Four is Better
Four-Valve Engines at Mercedes-Benz
By Graham Robson
Images from Daimler Achives
Occasionally, just occasionally, Mercedes-Benz is not the pioneer of every new piece of high technology in automobiles. But, as far as I can see, neither has the company shaded its eyes and refused to acknowledge what the major rivals were doing. To a historian, it’s fascinating to look back, so as a backdrop to my story, I’ll just remind you that Mercedes was first in automotive use of diesel engines, gullwing doors, direct fuel injection, and the list goes on.
This story, though, is all about the use of engines with four valves per cylinder, for if you take the trouble to list every Mercedes-Benz car in the showrooms today, you will find that almost every single power unit – whether gasoline- or diesel-powered – has a twin-overhead camshaft, 4-valves-per-cylinder layout. The oddities that remain will assuredly be phased out in the near future.
Above, as originally engineered by the United Kingdom's Cosworth, this was the classic 4-valve cylinder head layout that would power so many Mercedes-Benz models form the mid 1980s.
Harking back to the late 1970s when the company decided that it should build a World Rally team, I followed the works team around South America on a monumental rally completely dominated by the new 450SLC 5.0 model. Yet this was an event won on strength, and reliability – and by spending a great deal of money – rather than with ultra-modern engines. Even then I did not realize that, behind closed doors, the company had concluded that it needed to do something to change that.
Racing has always been a test-bed and motivator for new technology. In 1914, Mercedes-Benz built this Grand Prix-winning race car, and it has survived for nearly a century. Shown alongside is the first of the Cosworth-engine 190E 2.3-16 sedans from 1984. Four-valve engines do not have to be bulky, as this shot of the engine bay makes clear.
Looking back, except for the use of supercharged engines in the 1920s (which was really an inspiration of Dr. Ferdinand Porsche in his relatively short tenure at Mercedes-Benz) and for the brave introduction of diesel engines in the 1930s, it was clear that the company was usually very conservative in its engine design processes.
Every thinking engineer already knew that the most efficient and practical way to get fuel/air mixture into and out of an engine was by using at least two inlet and two exhaust valves, each preferably operated by its own camshaft. But the cost and complication of providing new head castings and driving the two camshafts (four if a V-engine layout was considered) seemed to be prohibitive. For the moment, it seemed, it was better to produce rock-solid and strictly conventional engines, maybe larger and heavier than their rivals, than to attempt something technically advanced.
The magnificnet DB601 inverted V12 engine which powered several German military aircraft during WWII from 1939 to 1945, was a 4-valve unit that set many principles for future use.
Except for the design of aircraft engines in the 1930s – where, to be frank, the German government was footing the bills – this was not true of the passenger engines of that period. And I apologize for mentioning this yet again, but I have always been vastly impressed by the inverted V-12 DB600 family of engines that Mercedes-Benz designed to fit fighting machines such as the Messerschmitt Me109. Not only did these have overhead-camshaft cylinder heads and direct fuel injection, but they also had four valves in each cylinder.
Early postwar automobile engines had archaic side-valve layouts, and although the 300SL-type engine that followed was advanced in some ways, it was still a two-valve unit that could not sustain high rpm. Because its sales were prospering in the 1960s, the company was content with this situation – until BMW relaunched itself with new power units and became a real and viable rival. Mercedes’s immediate reaction was to produce the all-new, 2,746cc “six” – a fine engine with twin-overhead camshafts, but still with only two valves per cylinder. (In fairness, I should note that many other companies could be one-eyed when it came to spending money on new technology or by embracing the “It ain’t broke, don’t fix it” syndrome. Just think how long it took Detroit’s finest to accept unit-body construction, disc brakes, radial-ply tires and independent rear suspension).
In the meantime, what I call the “4-valve revolution” was sweeping over European motorsports – years after such layouts were adopted in North American racing. First there was Cosworth’s legendary DFV Formula 1 engine introduced in 1967, with Ferrari and BRM soon following; rally teams as diverse as Ford, BMW, Fiat and Lancia soon joined in. Even so, it was not until Mercedes-Benz set out on a full-scale rally car program in 1979 that it realized change would be needed.
Before the company adopted 4-valve technology, Mercedes Benz adopted twin overhead camshaft valve gear – this being the M110 2,746cc “six” of the 1970s.
