Mercedes-Benz 300SL - First Direct Injection

First Direct Injection

The 300SL's engine, canted at a forty-five-degree angle to the left to allow for a lower hoodline, was the same 3.0 litre straight-6 as the regular four-door 300. Fitted with a Bosch mechanical Gasoline direct injection system it had almost double the power of the original 86 kW (115 hp) carbureted version.

While not the first fuel-injected car - Mercedes engineers who had developed the principle for the DB 601 fighter aircraft engine had used fuel injection in the tiny 2-stroke Gutbrod they had designed after the War - it was the first to inject fuel directly into the cylinders. This innovation allowed 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.

The engine's maintenance requirements were high. 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 nor long enough to reach a temperature high enough to evaporate it out of the oil.

Exacerbating the problem were the large oil cooler as well as the large volume of oil (10 liters), both oriented more to racing than to street driving, which virtually guaranteed that the oil would not reach a high enough temperature. In practice, many street drivers would block off airflow through the oil cooler, and the recommended oil change interval was 1,000 miles (1,600 km). Operation of the clutch was initially very heavy, later roadsters having an improved clutch arm helper spring which reduced the pedal force. From March 1963 to the end of production, a light alloy crankcase was used on a total of 209 vehicles.

Aerodynamics played an important role in the car's speed, Mercedes-Benz engineers even placing horizontal "eyebrows" over the wheel openings to reduce drag. Unlike many cars of the 1950s, the 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 caused a considerable difference in handling depending on the quantity of fuel on board.