A closer look at the Ford Sierra RS Cosworth

Ford was no stranger to applying a winning motorsport formula to its range of family favourites by the time the Sierra RS Cosworth went on sale in 1986. Cosworth already had a long-standing partnership with Ford that dated back to the truly legendary DFV V8, and its 2-litre twin cam based on the venerable Pinto block would be at the heart of the Sierra RS during its six-year production run. It was also the first time Cosworth appeared in a Ford model name.

The model was born from the desire of Ford motorsport supremo Stuart Turner to build a new Group A racer that could replace the Capri, and the new, lightweight and streamline Sierra was the obvious candidate. What came cemented itself as a favourite for racers, children of the 70s and 80s, and joyriders of the 90s.

Initially utilising the three-door shell, the RS Cosworth road car launched with 204bhp thanks to the turbocharged Cosworth YB motor, plus wider arches, deep front bumper and spoiler, plus, of course, the infamous rear wing. Ford claimed that this generated over 20kg of downforce at 70mph and was essential at speeds of 180mph. Thanks to its success on track – where it immediately started winning in the World Touring Car Championship, BTCC and pretty much everywhere around the world, including on the rally stage – plenty got to test the claim.  

All RS Cosworths were built at Ford’s factory in Genk, Belgium, although 500 were sent to Tickford to be built into the model’s ultimate incarnation: the RS500. These cars featured further styling revisions, including additional boot spoiler, front spoiler and grille treatment to improve air flow to the larger intercooler. A bigger turbo and enhanced induction system helped to up official power of the road cars to 224bhp, but the engine was developed to generate far more. The production cars even had a second set of injectors (for homologation purposes) that were disconnected for road use and motorsport variants ended up generating well over 500bhp. Road cars even had a set of entirely superfluous pickup points welded for the rear suspension, which served only to allow motorsport teams to alter the rear geometry. Good old homologation rules.  

The Borg-Warner T5 gearbox previously found in the Mustang was adapted to suit the RS Cosworth’s higher revving engine, but its suspension didn’t drastically alter from more mainstream models, albeit with uprated components and different geometry: MacPherson struts and anti-roll bar setup at the front, with semi-trailing arms, coilspring, damper and anti-roll bar layout at the rear, plus a viscous limited-slip differential.

Ford broadened the appeal in ’88 with the introduction of the four-door saloon Sapphire RS Cosworth, which in ’90 gained the option of 4x4 (fitted with an MT75 gearbox). The rear-wheel drive models are most easily identifiable by their lack of bonnet louvres. All road models boasted similar performance figures of around 6 seconds to 60mph and a circa 150mph top speed, plus a superb Recaro interior and otherwise limited options. 

Are you a three-door enthusiast, RS500 aficionado or four-door fan? Or perhaps you’re a Lotus Carlton supporter? Tell us your favourite way of transporting the family at speed in the comments below.