At this point, I beg indulgence to re-quote a sequence I detailed when writing about works rally cars from Stuttgart. Having recently saved GM’s Opel subsidiary from trouble with that company’s 16-valve project, Cosworth learned of another approach in engine design. Quoting Cosworth’s founder, Keith Duckworth: “The next breakthrough came in 1980. It was Mercedes-Benz, straight out of the blue. They wanted us to design a 4-valve rally engine based on the bottom end of their new 2.3-litre M102 single-cam 4-cylinder unit. They had already done their own 4-valve twin-cam design, but were happy to admit that it wasn’t good enough.
“Mercedes-Benz gave us a completely free hand – they were super people to work with, and to get such a contract from them, it was almost like getting the Royal Warrant. Although we had to use their cylinder block, they wanted a no-holds-barred race/competition engine for a special Mercedes-Benz model.
Starting with the R129-type of SL sports car of 1989, the company launched a completely re-engineered 4-valve twin-cam evolution of the well-established 5.0-liter V-8 engine.
“Our first target for the rally engine was 270 horsepower, in driveable “forest-stages” trim. For tarmac use, or racing, we were looking for more than 300 horsepower. In both cases, we were to use Kugelfischer fuel injection. We didn’t ever run one of those engines at Northampton. Two technicians came over from Stuttgart, and between us we built up an engine to make sure that all the parts fitted together, then shipped it over to West Germany. We started it up on their dyno, ran it in, put it on power, and on the very first run it produced 267 horsepower.”
Mercedes-Benz was apparently so impressed by the initial work, and by the fact that the prototypes performed with very little trouble and produced competitive power (320 horsepower had been requested at the project stage, and there seemed to be every chance of achieving this in tarmac/race specification), that the decision was made to go ahead with a series-production version of the new power unit.
Instead of producing just 200 sets of racing bits, Cosworth was then commissioned to make 5,000 production head assemblies every year. The result, unveiled in September 1983 but not entering production until 1984, was the Cosworth-designed road-car engine for a new model, based on the compact W201 sedan and called the 190E 2.3-16 model.
This is the classic single overhead-cam 2-valves-per cylinder 3.0-liter engine of the 1980s ...
and this is the thoroughly updated 1989 derivative of it, complete with four valves per cylinder and twin-overhead camshafts
Even while development of this new engine was moving forward, the decision was made to go 4-valve with many of the company’s future power units. Other European companies – BMW and Porsche among them (Mercedes-Benz kept a very close eye on its home-country competitors) – were on the same path, and the company was not about to fall behind, neither in the technical- nor in the engineering-trends stakes.
It was typical of Mercedes-Benz, however, that neither was accomplished in haste without thinking deeply about all the possible consequences or giving thought to capital costs. Gone were the days when one engine design might be used in two or perhaps three different models with an aim to be retired after only a decade or so. Big bucks were now involved – hundreds of thousands of power units would probably be built, and every car/model/transmission/engine bay combination would need to be considered. Personalities in the industry have often said to me that Cosworth’s biggest attraction as consultants was that they paid so much attention to detail, in a manner similar to the way that Mercedes-Benz started out on its own developments.
Action behind the scenes was frenetic for a time, but it was a real surprise to find that when the new-generation R129 SL-type was unveiled in February 1989, it featured not one, but two new types of 4-valve twin-cam engines. First of all, there was the new 300SL-24 “six,” which had a 231-horsepower, 2,960cc engine, this then being topped by the latest 500SL, which had a 326-horsepower, 4,973cc V-8.
These engines were much more powerful and efficient than the engines they replaced. To quote my good friends at Britain’s Autocar magazine at the time: “The frenetic activity ... has resulted in a new range of multi-valve engines that crush any weight penalty. Indeed, the new 300SL-24 outperforms the old 420SL, and the DOHC 5-litre V-8 is quicker than the old 560SL. ...”
Although a totally new V-12 had not yet been revealed, the editors’ comments were instructive: “The 400-horsepower V-12 will surely be quick enough to monster anything from [BMW] Munich and that’s certainly Stuttgart’s intention. But Bruno Sacco, head of Mercedes’s design team, with his thoughts clearly on the creation of a superior image, says: ‘If it was up to me, we would have developed a V-16.’
“Over the next couple of years, multi-valve engines will become the norm across the entire Mercedes-Benz range.”
