Back in 1964, Mercedes-Benz launched its top-range W100 limousine which featured a SOHC 6.3 litre V8 engine. However the hand-assembly of the limousine and its very high price limited the sale of the car, whilst the size and weight affected performance. In 1966 company engineer Erich Waxenberger transplanted the big V8 into a standard W109, creating the first Mercedes-Benz Q-car.
Despite the large size of the W109, the automaker claimed 0-62 mph (0–100 km/h) time of 6.3 seconds. Full-scale production began in December 1967. Claimed as the fastest production sedan (top speed of 229 km/h), the 300SEL 6.3, held this title for many years. West Germany's stringently applied trade description laws and figures resulted in these figures being under quoted. The 6.3 also introduced a new numbering scheme, whereby the model name described the parent model and the engine displacement was separate. This nomenclature was used by Mercedes-Benz until the introduction of the class system in 1993.
The Mercedes-Benz 300 SEL 6.3 was a large luxury car built by Mercedes Benz from 1968 to 1972. It featured the company's powerful 6.3-litre M100 V8 from the luxurious 600 limousine installed in the normally six-cylinder powered Mercedes Benz 300 SEL. The result was a nearly 2-tonne saloon with performance similar to most dedicated sports cars and American muscle cars of the era. At the time of its release it was the world's fastest four door car.
The car started out as a private venture in 1966 by company engineer Erich Waxenberger. His principle was simple: take the powerful 6.3 liter V8 Mercedes-Benz M100 engine from the luxurious 600 limousine, and fit it into the regular Mercedes-Benz W109 S-Class model which only had 6-cylinder engines at that time. The result was a nearly 2-tonne saloon with performance similar to most dedicated sports cars of the era. It is said that Rudolf Uhlenhaut, when invited to test drive the prototype, opened the hood at the first red light to find out how the big engine and its supporting equipment had been squeezed in there.
Surprisingly, the rather conservative company went ahead and launched the car into the marketplace at the Geneva Motor Show in March 1968, in order to make better use of the M100 engine production facilities. The 6,500 build of the 6.3 outnumbered the 2,700 build of the 600 by far.
What set this car apart from its contemporaries in the late 1960s though, was that it could cruise at over 200 km/h (124 mph) with 5 occupants in complete comfort within the body styled by Paul Bracq. Later, the company also fitted new, smaller V8 engines into the W109 series. The 300SEL 4.5 was only available in the USA, while the 280 SE 3.5 Coupé could also be ordered in Europe.
In 1975, the Mercedes-Benz 450SEL 6.9 was introduced as a 300SEL 6.3 successor with larger displacement, modifications to the equipment, and more power.
Air suspension, ventilated disc brakes on all four wheels, power windows, central locking and power steering all came standard. Air conditioning, power sunroof, writing tables (for rear seats), window curtains, audio tape deck and rear seat reading lamps were available as optional equipment.
6,526 of these vehicles were produced.