The history of the RS Cosworths starts at the moment Ford decided to put a turbo onto the old trusty Pinto block and install it in the Sierra RS Cosworth. That was back in 1985 and the engine produced 204 hp. The Sierra RS Cosworth was first produced in 1986 as an homologation special for rallying. 5000 examples was required to get a car homologated for group A. It was not particularly successful, mostly due to the lack of four wheel drive; no wins in group A rallying But it did have a certain amount of success in touring car championships.

Then there was the Sierra RS500. Based on 500 examples of the Sierra RS Cosworth 394 were black 52 were moonstone blue and 56 in white including 4 prototypes, these were converted by aston martin tickford on behalf of ford. The RS 500 had different spoilers to aid downforce and 224hp. An extra air intake above the numberplate and the extra tip on the rear spoiler are the easiest way of distinguishing it from a standard Sierra Cosworth. Only twenty more bhp was produced from the following additions: Garrett T4 turbocharger, much larger intercooler, 8 injectors (only 4 were used on the standard car), 9mm bigger intake manifold and thicker engine block walls. In race trim these engines were producing in excess of 500 bhp!!  Probably Ford's most successful car to date it did win the only World touring car championship that was ever held.It also had 40 victories in row in the BTCC. Arguably the most sought after cosworth ford.

When the required 5000 examples of the three door Sierra RS Cosworth were produced Ford felt that they needed a car with the same amount of power but with more comfort and ability to carry the family too. The answer to these requirements was the rear-wheel-drive Ford Sierra Saphire Cosworth. It used a standard 4 door sierra body with the the same engine, suspension and drivetrain as the 3-door Sierra RS Cosworth. the body was modified slightly from the standard Sierra with different bumpers incorparating fog lights, and a new lower lip on the front bumper. A rear boot spoiler was also added to counter aerodynamic lift at high speeds.

After the RS500 there was an empty slot in the Ford motorsport department. They needed a new car to keep up with the Lancia Delta HF Integrale and the Audi Quattro. This lead to the development of the 4-door Sierra RS Cosworth 4wd. It looked very similar to the Saphire 2wd, but underneath the body the changes were vast. It had Ferguson 4 wheel drive system with two viscous couplings; one on the center diff, the other on the rear diff. Torque split was 34% to the front and 66% to the rear wheels. The engine was improved, having changed 80% of the parts compared to the Saphire Cosworth. The changes included new stronger blocked known as the 200 , stronger head and stronger pistons with new gudgeon pin placement to decrease piston slap. A new Garrett T03 turbo, new intake manifold and bigger intercooler were also installed. This lead to a power increase to 220bhp, performance remained unchanged due to the cars extra weight but much more was available when tuning the engine. But none the less; it still did not fulfill Ford's expectations. It did not score a single group A win in it's two years of rallying. The reason the Sierra Saphire didn't produce any decent results was probably due to it's weight and size. Ford simply needed a smaller car. The suitable model for the time was the Escort.

But there was no Escort that could be homologated as a rallycar as it had to have turbo and four wheel drive. So a new variation of the Escort model had to be produced. Ford knew they had a great engine in the YBG that sat in the the Sierra Saphire, so Ford's master plan was to simply put the engine, drivetrain and suspension of the Sierra Saphire 4wd into a modified and strengthened Escort shell. But, to Ford's dismay I suppose, it was simply not possible so a new chassis and body had to be built specifically for the Escort RS Cosworth. After 400 new parts a new car was born: more than twice as stiff and strong a standard Escort Chassis. The Escort Cosworth shares only 50% of it's body panels with the standard Escort. The most prominent features of the new body is: New hood with two vents helping in the removal of hot air from the engine compartment. New wider front arches with air exits from the engine in front of the doors. New wider rear wheelarches. New Front bumper with huge air intakes and low front spoiler with adjustable splitter. New low rear bumper. All this creates a car that not only counters the aerodynamic lift at high speeds but creates downforce too. At 180km/h the downforce is 45N at the front, with the splitter at it's middle position, and 190N at the rear.
Ford did not have the space to build the Escort Cosworth, so the car was put together by Karmann in Germany. The production of the Escort Cosworth started on the 19th of February 1992.
The Escort RS Cosworth was Ford's new rallycar and was much more successful at it than it's earlier brothers; the Sierra Cosworth in two and four wheel drive versions. The total count of victories came to 8 in group A, and after the modifications that were made to the car to make it a WRC car, it scored two more victories.
In 1994, after the 2500 cars required for homologation were produced Ford put a "new", more civilized engine into the Escort Cosworth. The new engine is basically the same old engine in a new package. It has smaller turbo (Garrett T25) and fords own eec4 engine management system. This lead to more low-rew punch, but less boost available above 5500rpm. The new Escort RS Cosworth was produced until early in 1996 when EU put a new set of noise regulations for cars to work, and the Escort Cosworth couldn't pass those without modifications. For some reason Ford then decided to stop the production instead of changing the car so it would be within the new noise regulations. And that was the end to the Escort RS Cosworth. The last car rolled out of the factory on the 12th of January 1996. Then 7.145 Escort Cosworths had been produced.