The Power of Eight
The M100
The First production V-8 in Mercedes History

by Graham Robson
Images from Daimler Archives

Yes, improbable as it might seem, the very first production car V-8 engine from Mercedes-Benz wasn’t produced until 1963. Although the company and its constituents had already been in business for nearly 80 years, no previous private car had ever been sold with a V-8 engine. In the 1930s, of course, the Grosser models used a straight eight, the legendary W125 GP cars were straight eights, in 1939 the 1 1/2-liter W165 race cars used V-8 engines, and in the 1950s the W196 and 300SLR types both used straight eights – but no V-8 had ever been installed on a Mercedes-Benz road car.
The big change – the first in a whole series of big changes – then followed at the end of the 1950s. Although Mercedes-Benz was still expanding rapidly, it had not developed a new flagship engine for a decade, for the M186 (as described in Parts 1 and 2 of this series) was still in use. Ideas – but they were apparently no more than ideas – had  started to circulate in the late 1950s, but in postwar Germany there was no real encouragement to turn those ideas into an actual design.
Cadillac, of course, had been building modern overhead-valve V-8s since 1949, and by 1959 these had evolved into 6.4 liters/390 CID engines, with 345 horsepower (SAE). However, the real impetus – and I insist that this was a major influence – came at the end of 1959 when Britain’s Rolls-Royce, that most traditional of all brands, suddenly launched its own all-new V-8 engine (much influenced, it’s been said by Chrysler and Cadillac’s latest offerings.…) – a 200-horsepower, 6.25-liter unit – and for the first time, Mercedes-Benz looked as if it would be out-gunned, especially in certain prestigious export markets.
It was at this time that the technical team was given freedom to develop a successor to the old-type M186/M189. Not only was a brand-new top-of-the-range engine needed, but it had to be the best – better, with more potential, than anything that Mercedes-Benz had yet to face in the marketplace. In particular, it had to be an ideal power plant to power a massive new sedan, the W100, which we would come to know so affectionately as the “New Grosser,” or the 600. Now, more than at any previous time, the company wanted to provide a peerless new top-of-the-market model, one that would appeal to royalty, heads of state, and business tycoons all over the world.
So, where to begin? Because the new 600 was likely to weigh at least 5,500 pounds (6,000 pounds for the projected longer-wheelbase “Pullman” version), updating the dear old 6-cylinder M189 type, which had reached its limits, was out of the question. It looked as if at least 250 horsepower (net) – a figure often quoted in North America as 300 horsepower SAE – would be needed, along with at least 350-370 pound-feet of torque: This was quite out of reach for the old M189 type. With the new engine, it was forecast that a new 600 model would be able to reach 130 mph, and you may be sure that no one even worried about the awful fuel economy that would accompany this.
Given a free hand, the design team therefore sat down to think .... then thought some more. As many engineers would agree – particularly those swept along by the current passion for modern V-8s in Detroit – such torque could only be produced by providing a big increase in piston area, and this, almost by definition, meant that at least eight cylinders would be needed, but not more than eight.
No one in Stuttgart seriously considered going for a V-12 – Ferrari was the only company currently building V-12s in any numbers, and no one built them in quantity – and a straight eight would have been too heavy and too bulky, so what the Detroit-lovers would consider as the go-to solution – a V-8 layout – virtually chose itself.
As most Detroit-watchers already knew, a modern V-8 offered a very compact, easy-to-install, package for a new automobile. V-8s tended to be virtually cubic and shorter than the equivalent-displacement straight six, so because the style of modern cars was already providing very wide engine bays, this was an ideal configuration.
The design and layout then, effectively, started with the target power and torque figures, and worked backward to the details needed to achieve those figures. The need for stump-pulling torque, and the ability to work with automatic transmission, dictated the basic bore/stroke layout, which ended up at a bore of 103mm/4.06 inches, a stroke of 95mm/3.74 inches and a swept volume of 6,332 cc/386 CID.
To an American enthusiast, already used to seeing such figures on big Detroit-mobiles, there would be nothing outstanding about this – yet here was the largest-capacity automobile engine that Mercedes-Benz had produced since the last 1939-type 770 Grosser had been built. It was to be a massive, modern, and technically advanced power unit that would set new standards in Stuttgart for many years to come. It had to be, of course, because it was estimated that to drive all the auxiliaries involved in this huge new car – which included powering complex hydraulic circuits to operate the air suspension, the power windows, power seats, air conditioning, and dual electrical alternators – at least 50 horsepower was needed on board before the balance of the power output could reach the rear wheels! .
With the basic layout settled, much of the rest of the remaining specifications seemed to write themselves. Once the team had decided that it was not yet sufficiently confident in producing light-alloy cylinder blocks, the engine grew up around a conventional cast-iron block, complete with five main crankshaft bearings, while the cylinder heads themselves were aluminum alloy. This, incidentally, meant that the engine assembly itself, complete with all add-ons and auxiliaries, would be very heavy – no less than 750 pounds.
The layout of the cylinder heads was a logical evolution of the layout refined over the years on the earlier M189, though that car’s interesting slant-face joint with the cylinder block had been abandoned, and what we might call conventional wedge-profile combustion chambers were adopted.
The castings embraced chain-driven single-overhead-camshaft valve gear, where sturdy fingers were interposed between the camshaft lobes themselves and the valve stems; to keep the overall width of the engine within bounds, this line of fingers was now positioned in-bound on each cylinder head. Lining up with the same width-saving theme, the valves were also canted over toward the engine center line too.
The Bosch fuel injection installation, with timed impulses provided by an 8-cylinder pump mounted neatly in the center of the vee, had its nozzles fixed into the inlet manifolds and pointing directly downstream at stems of the inlet valves, rather than in the cylinder heads themselves, and it was a visual feature of this enormous (by European standards) engine that the inlet manifolding featured two fore-and-aft “logs” mounted above the engine, aligned with the camshaft covers themselves.
It was really only a company as accomplished as Mercedes-Benz that was able to produce such a complex, powerful and (by definition) expensive-to-build new power unit. Because the 600 was always going to be an expensive low-volume car – at peak, no more than 408 cars were sold in a complete year – massive investment in engine machining and assembly fixtures was neither needed, nor ever installed.
Left on its own, this wonderful engine might even have been written off by historians as a time- and money-wasting indulgence – except that due to development chief Erich Waxenberger’s single-handed determination, it somehow was shoe-horned into the body shell of the W109 300SEL saloon, the result being the 300SEL 6.3 of 1968-1972. It tells us everything about the size of the W109’s engine bay that this monstrous power unit could be installed with few changes (and no diminution of the power output), and that the overall balance of that car’s chassis was not destroyed.
Waxenberger himself would win a six-hour touring-car race in a 300SEL 6.3 at the Portuguese enclave of Macao, near Hong Kong, though a similar entry at the Belgian Spa race was abandoned because of tire problems. Thereafter, his racing ambitions for this car were thwarted. At the time, incidentally, a German magazine published a cartoon of Waxenberger trying desperately to insert a WWII-type DB601 V-12 aircraft engine into the same type of car, the caption stating: “It’s got to go in, it’s got to go in ....”
Depending on who applied them and how the development overhead costs were applied, the 300SEL 6.3 of 1968-1972 was probably profitable to the company, for 6,526 cars were built, though the peak year was 1969, when 2,578 were built.
The company, however, was happy to try again, for once the new generation W116 S-Class had established itself in the 1970s, a 450SEL 6.9-liter car appeared, and no fewer than 7,380 of those machines found customers, nearly 2,000 of them in 1977 and again in 1979.
The model name gives us a clue as to what changes were made, because the engine’s cylinder bore was increased slightly, to 107mm, the swept volume therefore rising to 6,834cc, and (to maintain a low engine height) a dry-sump engine installation was chosen. Not only that, but this became the first passenger car engine from Stuttgart to use Bosch’s latest K-Jetronic fuel-injection installation. (See also pages 54-57.)
This was a very fast car by any standards, for in the 1970s, a top speed of 140 mph, with 0-100 mph acceleration in no more than 19.5 seconds was “super-car” stuff – even if one had to work hard to get better than 12 mpg fuel mileage. Not that many rich drivers cared too much about fuel mileage in those days – not, that is, until what became known as the “second energy crisis” erupted, the Shah left town, and the atmosphere for fast motoring changed completely.
All this, of course, was before AMG came on to the scene – but that is a story for another day.…


