It was the result of a Ford Motorsport project with the purpose of producing an outright winner for Group A racing in Europe.

Turner got in touch with Walter Hayes, at the time the vice-president of public relations at Ford, to get support for the project.

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.

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.

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.

Experience had shown that the Sierra hatchback body generated significant aerodynamic lift even at relatively moderate speed.

In 1984, Walter Hayes paid visits to many European Ford dealers in order to survey the sales potential for the Sierra RS Cosworth.

The Ford Sierra RS Cosworth was first presented to the public at the Geneva Motor Show in March 1985, with plans to release it for sale in September and closing production of the 5,000 cars in the summer of 1986.

The following number of vehicles were registered in the UK: As published in the 1986 RS catalog: Mike Moreton was head of the team that planned to develop an evolution edition aimed at making the car unbeatable on the race tracks.

The rear-drive car never won a loose-surface World Rally Championship event, but in the hands of drivers such as Stig Blomqvist, Carlos Sainz and Ari Vatanen it frequently finished in the top five, except when conditions were particularly slippery.

On tarmac it was a much more serious competitor, and a young Didier Auriol won the 1988 Corsica Rally outright, the only time that season that Lancia were beaten in a straight fight.

However, as Lancia developed the Delta Integrale further and new cars such as the Toyota Celica GT-Four ST165 appeared, the Cosworth became steadily less competitive.

Thanks to strong support and readily available parts from Ford Racing, the Cosworth was a popular car with private teams.

Moreover, below world championship level, four-wheel-drive opposition was limited at the time, and the Cosworth was as fast as any of its two-wheel-drive rivals.

The second generation four-door Sierra Sapphire Cosworth was assembled in Genk, Belgium, with the UK-built Ford-Cosworth YBB engine.

Suspension was essentially the same with some minor changes in geometry to suit a less aggressive driving style and favour ride over handling.

Specifically the left hand drive models (LHD) which saved weight with a lesser trim level such as roll up rear windows, no air conditioning etc.

"Sapphire" being viewed as a Ghia trim level that saw power rear windows, air conditioning and other minor options.

It was therefore decided that the new car should be a natural development of the second generation, to be launched in conjunction with the face lift scheduled for the entire Sierra line in 1990.

The waiting time gave Ford Motorsport a good opportunity to conduct extensive testing and demand improvements.

It was not a great success and never won a World Championship event, although in the hands of drivers such as François Delecour and Massimo Biasion it did take several second and third places.

Initially it was unreliable, the gearbox being an especially weak point, and although by 1992 the reliability problems had been solved the Cosworth was never quite as effective in most conditions as some of its rivals.

It was a relatively large car, slightly heavy, and less sophisticated than the latter generations of the Lancia Delta and Toyota Celica in terms of transmission systems and electronics.

By then technical development of the Sierra had ceased, and most of the team's effort was directed towards the upcoming Escort Cosworth, which promised to be a much more competitive prospect.