Road test drive – Mercedes-Benz 300SEL 6.3 W109 and its successor 450SEL 6.9 W116

Which is the best hot-rod Benz? It’s like picking a favourite child for Martin Buckley, as he compares the two most potent Stuttgart muscle cars, the Mercedes SEL 6.3 and 6.9. Because they share a Big-Block engine and a certain ‘factory hot-rod’ sensibility, it has always felt natural to talk about the Mercedes-Benz 300SEL 6.3 W109  and its successor the 450SEL 6.9 W116 in the same breath. But when you have the opportunity to jump from one car to the other, you start to wonder just how similar they really are. Fairly evenly matched against the clock in terms of urge, yes, yet the earlier vehicle is as raw and thrilling as the later one is suave and accomplished. The thoroughly engineered 6.9 is much more what you expect of a Mercedes- Benz, whereas the 6.3 feels like an anomaly, the product of a series of happy accidents.

From top: the 6.3 is remarkably agile for a car of its size; 450SEL 6.9 loses out to the earlier car in pure performance, but is crushingly competent.

In its defence, Daimler-Benz AG of Stuttgart has never tried to pretend otherwise. Yet the oft- recounted story of development engineer Erich Waxenberger slipping a ‘spare’ 600 engine into a ‘spare’ W109 shell in his own time rings more hollow with every retelling, unless you happen to believe that a firm run along severe, almost military lines would allow a relatively junior engineer to get away with building a special. The truth about the creation of the most exciting Mercedes of the ’60s is simply that the huge and forbidding 600 wasn’t selling in anything like the numbers envisaged, and consequently the board was looking for ways to amortise development costs and use spare production capacity by finding a second home for its 250bhp V8.

Clockwise: cabin is among the last of the ‘classic era’; complex mechanical fuel injection; huge rear bench; ride is soft, with plenty of roll; four-speed auto.

Enter, in 1968, the 300SEL 6.3 saloon, a sales and image-building success story for a company that was beginning to lose its reputation as king of the autobahn under an assault from quick new cars from BMW and Opel. Based on the air- suspended long-wheelbase W109 shell – which had previously had nothing more potent than a 170bhp straight-six to propel it – the 300SEL 6.3 had more acceleration than had ever been available in a saloon before; enough to humble any 911 of the time and most road going Ferraris.

Everyone loved it, particularly the Americans – “Road & Track” famously subtitled its road test: ‘Merely the greatest sedan in the world. In Europe, the 6.3 was the favoured road transport for half of the grid at most Formula 1 meetings. There was simply nothing else quite like it.

When production of the 6.3 ended in 1972, a replacement was eagerly anticipated as part of the new W116 S-Class range, but initially V8 thrills only extended as far as the 4.5-litre unit in the long-wheelbase shell with ordinary steel springs. In fact, Mercedes had the 450SEL 6.9 ready for the market in 1974 but decided to delay the introduction until May 1975, thus avoiding the worst of the public relations fallout from launching a 145mph, 14mpg boardroom express in the aftermath of the fuel crisis.

The W116, with its trademark double bumpers and big dirt-resistant tail-lights, was stronger but necessarily heavier model-for- model than the old S-Class, with greater roll-over stiffness and side-impact protection. Apart from the badge on the bootlid and the wider tyres, the 6.9 was visually identical to the 450SEL and thus satisfied those who enjoyed the covert nature of the older car.

But Daimler-Benz was not of a mind to sanction another hot rod; if the 6.3 had been an uncouth motor car by Mercedes standards in certain matters, then it was immediately evident just by reading the specification that this new SEL was a more thoroughly designed machine, created from the start to take the big M100 engine – by then bored out to 6.9 litres and featuring a dry sump (to keep the bonnet line low) and hydraulic tappets. Another significant improvement was a change from frighteningly complex and expensive mechanical fuel injection to the all-new, Bosch-designed low-pressure continuous-flow K-Jetronic system.

