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W116 450SEL 6,9
The Mercedes-Benz 450SEL 6.9 is the high-performance top-of-the-line version of the W116 model S-Class luxury saloon. It was built by Daimler-Benz in Stuttgart, Germany and based on the long-wheelbase version of the W116 chassis introduced in 1972. The model was generally referred to in the company's literature as the "6.9", to separate it from the regular 450SEL. It featured the largest engine of any non-American production car post WWII.
The 6.9 was first shown to the motoring press at the Geneva Auto Show in 1974, and produced between 1975 and 1981 in extremely limited numbers. It was billed as the flagship of the Mercedes-Benz car line, and the successor to Mercedes-Benz's original high-performance sedan, the 300SEL 6.3. The 6.9 also has the distinction of being among the first vehicles ever produced with optional electronically controlled anti-lock brakes, first introduced by Mercedes-Benz and Bosch in 1978.
The 6.9's successor (since 1985) — the top of range 560 SEL — continued the 6.9's self-leveling hydropneumatic suspension as an extra-cost option. Active Body Control is the current iteration of this innovation.
The 6.9 was the first Mercedes-Benz to be fitted with the hydropneumatic self-levelling suspension system introduced by Citroën in 1954, unlike the 600 and 6.3 which employed air suspension.
The benefit of this arrangement is progressive springing. The more the enclosed air in the suspension is compressed, the more difficult it is to compress; thus the suspension rate changes in proportion to the load.
Using a combination of fluid-filled struts and nitrogen-filled pressure vessels or "accumulators" in lieu of conventional shock absorbers and springs, the system was pressurized by a hydraulic pump driven by the engine's timing chain. Compared to the new Mercedes-Benz system, Citroën's was belt-driven, exactly like a conventional power steering pump; failure of the Citroën system thus might result in loss of suspension. The 6.9 was shipped with hard rubber emergency dampers that served as temporary springs and allowed the car to be driven in the event of a hydraulic failure. The special hydraulic fluid required by the system was stored in a tank inside the engine compartment. Ride height could be altered by a dash-mounted push-pull knob under the speedometer that raised the car an additional two inches (50 mm) for increased ground clearance.
The suspension system gave the 4200 pound (1900 kg) car the benefits of both a smooth ride and handling that allowed it, in the words of automotive journalist David E. Davis, to be "tossed about like a Mini." The car also featured a model W3B 050 three-speed automatic transmission unique to the 6.9 and a standard ZF limited slip differential both for enhanced roadholding performance on dry pavement and enhanced traction in inclement weather.
Four-wheel disc brakes and four-wheel independent suspension were standard across the W116 model range.
The engine was a cast iron V8 with single overhead camshafts operating sodium-filled valves against hardened valve seats on each aluminum alloy cylinder head. Each hand-built unit was bench-tested for 265 minutes, 40 of which were under full load. Bosch K-Jetronic electromechanical fuel injection was standard at a time when fuel-injected cars were uncommon. As in all Mercedes-Benz automobile engines, the crankshaft, connecting rods and pistons were forged instead of cast. The 6.9 l (6834 cc or 417 in³) power plant was factory-rated at 286 hp (213 kW) with 405 lb·ft (549 N·m) of torque helping to compensate for the 2.65 to 1 final drive ratio necessary for sustained high-speed cruising. A special version for Australia, based on the North American version, however without catalyst, was rated at 269 hp (198 kW) with 51 kpm (510 N·m) of torque. In the interest of both engine longevity as well as creating some extra space under the hood, a "dry sump" engine lubrication system was used. The system circulated twelve quarts of oil between the storage tank and the engine, as opposed to the usual four or five quarts found in V8s with a standard oil pan and oil pump. As a result, the engine itself had no dipstick for checking the oil level. Rather, the dipstick was attached to the inside of the tank's filler cap (accessible from the engine compartment) and the oil level was checked with the engine running and at operating temperature. The dry sump system also had the benefit of extending the oil change interval to 12,500 miles (20,000 km). This, along with hydraulic valve lifters which required no adjusting and special cylinder head gaskets which eliminated the need for periodic retorquing of the head bolts, made the 6.9 nearly maintenance-free for its first 50,000 miles (80,500 km). The 6.9 required little basic service other than coolant, minor tune-ups, oil changes, and replacement of the air, fuel, oil and power steering filters.
The 6.9 lacked expected luxury touches such as power-adjustable outside mirrors or front seats, although a unique power rear seat, heated seats and even orthopedically designed front seats were options. There was also a new standard feature in 1976: most Mercedes-Benz automobiles that year were equipped with a sophisticated electronic climate control system developed by Chrysler Corporation for use in their top models. The system turned on the heater, air conditioner or both, depending on the thermostat's setting and ambient temperature, automatically maintaining whatever temperature the driver selected. The compressor was an American import as well, supplied by the Harrison division of General Motors.
The interior was identical to that in the less expensive models except for the push-pull suspension control knob just under the speedometer, a low suspension pressure warning and height adjustment indicator lights in the instrument cluster, and wood trim finished in burled walnut veneer on the dash and console. The rest of the W116 lineup was trimmed in striated zebrano veneer.
Being the top-of-the-line offering in its brand and model lineup, the 6.9 was rather indistinguishable from its W116 stablemates save for a modest "6.9" badge on the decklid and wider tires. The badge could be deleted/ordered with option No. 261 i.e. omission of the displacement figure on the trunk lid at extra cost from the factory. In the words of David E. Davis, the 6.9 was "a $50,000 exercise in going fast."
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