Mercedes-Benz 450SEL 6.9 Was All About Engineering

Editor’s note: This article originally appeared on Sept 30, 2014, we’ll be diving into our archives to bring you some of the gold you might have missed from our early days.

Photography by Rémi Dargegen

It is hardly possible to overstate the grimness that prevailed thirty-seven years ago when the 1977 Mercedes-Benz 450SEL 6.9 came the United States. The nation seemed to be inextricably in OPEC’s grip, the so-called federalizing of automobiles was in full swing, and John DeLorean was just revealing his strange sports car as The Answer. Even worse, K.C. and the Sunshine Band kept singing “I’m Your Boogie Man.”

Yet going back even beyond Nixonian times, the horsepower wars being fought in Detroit had captivated the Germans. The Mercedes-Benz 300SEL 6.3, made from 1968 to 1972, was engorged with the V-8 from the 600 limousine, becoming the grandfather of all the German sports sedans. Meanwhile, in the five years between its discontinuation and the appearance of this new sedan, emissions controls were choking carbureted cars. Even the Chevrolet Corvette was hitting singles instead of home runs.

Just in time, the world’s fastest production four-door sedan dropped by to say guten tag for $38,230, an outrageously expensive price for a car that someone like Mr. Lee Iacocca would have condemned for its lack of velour. It had hard leather seats, a godawful slab of wood on the dash, and few other amenities. Slightly wider fourteen-inch wheels and a 6.9 emblem on the trunk lid distinguished it from the garden-variety 450SEL. What you were paying for wasn’t flash, it was engineering. And the engineering started under the hood.

A few large American sedans had big-block engines before new emissions regulations pretty much killed them off, but nothing was as sophisticated as the hand-built SOHC 6.9-liter V-8 in the 17.5-foot-long Mercedes’s engine bay. The displacement was achieved by boring out the 6.3-liter engine to 6834 cc. Mechanical fuel injection helped with U.S. certification, although at 10 mpg in the city and 14 mpg on the highway, efficiency could never be claimed. To aid with packaging and maintain the low hood line, the V-8 had a dry sump. The oil reservoir in the right-front corner held the 12.7 quarts necessary to satisfy internal flow requirements; an incidental benefit was the oil change interval of 12,500 miles or once a year, whichever came first.

Other sophisticated touches included the engine’s aluminum cylinder heads in an era when cast-iron still ruled. Sodium-filled exhaust valves encouraged heat dispersion. This was neither a high-compression V-8 at 8.0:1, nor a high-revving one: it generated 250 hp at 4000 rpm and redlined at 5000 rpm. Torque output of 360 lb-ft made itself felt at 2500 rpm. (Horsepower and torque were about 12- and 11-percent reduced from the European version.) A three-speed automatic transmission brusquely managed the torque, sending it via a limited-slip differential to the rear wheels. Dashing from 0 to 60 mph required 7.1 seconds, and top speed was 133 mph.

The engineers also devoted themselves to ride and handling, so the 6.9 was outfitted with a hydropneumatic suspension that compensated when the accelerator or brake pedal got stomped. Oil was pumped in and out of a strut at each corner, as required to meet variations in load, and this hydraulic action combined with a stored supply of nitrogen to effect damping and springing; the self-leveling was a related benefit for the 4390-pound car. Stiffer front and rear stabilizer bars countered body roll.

Electronic controls for the powertrain, suspension, and chassis were for the future. Meantime, the 450SEL 6.9 represented the high-water mark for purely mechanical efforts to motivate and regulate a big beast. In his thorough review for Car and Driver, Mr. David E. Davis, Jr. noted the complexities and imperfections but called the car “an exclamation point on the story of an entire automotive era.” Given the bleakness of the time, Davis certainly could not be blamed for failing to foresee such amazements as the BMW 740i and 750i, which would come in a generation. All he knew was, whereas the 300SEL 6.3 had creaked, the 450SEL 6.9 crowed.

Now one of the most highly prized and collectible sport sedans ever, the 6.9 was manufactured until 1981, and a substantial number of the 7380 units have ended up in the U.S. Buying one doesn’t require an arm and a leg, as the very best examples don’t generally crack the $50,000 barrier. Besides cash, all the buyer will need is the number of a good mechanic.

Thank you to Montfort Automobiles for allowing us to photograph their Mercedes-Benz.