The Mercedes-Benz 300 SEL 6.3 impressively demonstrates all the qualities of a power saloon and was a German dream car when it premiered in 1968. Today, the 300 SEL 6.3 is regarded as a dream classic, precisely because of these strengths.
The 6.3-litre V8 signals its readiness with a soft growl when the key is turned. 250hp at 4000rpm encounter a kerb weight of 1780 kilograms – an excellent combination. A gentle nudge of the accelerator delivers the power, and within seconds the saloon is in its element on the clear country road. It seems to look forward to every bend, then accelerates effortlessly out of it and glides powerfully along the next straight.
The large steering wheel with its slim rim feels slightly unfamiliar at first, but thanks to servo assistance, it makes steering the “6.3” a highly pleasurable experience. The saloon not only impresses with its power and perfect controllability, but also with its outstanding comfort, generous spaciousness and a pleasant ambience.
No wonder that the 300 SEL 6.3, which rounded off the W109 series as the flagship model in 1968, set new standards at the time. It is regarded as the progenitor of all high-performance Mercedes-Benz saloon models.
The 300 SEL 6.3 celebrated its premiere at the Geneva Motor Show in March 1968. The press information summarised its attributes: “This model is probably unrivalled in its combination of maximum comfort and extraordinary performance. It meets the wishes of customers who expect above-average power and performance.”
The saloon closed the gap between the 300 SEL and the 600 (W100), from which the V8 engine of the 300 SEL 6.3 was adopted. The new model was claimed to occupy a peak position in the international lineup of Mercedes-Benz.
The technical data confirms the sports-car-like performance characteristics of the saloon – its top speed is 220km/h, it accelerates from 0 to 100km/h in 6.5 seconds, and it covers one kilometre from a standing start in 27.1 seconds.
“This makes it one of the fastest and most spirited series-production cars on the world market. Its particularly quiet and absolutely vibration-free running, the air suspension and the automatic transmission produce a level of ride comfort that leaves no wish unanswered,” the press information continued.
Externally, the saloon showed hardly any differences from the other models in the W108/109 series. Only the “6.3” lettering on the right side of the boot lid, twin halogen headlamps with the latest lighting technology and additional front foglamps distinguished the flagship model, which otherwise remained very discreet.
In the interior, a speedometer with a larger scale, a rev counter in the standard version and different positioning of the clock distinguish the “6.3” from the 300 SEL. The air suspension and automatic level control provide an excellent basis for the high-performance model, automatically adapting to changing loads. The spring travel and therefore the vehicle’s attitude remain constant – to the great benefit of ride comfort. Internally ventilated disc brakes all round ensure optimum deceleration.
The extensive standard equipment also includes power steering, a smoothly and rapidly shifting 4-speed automatic transmission, a locking differential, power windows and pneumatic central locking.
The muscular V8 engine with a displacement of 6333 cubic centimetres was adopted from the prestigious Mercedes-Benz 600 (W100) limousine with very slight modifications.
It has an eight-plunger injection pump with automatic cold-start and warm-up that takes into account the accelerator pedal position, engine speed, air pressure and coolant temperature. Fuel is injected into the intake manifold at high pressure by eight nozzles. This arrangement had proved very successful in all Mercedes-Benz SE models for years, and ensured efficient combustion.
The front frame section, transmission tunnel and floor assembly were modified to accommodate the engine in the W109 series.
The 300 SEL 6.3 originated as an idea by Mercedes-Benz test engineer Erich Waxenberger. In the 1960s, he recognised the potential of the V8 engine in the Model 600 for the W109 series. Initially without the knowledge of the head of passenger car development, Rudolf Uhlenhaut, Waxenberger constructed a test car.
Uhlenhaut could not be kept in the dark for long, however – sitting in his office, he heard the subdued growl of the prototype’s engine as it passed by, and immediately summoned Waxenberger for a report, whereupon he consented to further development work. Those who knew Uhlenhaut could imagine him smiling discreetly as he signed the official development order.
No wonder that, with its performance figures at sports car level, the W109 300 SEL 6.3 is regarded as the progenitor of luxurious and comfortable high-performance German saloons, and as the founder of a successful tradition that continues to this day.
A total of 6526 units were produced up to 1972. This comparatively large volume for the time marked the entry of Mercedes-Benz into the power saloon segment. This fascinating model has long since become a classic on the collector’s market. 
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