Mercedes-Benz V8
by F. Wilson McComb

CHAPTER 5 - 6.9 Litres

A sad side-effect of the New S Class's arrival in 1972 was that it killed off the 300 SEL bodyshell, and with it Europe's favourite motorway cruiser, the 300SEL 6.3. At the time it was still selling steadily, and some owners were anxious to buy another, the earliest examples being then three years old. Daimler-Benz assured them a replacement was on the way. Neither they nor anyone else knew that this 135 mph limousine would have no successor for a further three years, at least.

The formula seems simple enough: take the best bodyshell in your current range, cram the largest available engine into it, and there you are. However, Stuttgart's methods were no longer as crudely direct as that. In this case they were very keen to refine the basic concept a great deal, and some of those refinements had to keep step with developments elsewhere in the model range. Then there was the fuel crisis of late 1973, making it a tactless time to announce a large car with the kind of performnance that causes any self-respecting conservationist to go purple with righteous indignation. So although the new 450 SEL 6.9 Mercedes-Benz could have been released at the 1974 Geneva Show, if not sooner, they decided to hold it back for another year. Even then, it was to be a low-profile exercise because there was a waiting-list of several hundred who wanted the car now, whatever its specification might be. Shown to the European press in May 1975, the new model was still unobtainable in Britain or America until late 1976.

 

Suspension For the 450 SEL 6.9-litre of 1975, the Series 116 suspension layout was combined with a highly sophisticated system of nitrogen-filled pressure reservoirs and oil-filled struts with gas-filled dampers. As before, it was self-levelling and adjustable for ride firmness and height while on the move.
Suspension
Self-levelling system
The engine was of course the 6.3-litre V8, but modifžed and developed until little other than the 95 mm piston stroke remained. Bored out to 107 mm, it became even more oversquare than before and the capacity was increased to 6834 cc. It had the K-Jetronic injection and ingenious hydraulic-fulcrum rocker arms that were also being adopted for the smaller-capacity V8 engines, plus fully transistorized contactless ignition and a new type of head gasket by Reinz-Repa (generally but incorrectly called Ferrolastic) which made periodic tightening-down unnecessary. A change to dry-sump lubrication made it easier to fit the engine into the Series 116 bodyshell, and almost doubled the total oil capacity. With these modifications, said Daimler-Benz, the engine could be virtually left to its own devices for the first 50,000 miles of its life. Maximum power output was 286 bhp at 4250 rpm, and maximum torque 405 lb ft at 3000 rpm, representing improvements of almost 15 and 10 per cent respectively over the 6.3-litre engine's performance, and at just a few hundred rpm more.

under the hood Based on the 6.3-litre engine of the Grosser Mercedes, the new 6.9-litre V8 gave fifteen per cent more power, and Stuttgart's many detail improvements made the unit maintenance-free for its first 50,000 miles.

on the track
Extensive testing and development work ensured unrivalled stability at high speed in the new 450 SEL 6.9-litre, which was arguably the world's finest motorway cruiser.

But high performance, Professor Dr Hans Scherenberg insisted, was merely a by-product of the Company's search for greater all-round driving comfort. The increased engine output was partly to compensate for increased weight, and part of that was accounted for by something special. Far out of sight under the now-familiar 450 SEL hodyshell was a new suspension system that Daimler-Benz referred to as 'hydro-pneumatic', though some such term as 'oleo-gas' might have been nearer the mark. Like most things emanating from Stuttgart, it was the result of continual development work - and although nobody cared to mention the fact, it also solved a serious problem. The self-levelling air suspension eventually standardized on the 300 SEL had had a distressing habit of giving way somewhere, when the car was stationary, if the balancing valves became faulty. The car would cheerfully sit up again as soon as the engine started, of course, but no Mercedes owner enjoyed finding his pride and joy collapsed in a corner like a sick camel. The S Class cars had reverted to steel springs for the semi-trailing-arm suspension of Series 116 models, with (later on) the option of an engine-driven self-levelling device at the rear.