V-8 Engine Development
1930s    Fuel injection first used on Mercedes-Benz diesel-engined cars.
1963    M100 V-8 engine with 6,332cc/386CID first revealed in new 600 model.
1968    Announcement of 300SEL 6.3 (M100) engine squeezed into W109 300SEL body.
1972    Final production of 300SEL 6.3 model –
6,526 cars built.
1975    Launch of 450SEL 6.9 – up-dated M100 engine squeezed into W116 450SEL body.
1980    Final production of 450 SEL 6.9 model –
7,380 cars built.
1981    Final 600 derivative produced.
Total production: 2,677 cars.
Total production of M100-engined models 16,583

Baby Brother
We must never confuse the magnificent M100 V-8 with the smaller M116 V-8 that followed, and which first appeared in 1969. Although the two power units looked very similar – both were single-overhead-camshaft V-8s with Bosch fuel injection – they were different in every detail. Mercedes-Benz, indeed, assured us that not one single component or casting was shared between the two designs.
  For comparison
Original M100    103mm bore x 95mm stroke        6,332cc
Original M116    92mm bore x 65.8 mm stroke        3,499cc
Although the layout of the two engine families was broadly similar, there were many detail differences. The architecture and water cooling systems of the heads were different, and the injector nozzles on the smaller engine were in the head castings, rather than in the inlet manifolds, while the “fingers” between the camshafts and the valve stems themselves were outboard on the small engine, and inboard on the M100 type.
Not only that, but the spacing between cylinder bores was much more generous than expected, this suggesting that the planners already had much-enlarged (over-bored and longer stroke) derivatives in mind for future models. By the end of the 1970s, 5.0-liter versions were already available – and further enlargement was to follow.

Opposite page: The M100, the first production V-8 in Mercedes-Benz history. Above: A cutaway view of the 600. Below: The first version of the W100 luxury sedan, the “New Grosser” 600 SWB (short wheelbase), introduced in 1963.  

Left, from top: The air intakes feeding the fuel injection between the cylinder banks. Cutaway illustrates the 8-cylinder Bosch fuel injection system feeding into the parallel intake manifolds.  Auxiliary systems mounted on the sides. The last M100 engine in 1977-79 as installed in the W116 450SEL 6.9 Right: The New Grosser 600 long-wheelbase (LWB) 4-door Pullman, with all its accessories, needed the torque of the big engine.