL had an unusually high sill, making entry and exit from the car's cockpit problematic. A steering wheel with a tilt-away column was added to improve driver access.
The 300SL's main body was steel, with aluminum hood, doors and trunk lid. It could also be ordered with an 80 kg (176 lb) saving all-aluminium outer skin at tremendous added cost; just 29 were made.
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 widely successful outside its home market and thoroughly validating Hoffman's prediction. The 300SL is credited with changing the company's image in America from a manufacturer of solid but staid luxury automobiles to one capable of rendering high-performance sports cars.
Like the W194, the 300SL borrowed its 3.0 litre overhead cam straight-6 from the regular four-door 300 (W189 "Adenauer") luxury tourer introduced in 1951. Featuring an innovative diagonal aluminum head that allowed for larger intake and exhaust valves, it was canted to the right at forty-five-degrees to fit under the SL's considerably lower hoodline.
In place of the W194's triple two-barrel Solex carburators, a groundbreaking Bosch mechanical direct fuel injection was installed, boosting power almost 25% over the Gran Prix car's. Derived from the DB 601 V12 used on the high-powered Messerschmitt Bf 109E fighter of World War II, it raised output from 175 hp (130 kW) to 215 hp (160 kW), almost double that of the original Type 300 sedan's 115 hp (86 kW).
The result was a top speed of up to 260 km/h (161 mph) depending on gear ratio and drag, making the 300SL the fastest production car of its time. However, unlike today's electrically powered fuel injection systems, the 300 SL's 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 unburned gasoline washed lubricating oil from the cylinder walls, which not only left them unprotected in affected areas during start-up but would dilute the engine's entire oil supply if the car was not driven hard or long enough to reach a sufficient temperature to evaporate the gas out of the oil.
Exacerbating the problem was the engine's large racing-oriented oil cooler and enormous 10 liter oil capacity, which virtually guaranteed the oil would not get hot enough. In practice, many owners would block off airflow through the oil cooler and stick rigidly to the appropriately low 1,000 miles (1,600 km) recommended oil change interval. Clutch operation was initially very heavy, remedied by an improved clutch arm helper spring which reduced pedal force. From March 1963 to the end of production later that year, a light alloy crankcase was used on a total of 209 vehicles.
Aerodynamics played an important role in the car's speed, with Mercedes-Benz engineers placing horizontal "eyebrows" over the wheel openings to reduce drag. Unlike many cars of the 1950s, steering was relatively 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, not at the wheels themselves, could be treacherous at high speeds or on imperfect roads due to extreme changes in camber. The enormous fuel tank capacity also caused a considerable difference in handling depending on the quantity of fuel on board.
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