Together, Ford and Cosworth released the Sierra Cosworth RS as a homologation special for Group A rally. Thankfully 5000 examples were needed for homologation into Group A rally and by 1986 the car went into regular production.
The Cosworth-developed YBB engine was a Pinto-based block with a Cosworth aluminum head. It was equipped with an intercooled Garret AirResearch TO3 turbocharger that delivered 9psi of boost, resulting in just over 200 horsepower. While for a road car this power was exceptional, especially given the price, in motor sport it was not ample. Given the fact that the car was also rear-wheel-drive and suffered from turbo lag, it is no surprise it didn’t take any outstanding victories in Group A.
Although unsuccessful in rally, the RS Cosworth was quite capable on the road. It even out-powered and weighed less than the BMW’s E30 M3. As a result the car achieved a top speed of 150 mph with a sub six second run to sixty mph.
Based in the RS Cosworth, 500 special RS500 models were built with a more powerful engine. Eventually the whole project evolved into the Escort Cosworth RS which was a more purpose built machine.