The Cosworth Connection -- How Mercedes-Benz Came to Boast a 16-valve Engine
Article by Graham Robson
Photos courtesy of Daimler AG Archives
When Cosworth was founded in 1958, it had one employee – Keith Duckworth – and operated from a rented garage in West London. Ten years later, based in Northampton, it was building world-beating Formula 1 engines. By the 1970s, Cosworth (the name is a contraction of the names of founding partners Mike Costin and Duckworth) was producing road-car engines with four valves per cylinder for Ford-UK and General Motors (Chevrolet, Opel, and Vauxhall), and it was then that Mercedes-Benz paid a call.
Even so, the engineers from Stuttgart were not received with open arms. For years, Cosworth had operated a “we really don’t want to expand any further” strategy, a game plan now in tatters. Cosworth welcomed companies asking it to design new engines, but it became increasingly difficult to convince Europe’s motor industry that Cosworth could not, or would not, then manufacture the engines in quantity. Building parts in batches of 100 was one thing, but there was no way that space could be found in Cosworth’s cramped assembly shops for more ambitious building to take place.
And, as Duckworth once told me: “Companies would come knocking on our door, saying, ‘We can’t get our engine to go. Will you have a look at it?’ But we didn’t want to give out our secrets without getting very well paid for it.”
Duckworth’s main secret: refining the basic engine layout of twin overhead camshafts, four valves per cylinder, and an efficient pent-roof combustion chamber into a neat, unbeatable, and potentially very powerful combination. Others had tried before him, but none had succeeded. For Mercedes-Benz, as for other clients, the attraction was that Cosworth remained independent – if the money was good and the timetable sensible, then the company was usually available.
After Ford-UK purchased the Cosworth-developed 16-valve BDA power unit (which went on to win thousands of races and rallies), General Motors knocked on the door, offering a major design job based on the light-alloy block of the Vega engine. Ford then asked Cosworth to design a “homologation special” for its Capri RS3100 race cars. Vauxhall wanted help to bail it out of trouble with the Chevette HS project, Opel wanted advice on the development of its 16-valve rally unit, and Mercedes-Benz was not far behind. By the 1980s, Cosworth actually had to turn work away.
In the meantime, Duckworth – and consequently Cosworth – was severely shaken after he suffered a heart attack in 1973 and was confined to a hospital bed for several weeks. It was this shock – Duckworth actually felt quite insulted by it – that caused a big sea change in the Cosworth organization in the mid-1970s.
“This was where I went out to find someone to assist me as a consultant,” Duckworth told me. “I ran into Alf Vickers at an Autocar ‘Thursday Club’ dinner at the Saxon Mill hotel, near Warwick. Alf had been managing director of Jensen for some years, and he’d just had a heart attack, too, and was away from his office, so you could say that we had a mutual interest.”
Vauxhall announced a new high-performance Chevette, the 2.3-liter 16-valve HS model, in November 1976, but needed to have the engine manufactured. Cosworth’s Ben Rood summarized the problem well: “Anyone can make two, and anyone can make a million. With two, you can do it by hand, and to do a million, you can afford to throw so much money at it that you can solve any problem. But between 500 and 10,000 of anything, that’s the most difficult production problem. I like to think that Cosworth is the best in that market.”
Cosworth did the Vauxhall job, which prompted an approach from Opel – and that, I think, is when Mercedes-Benz came to respect Cosworth. Opel had designed a 4-valve twin-cam conversion of its mass-production Ascona/Rekord unit, but it was not an immediate success. Engine designer Mike Hall, who had joined Cosworth from BRM, where he had designed the high-performance Lotus-Cortina engine, confirms:
“It was Manfred Tholl of PEK (Opel’s design/development center at Rüsselsheim) who dealt with us. What swung the decision was that Opel was also interested in productionizing the design after we had made modifications. All in all, Cosworth built between 1,000 and 1,200 production cylinder head assemblies.”
The real accolade, however, was still to come, as Duckworth told me:
“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-liter 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. They came to us because of our size and our capability. If they had just wanted a design, and the odd prototype, several other companies (like Porsche) could have done that.