Power was up from 250 to 286bhp, and on 98-octane fuel with its 8.8:1 compression ratio the heftier, higher-geared 6.9 didn’t have quite as much acceleration as the 6.3, but 0-60mph in 7.3 secs was still immensely quick for a car of this size. Perhaps more importantly, it could cruise faster than the older car – and it was probably of more than academic interest that it had another 11mph of top speed in hand. At 140mph, the 6.9 was pulling just 5000rpm and independent tests of European-specification cars regularly recorded top speeds of close to 150mph. To put the 6.9 fully into context, it had roughly comparable performance to a Maserati Khamsin and could keep in touch with uncompromising sports cars such as the Lancia Stratos, the Ferrari 308GTB and the Porsche 911 Carrera.

This new car had to be about more than just speed, of course. Additional technical refinements were required to justify the model’s existence and huge price-tag. Improved suspension – something to give it an additional dimension of luxury over and above the standard 450SEL – was the obvious answer, but what Mercedes couldn’t do was revisit the unreliable air-spring system as used on the 6.3. So for the 6.9 the coil springs were thrown away and replaced by gas-filled reservoirs connected by hoses to damper units. Pressure – 2100-2900psi -was applied by a small accumulator identical in design to the spring units and controlled by valves that were in turn actuated by linkages to the front and rear anti-roll bars. The gas behaved like a progressive spring, becoming harder the more it was compressed, while the amount of oil in the system determined the ride height.

Mercedes was quite proactive in getting F1 drivers into 6.9s as road transport, in the days when most of them still drove themselves to circuits. Tellingly, the 6.9 was the preferred transport of the likes of Emerson Fittipaldi, Niki Lauda, Ronnie Peterson and – most famously – James Hunt, who had two.

Ian Keers, chairman of the Mercedes-Benz Club, can trump all of the above, however, because he owns both a 6.3 and a 6.9. He acquired the beautifully original silver 450SEL from its first owner in 2005, and has doubled the mileage since then to 44,000. Keers says that it’s the cheapest car to run that he owns – but then his other car is a 6.3…

And the 6.3 in question, sold new in Glasgow in 1969, came along as a ‘running project’ in 2007, its mid-blue paint bubbling in places (it has since had a bare-metal repaint). Keers has suffered the usual expensive problems with the air suspension but, its owner having chased through the system replacing ‘O’ rings, air bags and valves, the 6.3 now retains its ride height even when left unused for long periods.

Of the two I find it much the prettier – so simple and slender-yet the 6.9’s authoritative shape looks better with every passing year. The W108/W109 saloons dating from 1965 are always pleasing places to sit, with their low window sills and great visibility. The 6.3 has a slim, large-diameter plastic steering wheel and broad seats with low backs: somehow your neck feels vulnerable without the optional head restraints. In the 6.9, the seats are more figure- hugging, the steering wheel almost as big but with a fat and grippy padded rim, the ridges still well defined thanks to this car’s low mileage. Both cars have multi-function column stalks, but the W116 is a product of the science of ergonomics, with clear views across the rational heater controls, three large main instruments and the typical Mercedes light switch operating the powerful Bosch head- and foglamps behind their rectangular covers.

There is a good view out of the 450SEL, but it’s not in the airy league of the W108; the hefty safety pillars of the W116 shell were a portent of the gloomily enclosed cabins of today. There is much more plastic to be found inside the 6.9 compared to the 6.3, and less evidence of hand- finishing (although the optional leather seats help), but neither car is in the Rolls-Royce class. Somehow the Germans have never been able to do wood convincingly.

Warmed up and on the move, both cars have contemptuously effortless acceleration, superb throttle response and, even in a world where 300bhp is routine in a big luxury car, these M100-engined Benzes still feel potent.

Warmed up and on the move, both have contemptuously effortless pace.

Both are low-revving overall, but develop huge torque at low speeds for that delectable feeling of power to burn. Yet where the 6.3 makes your neck-hairs tingle with giant lunges of Wagnerian thrust, the 6.9 delivers a sort of restrained excitement with the rough edges knocked off. It’s not really any slower, it is just more refined and makes less fuss about things.

In the earlier car, gearchanges are well defined because they are not smoothed by a torque converter. They aren’t rough, just very positive with four gears to the 6.9’s three. You can hold the 6.3 in the lower ratios by pushing the delight-fully spindly lever forward, whereas pulling the 6.9’s chunky plastic grip back through ‘D’ and ‘S’ into ‘Low’ feels more natural. Even under full throttle the 6.9 melds one gear into the next with a barely discernible flick of the rev counter and subdued thunder from beyond the bulkhead.

