Mercedes-Benz 450SEL 6.9
The 450 SEL 6.9 is the high-performance version of the W116 S-Class saloon. It was based on the long-wheelbase version of W116 chassis introduced in 1972 and equipped with Mercedes-Benz M100 V8 engine and full hydropneumatic suspension system. The 450 SEL 6.9 was presented to the public at the Geneva Auto Show in 1974 as the successor to the original high-performance saloon from Mercedes-Benz, the 300 SEL 6.3 (1968–1972). Like 300 SEL 6.3, the nomenclate, 6.9, was affixed to the trunk lid as to differentiate itself from 450 SEL. The  450 SEL 6.9 was produced in a very limited number from 1975 to 1981. The 450 SEL 6.9 had the first full hydropneumatic suspension system from Mercedes-Benz and was the world’s first passenger car to be fitted with modern form of ABS, electronic four-wheel multi-channel anti-lock braking system from Bosch, in 1978. For several years, the 450 SEL 6.9 was the quickest-accelerating and fastest European saloon, reaching in 7.4 seconds and top speed. The direct successor of 450 SEL 6.9 is the 2003 Mercedes-Benz S 55 Kompressor AMG (W220, 2003–2005), given the criteria  that they were built in limited production and had unique 5.4-litre engine with supercharger not shared with S 500. Mercedes-Benz had claimed 500 SEL (W126) to supersede 450 SEL 6.9 in its 1980 brochure despite 500 SEL being in regular production and sharing the same M117 engine with 450 SEL. S 70 AMG and S 73 AMG (W140, 1998–1999) were the commissioned models for the clients who requested the performance upgrade kits to the engine, chassis, and body. The total production from 1975 to 1980 was 7,380 units with 1,816 exported to the North American markets (United States  and Canada) from 1977 to 1981. M100 engine. The 6.3-litre M100 V8 engine, originally fitted to 600 and 300 SEL 6.3, was enlarged to 6.8 litres (6,834 cubic centimetres or 417 cubic inches) by boring out to 107 mm. The stricter emission regulations in the mid-1970s necessitated the larger displacement as to compensate for the lowered output. The fuel injection system was upgraded to the third-generation mechanically controlled, continuous-injection system Bosch K-Jetronic. Due to its sheer size, the engineers fitted the dry sump oil lubrication system as to lower the engine height and preserve the low  hood line. The dry sump system had larger capacity at 12 litres rather than 5 litres for the wet sump system fitted to the smaller M116 and M117 V8 engines. The dipstick was moved from the engine block to the oil tank’s filler cap. The larger oil capacity extended the oil change interval to 20,000 km (12,500 miles). For the European and international markets, the M100 engine produced at 4,250 rpm and at 3,000 rpm. The 450 SEL 6.9 for the North American markets had the reduced output and compression ratio (8.0:1 instead of 8.8:1) and was fitted with  catalysator that required lead-free petrol: at 4,000 rpm and at 2,500 rpm. The 450 SEL 6.9 sold in Australia had slightly reduced output due to Australia's new 1977 emission regulations: at 4,200 rpm and at 2,800 rpm. During its entire production run, the engine displacement of 6.8 litres was the largest V8 engine ever built by Mercedes-Benz and by European manufacturer after the Second World War. Suspension. The full hydropneumatic self-levelling suspension system from Mercedes-Benz was first introduced in 450 SEL 6.9 as a standard equipment. The other W116 models used the hydropneumatic system for  the rear suspension only as level control under heavy load (Option No. 48/0, "Niveauregulierung"). The full system was exclusive to 450 SEL 6.9 until 1981 when the next generation, HPF II, was offered as an extra-cost option for W126 380 SEL and 500 SEL. The 600 and W109 used the air suspension for self-levelling. The Mercedes-Benz system differentiated from Citroën system, introduced in 1954, in some ways. Mercedes-Benz used the timing chain to drive the hydraulic pump instead of rubber belt in Citroën system. Citroën system used a single pump to send the vegetable oil (and  later mineral oil) to the brake boost, power steering, power clutch (when equipped with semi-automatic transmission), and hydropneumatic suspension system. Mercedes-Benz system had the separate pumps for brake boost, power steering, and hydropneumatic suspension, citing the better failsafe measures than Citroën in the event of a hydraulic failure. The Mercedes-Benz system contained the hard rubber dampers that served as temporary springs and allowed the car to be driven if the hydraulic pump or components failed. Both manufacturers had different approaches when the cars were parked and switched off. Citroën lowered themselves closer to the ground while Mercedes -Benz did not. Mercedes-Benz suspension system has the feature that maintain the body level without squatting at the rear or diving in the front during the acceleration and braking respectively. North American Market. Initially, Mercedes-Benz did not plan on selling the 450 SEL 6.9 in the United States given the oil crisis that hit the Americans very hard and increasingly tightening emission regulations. Mercedes-Benz had difficulties in meeting the European demand. However, the strong requests from the customers and dealers reversed the decision. For the United States market, 450 SEL 6.9 was marketed simply as 6.9 and  as sole affixation to the trunk lid on the right side. The retail price was more than $38,230 ($177,554 adjusted for 2021) for the 1977 model year and increased to $52,995 ($185,071) at the end of production in 1980. The 6.9 was fitted with four sealed beam 5.75" round capsule headlights with bezels and larger impact absorbing bumpers that lengthened the length by 11 inches. Due to the US FMVSS bumper standard, the variable height suspension was disabled, and the height adjustment knob was removed. To differentiate the 6.9 from other W116 models, the bumpers had  thicker black rubber stripe covering the entire width and without the rubber bumper guards. The engine output was reduced to and due to the stricter emission standards. Price. The retail price of 450 SEL 6.9 was DM 69,930 at its launch in 1975 and was DM 81,247 at the end of its production in 1980. The 450 SEL 6.9 had the premium of DM 25,000 to 30,000 over 450 SEL. While 450 SEL 6.9 was visually indistinguishable from the other W116 models, 450 SEL 6.9 had wider wheels and tyres along with 6.9 on the right side of trunk lid . 450 SEL 6.9 had more standard features that were extra cost options in other W116 models: automatic HVAC system, power windows, power rear seats, headrests for the rear passengers, central locking system, headlamp washer and wiper system, heat-insulating glass, and a few other equipments. Interior features. Despite the higher retail price, the interior of 450 SEL 6.9 was indistinguishable from the other W116 models except for the different type of wood trims, height adjustment knob, and two extra warning lamps in the instrument cluster for the low suspension pressure warning and height adjustment indicator. The heated seats for driver  and front and rear passengers as well as electric sunroof were extra cost options. No power-assisted external rear view mirrors and seat adjustments, commonly fitted to the luxury cars such as Cadillac and Rolls-Royce during the 1970s, were ever offered in the 450 SEL 6.9. The first-ever automatic HVAC system from Mercedes-Benz was introduced in the 450 SEL 6.9 as a standard equipment and as optional extra-cost equipment in other W116 models. The automatic HVAC system was adapted from Chrysler Corporation and had the compressor from Harrison division of General Motors. The 450 SEL 6.9  had the exclusive wood trim finished in burled walnut veneer on the dash and console instead of striated zebrano veneer as found in other W116 models.