Sierra Cosworth - Development

The Ford Sierra RS Cosworth is a high-performance version of the Ford Sierra that was built by Ford Europe from 1986 to 1992. It was the result of a Ford Motorsport project with the purpose of producing an outright winner for Group A racing in Europe.

The project was defined by Stuart Turner in the spring of 1983. He had recently been appointed the head of Ford Motorsport in Europe, and he realised right away that Ford was no longer competitive in this area.
Turner got in touch with Walter Hayes, at the time the vice-president of public relations at Ford, to get support for the project. Hayes had earlier been the driving force behind the development of the Ford GT40 that won Le Mans in 1966, and the Cosworth DFV engine that brought Ford 154 victories and 12 world championships in Formula One during the 1960s and 1970s. Hayes found the project very appealing and promised his full support.
Turner then invited Ken Kohrs, vice-president of development, to visit Ford’s longtime partner, the automotive company Cosworth, where they were presented a project developed on Cosworth’s own initiative, the YAA engine. This was a twin cam, 16-valve engine based on Ford’s own T88 engine block, better known as the Pinto. This prototype proved an almost ideal basis for the engine Turner needed to power his Group A winner.
Therefore, an official request for a turbocharged version (designated Cosworth YBB) capable of 180 HP on the street and 300 HP in race trim, was placed. Cosworth answered positively, but they put up two conditions: the engine would produce not less than 150 kW (204 HP) in the street version, and Ford had to accept no fewer than 15,000 engines. Turner’s project would only need about 5,000 engines, but Ford nevertheless accepted the conditions. The extra 10,000 engines would later become one of the reasons Ford also chose to develop a four-door, second generation Sierra RS Cosworth.
To find a suitable gearbox proved more challenging. The Borg-Warner T5, also used in the Ford Mustang, was chosen, but the higher revving nature of the Sierra caused some problems. Eventually, Borg-Warner had to set up a dedicated production line for the gearboxes to be used in the Sierra RS Cosworth.
Many of the suspension differences between the standard Sierra and the Cosworth attributed their development to what was learned from racing the turbocharged Jack Roush IMSA Merkur XR4Ti in America and Andy Rouse's successful campaign of the 1985 British Saloon Car Championship. Much of Ford's external documentation for customer race preparation indicated "developed for the XR4Ti" when describing parts that were Sierra Cosworth specific. Roush's suspension and aerodynamics engineering for the IMSA cars were excellent feedback for Ford. Some production parts from the XR4Ti made their way into the Cosworth such as the speedometer with integral boost gauge and the Motorsport 909 chassis stiffening plates.
In April 1983, Turner’s team decided on the Sierra as a basis for their project. The Sierra filled the requirements for rear wheel drive and decent aerodynamic drag. A racing version could also help to improve the unfortunate, and somewhat undeserved, reputation that Sierra had earned since the introduction in 1982.
Lothar Pinske, responsible for the car’s bodywork, demanded carte blanche when it came to the appearance to make the car stable at high speed. Experience had shown that the Sierra hatchback body generated significant aerodynamic lift even at relatively moderate speed.
After extensive wind tunnel testing and test runs at the Nardò circuit in Italy, a prototype was presented to the project management. This was based on an XR4i body with provisional body modifications in fibreglass and aluminium. The car’s appearance raised little enthusiasm. The large rear wing caused particular reluctance. Pinske insisted however that the modifications were necessary to make the project successful. The rear wing was essential to retain ground contact at 300 km/h, the opening between the headlights was needed to feed air to the intercooler, and the wheel arch extensions had to be there to house wheels 10” wide on the racing version. Eventually, the Ford designers agreed to try to make a production version based on the prototype.
In 1984, Walter Hayes paid visits to many European Ford dealers in order to survey the sales potential for the Sierra RS Cosworth. A requirement for participation in Group A was that 5,000 cars were built and sold. The feedback was not encouraging. The dealers estimated they could sell approximately 1,500 cars.
Hayes did not give up, however, and continued his passionate internal marketing of the project. As prototypes started to emerge, dealers were invited to test drive sessions, and this increased the enthusiasm for the new car. In addition, Ford took some radical measures to reduce the price on the car. As an example, the car was only offered in three exterior colours (black, white and moonstone blue) and one interior colour (grey). There were also just two equipment options: with or without central locking and electric window lifts.

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