“However, where Cosworth was totally unique was that it could start from a clean sheet of paper, design something, detail it, test and develop it, cast and forge the major items, then manufacture it in reasonable quantities. At the time, I don’t think there was any other business that could do this – certainly not in the UK, probably not at all in Europe.
“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.
“Their engine had a chain-driven camshaft, so we stuck with that, and for the first time I decided that we had to go for one-piece cylinder heads. The fact that we had by then the Cosworth foundry at Worcester, which could make much better complex castings than anyone else, helped enormously.”
Hall remembers:
“Our first target for the rally engine was 270 brake horsepower, in drivable ‘forest-stages’ trim. For tarmac use, or racing, we were looking for more than 300 brake horsepower. In both cases, we were to use Kugelfischer 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 fit together, then shipped it over to West Germany. I was asked to go there, we started it up on their dyno, ran it in, put it on power, and on the very first run it produced 267 brake horsepower. They were fairly impressed – and I was quite proud of that.
“By that time, we had so much experience that we could target an engine, specify it, and predict fairly accurately what we could produce. We built the parts for a few engines – about a dozen, if I remember correctly – and the idea was that we would eventually build a few hundred so that a car could be homologated.”
By this stage, though, Daimler-Benz had discovered that rally victories were hard to achieve, but it was determined to do just that. When the first approach to Cosworth was made in 1980, a costly (may I say ill-advised?) program was highlighted by failures, humiliations, and controversy. I described that program in my feature published in the November-December 2009 issue of The Star. In short, the cars then being used (450SLC/500SLC coupes) were far too heavy and unwieldy to be regular rally winners.
Then came a new strategy. Further-developed 500SLCs would have to be used in 1981, but they decided to develop a much smaller and nimbler sedan, hire the world’s fastest and most publicity-worthy drivers, and start work on a totally special, limited-production machine that would sport 4-wheel drive and be aimed at the 200-off Group B category. In both cases, a new twin-cam 16-valve engine would be needed – one that normally would be aspirated with fuel injection – and in due course, it was thought, turbocharging would be considered.
Competitions team boss Erich Waxenberger attacked this strategy with great energy. By telling them about the ongoing work at Cosworth, and by showing them drawings of a proposed Group B car, he managed to sign up Ari Vatanen from Ford and the German driver Walter Rohrl.
Then, suddenly, only two months later, at a press conference at the end of 1980, the company abruptly canceled its motorsport program. Rohrl (who had been on an exclusive deal) received a generous payoff, while Vatanen rejoined the Rothmans-Ford team. Both would go on to be World Rally Champions – their gain being Mercedes-Benz’s long-term loss.
All of Cosworth’s preparatory work seemed to be wasted, for the program teetered on the edge of cancellation. But not for long. Mercedes-Benz apparently had been impressed by the initial work completed by Cosworth and by the fact that the prototypes performed with very little trouble and produced competitive power (320 brake horsepower had been requested at the project stage, and there seemed to be every chance of achieving this in “tarmac/race” specification). Mercedes decided to proceed with a series-production version of the new power unit.
According to Hall, by then running the “road car” side of Cosworth’s engineering team:
“Instead of doing just 200 sets of racing bits, we were commissioned to make 5,000 production head assemblies every year. This meant that I had to modify the head to make assembly easier – and don’t forget that this was the first time we had ever had to think about making engines in such numbers, very large numbers by our standards. I’m sure Mercedes-Benz could have tackled the job themselves, but the numbers were really too low [by their standards], and in any case, the link with Cosworth gave them a certain amount of prestige.”
The result, unveiled in September 1983 but not entering production until 1984, was the Cosworth-designed road-car engine for a new car, based on the “small” W201 sedan and called the 190E 2.3-16. However, the bare bones of the engine, and the thinking behind the new sedan itself, were by no means as novel.