This was now further developed for the 6.9-litre version of the 450SEL by eliminating the steel springs again, front and rear, and combining the otherwise standard Series 116 suspension with a highly sophisticated arrangement of nitrogen-filled pressure reservoirs and oil-filled struts, the latter incorporating gas-filled dampers. It was self-levelling, it provided full spring travel at all times, and the ride height could be adjusted on the move, either to compensate for a heavy load on board or to increase the ground clearance when required. The effect was to combine all the tautness and stability of S Class suspension (including its anti-dive and anti-squat controls) with the additional comfort of fluid suspension, while eliminating the pitch and wallow of Citröen's somewhat similar system.

Dry sump / rocker arm
Dry-sump lubrication reduced engine height to get the 6.9-litre tucked under the 450 SEL bonnet, and new refinements included an ingenius hydraulic-fulcrum rocker arm, later adopted for the smaller V8 engines and still used on the lateset 3.8 and 5.0-litre models

Daimler-Benz claimed a maximum of 140 mph for the new saloon (though some testers put it much closer to 150 mph) with 0-60 mph acceleration in under 7.4 seconds. To put it another way, this meant they had produced a four-seater luxury limousine with the performance of the contemporary Maserati Khamsin or V12 Jaguar E type. At the time of the press review, the tax-paid German price was said to be about DM65,000, then the equivalent of $28,000 or £12,000. The ordinary 450SEL was then selling for almost £11,000 in Britain, and the cheapest Rolls-Royce cost nearly £15,000. However, when the 450SEL 6.9 eventually reached the UK in late 1976, the price had somehow climbed to £22,000, and Rolls-Royce were selling their Silver Shadow II at £28,600. In early 1979 the gap was even wider -- £28,600 for the Mercedes and £32,000 for the Rolls -- but by the end of the same year the German car had a £30,500 price tag to a staggering £36,650 for the British one. The two were no longer even in the same price-bracket.

The 260 km/h (162 mph) speedometer of the 450 SEL 6.9 did not flatter too wildly. Although only 140 mph was claimed by Mercedes, Motor saw a two-way mean 144, and Paul Frère drove another example at 148 mph. For a full-sized luxury saloon, that's quick. behind the wheel

At first acquaintance with the car, Autocar said, "The quality of the Stuttgart development engineers, all keen drivers and with authority to back it up, shows through at every corner ... It is only the driver who can appreciate why this car costs so much." Road & Track, though based less than forty miles from Hollywood, ran right out of new superlatives and called it "The fastest, best sedan in the world." A little later, Motor (who had been very lukewarm about the ordinary 450SEL a couple of years earlier) went wild about the 6.9-litre after a fuller test: "Exclusive, fast, immensely safe and beautifully made ... Without doubt the greatest Mercedes yet ... A first-class showcase of outstanding technological achievements." But Autocar, later still, swung the opposite way to compare the Mercedes unfavourably with the cheaper (in England) Aston Martin V8 and the very much cheaper Jaguar XJ 5.3. They omitted to mention that the Silver Shadow II (then costing £3400 more than the Mercedes) took nearly twice as long to achieve three figures, had a top speed at least 25 mph lower, used appreciably more petrol and was arguably less comfortable than its German equivalent.

Some people find it diffžcult, even impossible, to understand the appeal of the 450SEL 6.9. Here was a car that looked exactly the same as another Mercedes costing £11,000 less in Britain at the time of writing. Only the fatter tyres and a little '6.9' badge on the tail gave the game away (and you could, if you wished, have the badge left off). On the road, this superlative vehicle could even be mistaken for one of the still smaller models at perhaps a third of its price. It was therefore poles apart from the Wagnerian splendour of the model 600 Pullman, or the flamboyance of the pre-war Grosser Mercedes. In terms of subtlety, you might as well compare a performance by Sir Alec Guinness with a turn by Danny La Rue.

rear 3/4
More costly than the ordinary 450 SEL by more than £11,000, the 6.9-litre could only be recognized by its fatter tyres and '6.9' badge on the boot-lid. The very rich and modest could even have the badge omitted.