The 6.3 sounds fantastic but is understandably noisier in terms of wind as well as engine din. Not that the 450 is perfect: even in the late ’70s it was not regarded an outstandingly quiet car for its class in terms of either tyre- or wind-generated noise. What’s more surprising, and plays against type, is that the earlier car has the softer, more refined ride, demonstrating how good the air springs can be – when they work.

The power-assisted steering of these cars was perhaps the best to be found in any saloon of their respective eras. The 6.3’s helm feels only slightly woolly and uncertain after you have experienced the deft 2.6 turns between generous locks (for a 38ft turning circle) of the 6.9 which, like all W116s, had zero-offset geometry. Even the modestly talented could usually retain their dignity in this remarkably agile limousine.

Only a dedicated spotter will pick out the tiny badge and wider tyres that give away the iron fist beneath the W116’s velvet-glove exterior.

Not that the 300SEL has an especially tricky reputation for a 250bhp 1960s car with swing- axle rear suspension. You can corner it very fast, very safely in a state of gentle understeer and never take up too much road. The air springs self-level in all the right places and compensate for the fact that the 6.3-litre V8 is an immense lump of an engine. It was no accident that all of the M100-powered Mercedes cars needed a form of pressurised springing to compensate for the sheer heft concentrated in the nose, which would otherwise have meant an unacceptable compromise in favour of either handling or ride on conventional coil springs.

The 6.3 requires more of your attention than the 6.9 to drive quickly, but also feels a more specialist device than the later car – which is all part of its appeal, and in part the reason why prices of the few really good examples are firming up daily. Values are second only to Pagoda SLs and 280SE 3.5 Cabriolets in the hierarchy of perceived desirability, and some are now getting nut-and-bolt restorations that must absorb huge amounts of time and money. You can even get many of the bits new from Mercedes, but the prices would give most people heart failure.

Although the W116 Mercedes-Benz 450SEL 6.9 is probably the best (or at least the most practical) of all the M100 Benz saloons, it is easily the least appreciated. That said, the cult appeal that built up around the model after its tyre-shredding appearance in John Frankenheimer’s sparingly scripted and ambiguous post-Cold War thriller Ronin should not be underestimated.

Even so, it has yet to achieve the status that was predicted for it when production ended in 1980 because it is perceived as neither as obviously ‘classic’ as the 6.3 nor as conspicuously grand as the 600. As a consequence, it is not widely understood just how special and rare this car really is. If you merely want a large, grand, older-looking ‘chrome era’ Mercedes, there are many less financially ruinous ways of achieving this ambition than buying a 450SEL 6.9; the technical subtleties are lost on too many people who might anyway get frightened off by parts and servicing requirements that are less exacting than the earlier cars but still scary – especially if they relate to the engine (noisy timing chains, smoky top-ends, problems with the ECU) or the suspension system. These factors tend to depress the value of any 6.9 that looks anything less than pristine; fails to come with a service-history file the size of the Magna Carta; or cannot list a famous racing driver, a member of the royalty or God among its former keepers.

Other factors, however, look certain to secure the 450SEL 6.9 a place among the seriously collectable Mercedes of the near future. For a start, it will get rarer as a natural culling process sifts out the rusty, poorly maintained examples leaving only the shiny, well-brought-up cars to elevate the model’s image.

Secondly, it will move into the purchasing orbit of a generation of wealthy people coming into their 40s and 50s – who dreamt about owning the ultimate saloon of the 1970s when they were children. But couldn’t get any closer than a begged sales brochure, a game of Top Trumps or – if they were lucky – a rare glimpse of the real thing in town traffic or on a motorway fast lane: the well-recalled thrill of seeing the famous digits on right-hand side of the bootlid and the silky boom of dual exhausts.

Potent memories such as these will open minds and wallets, and make the 450SEL 6.9 the most hotly pursued Mercedes saloon of its generation – and a worthy alternative to a 6.3 if you can’t afford one. The 6.3 had enough acceleration to humble any Porsche 911 and most road Ferraris.

Clockwise: W116 feels a generation newer; vast V8 is up to 6.9 litres; optional leather adds to opulence; few saloons keep up with 6.9; auto has three speeds.