The M102 engine began as a new-generation 4-cylinder 1,997cc/2,299cc single overhead camshaft unit, first seen in 1979 (for 1980MY cars), while the W201 sedan was a totally new model that was on the shortest-wheelbase platform (104.9 inches) for a 4-door bodyshell since the original Ponton of 1953. Mercedes-Benz, for sure, planned a long life for both new building blocks.
For Cosworth, it was its first volume-production road-car engine contract, with heads cast at Worcester, machined at the new Wellingborough factory, and assembled by Cosworth into complete cylinder head assemblies before shipping them to West Germany. Cosworth, which had signed confidentiality agreements, expressed delight when the West German firm leaked the source of its new engines, and was always proud to be associated with them.
We did not know then that Mercedes-Benz had concluded that 4-valve layouts would eventually become widespread, and that the company intended to learn as much as possible from Cosworth’s engine before finalizing its own layouts, which would be produced in more impressive numbers in 4-cylinder, 6-cylinder, and even V-8 cylinder forms in the future. Cosworth, whose 4-valve layouts were not (and could not) be patented, was relatively relaxed about this, apparently viewing it as inevitable.
Before the new car was officially launched, Mercedes-Benz took prototypes to the Nardo high-speed test track (in the heel of Italy), setting 12 world long-distance endurance speed records at up to 151 mph. As launched in 1983, the production car was badged 190E 2.3-16 (a clear way to describe the engine layout) and boasted 185 brake horsepower (which, by Cosworth’s standards, was easily achieved). Compared with other W201 types, visual changes included redesigned front and rear aprons, a trunk lid transverse spoiler, and extra aerodynamic sills under the doors. In all respects, it was a civilized, well-finished, and reliable road car. Unhappily, it was only officially sold, in limited quantities, in the United States in 1986 and 1987.
It was quick by any standards. With a top speed of approximately 140 mph, and 0-60 mph acceleration in 7.4 seconds, it made the normal 130 brake horsepower 190E 2.3-liter car look pedestrian – which soon meant that original plans (to produce a mere 5,000 cars to secure Group A sporting homologation) were scrapped. Cosworth was put on full alert and asked to carry on producing 5,000 cylinder head assemblies every year.
Regular deliveries began in 1984, assembly was moved from Sindelfingen to Bremen in 1985, and production peaked at 8,656 in that same year. However, though the 2.3-16 eventually produced its full 320 brake horsepower, and more, for sedan racing, unless race regulations specifically banned turbocharged cars, it was always outpaced by Ford’s amazing 550 brake horsepower Sierra RS500 Cosworths.
With eligibility for racing in the German Touring Car Championship in mind, the 2.5-16 took over for the 2.3-16 at the end of 1988, the former car having a longer-stroke 204 brake horsepower/2,498cc version of the same engine. In March 1989, what became known as “Evo I” (specifically for use in motor racing) came along, which sported a big-bore/shortened-stroke high-revving 2,463cc derivative, with 201 brake horsepower on road cars but more than 350 brake horsepower in race-car tune. Bigger wheels, lowered suspension, flared wheel arches, and a bigger rear spoiler all helped to make it more suitable as a race car.
By 1990, the 2.5-16 was still selling at a rate of 1,270 cars per year, and there was a final flourish of the Evo 2, which was even more extreme than the Evo I. Although Cosworth continued to produce the special gas-flowed cylinder heads, AMG did some of the work for the racing versions of that car. This time around, too, there were more bodywork changes, larger wheels and tires, and a massive rear spoiler to help produce increased high downforce at high speeds.
Production petered out in 1992 – only 197 2.5-16s were built in the final year – but this project was certainly a major success, and image booster, for the three-pointed star. Not only were 26,128 Cosworth-influenced sedans built, but the 4-valve/twin-cam philosophy spread rapidly throughout the range.
One final thought: If 4-wheel drive had not swept through rallying in the early 1980s, could Mercedes-Benz have become worldwide rally winners in this period?
Production data and technical specifications for the 190E 2.3-16 can be found in The Star (March-April 2010, pp. 54-56), and at mbca.org.