It follows, then, that if one's car is intended primarily to be a status symbol proclaiming one's opulence to all, this last of the big-engined Mercedes-Benz was much too unobtrusive to serve. For that, the popular choice runs to a taller radiator shell sumounted by a different mascot. Cars are, like clothes, a matter of personal taste, and not everybody who can afford a Pucci shirt will wear it with the label hanging out. Some enjoy the blatant swagger of a blood-red supercar that makes every head turn-including, alas, those in peaked uniform caps with a checkered band around them. Others prefer something very unpretentious-looking, in which it is possible to travel at a consistently higher speed without attracting any attention whatsoever.

The 6.9-litre Mercedes was built in a country without overall speed limits, where cars are still driven fast over considerable distances, and designed by men who know exactly what a driver needs in order to motor safely and fast for long periods at a stretch, solo or in company, with absolute confždence and comfort. Besides the usual conveniences of a luxury saloon -- electric window-lifts, centralized door-locking, air conditioning, headlamp wash/wipe, etc. -- there are less obvious features like ingeniously ribbed rear lights that remain clean in wet weather, heat-absorbing glass all round, a laminated windscreen and rear window, head-rests and safety belts for all passengers, automatic transmission with cruise control, and a ZF limited-slip differential.

The seats are quite firm -- too firm, some testers insisted -- but a long journey proves they offer support in the right places. The steering wheel is slightly larger than modern fashion dictates, because Daimler-Benz have studied this, as they have studied everything else, and believe that a large wheel encourages a more relaxed, less aggressive style of driving. The instruments, too, sacrifice nothing to the whimsies of some styling department: a large, circular 160 mph speedometer dead in front of the driver is flanked by a tachometer (redlined at 5250 rpm) and a cluster of fuel gauge, oil pressure gauge and coolant thermometer. Like all the controls, the gear selector is perfectly placed and works with a precision that is sheer joy.

Forward visibility is excellent, and as usual the big three-pointed star serves as a convenient sight for aiming this projectile. As one accelerates to a three-figure cruising speed (in twenty seconds or less) one can not only feel oneself being thrust back into the seat, but also hear a subdued snarl from the engine and transmission. lf this annoys you, the Mercedes is not your sort of car -- but how can it be irritating to hear beautifully assembled machinery doing its job so willingly? And telling you somehow that you may rely on it to continue doing so indefinitely, for the message it conveys is that Daimler-Benz inspectors disapprove of Freitag cars.

Again, although the suspension system is one of the most sophisticated ever designed, it will give audible warning of a major change in road surface, and this may either please or infuriate you, depending on the amount of cotton wool you want to have around you in a fast car. This is one of the roomiest cars there is, having more legroom and interior width than a Rolls or a Cadillac, yet it can be chucked about like a good sports car- which means it can be parked or manoeuvered in heavy traffle with equal ease. With probably the best power-assisted steering and brakes in the world, it is totally under the driver's control at all times, and does without effort exactly what it is told to do. To these virtues, one other must be added. Besides being amazingly stable at high speed, either when cornering or when running straight, the 6.9-litre also feels stable, which is not the same thing at all. Some people place more value on this than others do, and I am emphatically one of them.

6.9 at Nice
The 450 SEL 6.9 is pictured at Nice, where the first Mercedes cars showed their paces eighty years ago, Werner winning the Nice race by half-an-hour on 25 March 1901 and La Turbie hillclimb four days later

At one time, Stuttgart planned to update the model 600 to bring it more in line with 450 SEL 6.9 specification, but it would have involved more work than Grosser sales justified. So the 6.3-litre model 600, which is still available (at a price), is in many ways an old-fashioned car compared to the 6.9-litre, which has now reached the end of its production life. In years to come we may look back on the 6.9 as being -- within its own genre -- the ultimate expression of automotive design.



Reprinted from Mercedes-Benz V8, by F. Wilson McComb
Editor: Osprey Auto History 1980

materials provided by:
Giovanni Verzoletto