Once it decided to produce all automotive engines as 4-valve twin-cam units, progress at Mercedes-Benz was swift. This was the massive and impressive 6.0-liter V-12 engine as launched for the 600SEL in the early 1990s.
Both these new 4-valve units were no-holds-barred updates of existing 2-valve, single-cam engines, of course, but the heads included the very latest technology in that the timing of the inlet camshafts was variable over a wide range, using a combination of hydraulics and electronics to cut pollutants and fuel consumed at all speeds.
This, in fact, was just a start to the avalanche of new multi-valve engines that Stuttgart would announce in the early 1990s. First of all, there was a totally new generation of small 4- and 6-cylinder engines that were fitted to the best-selling W124 range from 1992, and for 1994, there was even a really brave marketing breakthrough – the addition of 4-valve diesel engines for cars in the new C-Class series, and soon for cars in what became known as the E-Class. When you add the big improvements that were then made by the near-universal adoption of exhaust-driven turbochargers and by common-rail diesel fuel injection, it is easy to see why diesel-engine cars gradually took over in Europe, even though North American customers do not yet seem to be convinced.
By the end of the century, therefore, the technological and marketing battle was truly over, and it would now be unthinkable to see a new engine produced with fewer than four valves per cylinder. Or is there something going on behind the scenes in Stuttgart that will amaze us all in the coming decades?
Who Was First with Four
Amazingly, Mercedes-Benz was not first on this occasion. Most historians now agree that the pioneer was Fiat with the S61 Corsa of 1908, a monster with a 115-brake horsepower 11-liter engine, which raced mainly in the United States. No doubt inspired by this and the Peugeot Grand Prix engine of 1912, the first 4-valve Mercedes-Benz engine was the one-race, one-victory French GP winner of 1914 before a series of successful military aircraft engines that it subsequently inspired followed during the war from 1914 to 1918. The rest is history. The world’s first 4-valve production road car, incidentally, was the British Bentley 3-liter of 1921 – mere hundreds were manufactured, not thousands.
If Four, Why Not Five
No, don’t laugh. Five-valve engines have been tried, and even sold in big numbers (think Audi in the last 20 years, and some Ferrari road cars, for instance), but most people agree that the economic limits for such units have passed. Five valves usually means three camshafts and complex drive arrangements. Oh, and by the way, there is little evidence that they produce better power or torque than carefully developed 4-valvers.
Then and Now
Mercedes-Benz Engines in 1978 and 2012
Purely for interest, this lists the families of engines used on Mercedes-Benz private cars in 1978 (immediately before the Cosworth connection was forged) and 2012 :
1978 2012
Gas, 4-cyl, 1,988cc/2,307cc, Gas, 4-cyl, 1,595cc, 2OHC, 4-valve
OHC, 2-valve
Gas, 6-cyl, 2,525cc, OHC, 2-valve Gas, 4-cyl, 1,796cc, 2OHC, 4-valve
Gas, 6-cyl, 2,746cc, 2OHC, 2-valve Gas, V-6, 3,498cc/2,996cc,
dual OHC, 4-valve
Gas, V-8, 3,499cc/4,520cc/5,025cc, Gas, V-8, 4,663cc,
OHC, 2-valve dual OHC, 4-valve
Gas, V-8, 5,439cc, OHC, 3-valve Gas, V-8, 5,461cc, 2OHC, 4-valve
Gas, V-8, 6,332cc/6,834cc, Gas, V-8, 6,208cc, 2OHC, 4-valve
OHC, 2-valve
Gas, V-12, 5,461cc/5,513cc/ 5,980cc,
OHC , 3-valve
Diesel, 4-cyl, 1,988cc/2,197cc/2,404cc, Diesel, 4-cyl, 1,796cc/2,143cc,
OHC, 2-valve dual OHC, 4-valve
Diesel, 5-cyl, 2,998cc/3,005cc, Diesel, V-6, 2,987cc, 2OHC, 4-valve
OHC, 2-valve
Today the list of engines could conceivably have been even more, of course, except that the company’s product planners have been ruthless in applying what I call the “building block” technique to the range. Maybe it isn’t obvious in cars sold in the United States today, but it is astonishing to see just how many different Mercedes-Benz models now use the 1,796cc gasoline engine, or the V-6 2,987cc diesel engine.