S-Class: The W109 6.3, W116 6.9, W126 560 & W140 600
The S-Class W109 300 SEL 6.3, 1968–1972.
Its power was equal to that of a high-level sportscar
In March 1968 the 300 SEL 6.3 became top of the class of this model series. It was equipped with the V8-engine and the automatic gearbox of the 600 model so that its power was equal to that of a high-level sportscar.
Many customers were interested in the 300 SEL 6.3
Its presentation at the Geneva Motor Show created a sensation, especially since there had been no hints, that a model like this was to be forthcoming. From outside, the 6.3 could only be recognised by its broader tires, double halogen headlights and additional distance beam headlights.
Even though it cost over DM 10,000 more than a 300 SEL and twice as much as the 280 SE, many customers were interested in the 300 SEL 6.3, so that 6,526 units were produced.
The S-Class W116 450 SEL 6.9, 1975-1979.
In May 1975 Type 450 SEL was presented as the new top model of the Type range and as the legitimate successor to 300 SEL 6.3. The powerful 6.9-liter V8-engine ( ), developed from the 6.3-liter unit, achieved 286 hp and a maximum torque of 56 mkg.
For the first time in a Mercedes-Benz car a hydropneumatic suspension with level control system guaranteed highest driving comfort. Further optional equipment belonging to the production delivery of the top model included central locking system, air-conditioning and headlamp washer system.
The 450 SEL 6.9 was an immediate and full success
As its direct predecessor, the 450 SEL 6.9 was an immediate and full success. Even though it was more than twice as expensive than the 350 SE, as many as 7,380 cars were built within its production time of four years.
The S-Class W126 560 SEL, 1985-1991.
September 1985, again at the Frankfurt show, a completely revised S-Class range was introduced. In addition to a subtle facelift, which mainly altered the appearance of the bumpers, side skirts and wheels, the emphasis was on a restructured engine line-up. The most spectacular innovation in the engine range was a 5.6-litre eight-cylinder unit.
A 5.6-litre eight-cylinder unit
The most spectacular innovation in the engine range was a 5.6-litre eight-cylinder unit, which was developed by lengthening the stroke of the 5.0-litre V8 and which unleashed an output of 272 hp. If required, an even more highly compressed version was also available that delivered a mighty 300 hp, although it was not possible to combine this unit with a closed-loop emission control system. But even without a catalytic converter this ‘ECE version’ met the emissions standards stipulated by the Economic Commission for Europe. The models fitted with this engine variant – the 560 SEL and 560 SEC – were, in their day, the most powerful Mercedes-Benz production cars ever built.
“The 560 SEL and 560 SEC – were, in their day, the most powerful Mercedes-Benz production cars ever built”.
All variants in the revised model range – with the exception of the 560 SEL and 560 SEC in the ECE version – were available on request with a closed-loop emission control system with three-way catalytic converter. In each case the series version was the ‘catalytic converter retrofit version’, for which the vehicle was delivered without catalytic converter and oxygen sensor, but with the multi-functional mixture preparation and ignition system. These retrofit versions could be fitted with the closed-loop catalytic converter without difficulty at a later date. This gave customers maximum flexibility in choosing the time to convert their vehicle – a not insignificant advantage, given that unleaded petrol was not universally available at the time.
The closed-loop catalytic converter
From September 1986, the closed-loop catalytic converter was standard equipment on all Mercedes-Benz passenger car models with petrol engines; the retrofit versions were available until August 1989 – with a corresponding price discount.
The most successful premium-class series in the history
Production of most variants came to an end between August and October 1991, although the last few armoured models did not come off the production line until April 1992. During the entire twelve-year production period a total of 818,036 saloons left the production lines in Sindelfingen, 97,546 of them with diesel engines. That made the 126 the most successful premium-class series in the history of the company.
In March 1991 the new S-Class generation (designated internally as the 140 series) made its debut at the Geneva Motor Show. The production of the 6.0-litre V12 engine model began in February 1992, one year after main production start-up for the 140 series.
The 6.0-litre V12 M 120 engine was an entirely new design. Not only was it the first twelve-cylinder Mercedes-Benz made for a production passenger car, but it was also the most powerful Mercedes-Benz car engine of its day, with a rated power output of 300 kW (408 hp). With a peak torque of 580 Newton metres, it reached the 500 Newton metres mark at 1600 rpm.
As with the six-cylinder and the two V8 engines, the twelve-cylinder was also equipped with four-valve technology, variable intake camshaft and an electronic injection system with hot-wire air mass sensor. With all engines a high priority was placed on minimising exhaust emissions and reducing fuel consumption.
The new fully electronic ignition system calculated the optimum ignition point from 300 ignition maps, tuned for each cylinder individually and to the knock limit in each case. The M 120 was the only twelve-cylinder engine in the world to feature this cylinder-selective anti-knock control.
Without this it would not have been possible to achieve the high compression ratio of 10:1, necessary for optimum use of fuel.
The engine management and drive management were also completely new. All their control modules communicated with one another via a common data channel, meaning the control units could all be active at the same time. This was used for rapidly warming up the catalytic converters when cold-starting the engine, as well as for acceleration skid control and for the new engine friction torque control, which maintained handling stability during power-off situations on slippery road surfaces.
The V12 offered the world’s largest catalytic converter unit for passenger cars. Its seven-litre volume avoided any excess fuel consumption on account of the catalytic converter and ensured a high degree of long-term stability.
Thanks to an innovative concept involving a double-walled and triple-insulated exhaust manifold, as well as double-walled pipes, the ceramic catalytic converters – embedded in insulating expandable matting – reached the optimum operating temperature in a very short time.
8,573 6.0-litre V12 M120 engines where build in Baureihe W140.
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