When Ford teamed up with Cosworth Engineering to breathe life onto its humdrum Sierra, few knew it would be the birth of a motoring legend. Through circuit racing and supercar-humbling on-road ability, the 1985 Sierra RS Cosworth quickly became a household name.

A practical four-seater boasting 204bhp from its two-liter turbocharged power plant, the RS Cosworth's massive performance was equaled only by an extroverted rear wing designed for high-speed stability
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While motorsport machines scooped innumerable victories and increasingly powerful engines, in 1987 Ford homologated a yet-more-spectacular Sierra - the 224bhp RS500. It instantly became a desirable collector's piece.

The restrained four-door Sierra Sapphire RS Cosworth of 1988 was Ford's vision of a 150mph executive express; two years later, its four-wheel-drive successor returned the firm to rallying. By 1992, Ford had squeezed the 4x4's running gear into a shorter Escort body, complete with 227bhp engine and ever-more-aggressive aerodynamic aids.

The limited-edition Monte Carlo came in 1994, followed by the final RS Cosworth - a revised Escort with smaller turbocharger and user-friendly appeal. Production ceased in 1996. Today, each model has a loyal following among motorsport fans and fast Fords enthusiasts. And as the cars become increasingly sought-after, so too does the pursuit of perfection.

This book examines RS Cosworth authenticity, outlining standard specifications alongside in-depth color photography of outstanding examples of the breed. From body panels and trim to turbochargers and tires; from interior fabrics and paint schemes to shock absorbers and stickers, Ford's factory-original fitments are covered in comprehensive detail.

Ford Escorts have been a fixture in Dan Williamson's life for longer than he remembers. Early childhood spent sliding across the seats of his dad's GT-engined Mk1 instilled an anorak-level addiction to fast Fords. Like most Escort enthusiasts, his condition is incurable. Dan was given his first car when he was 15, a 1972 Mk1 that's perhaps best described as a long-term project. It currently shares garage space with a '71 Mexico, a 1600 Sport and a variety of other Fords, from modern STs to a pair of RS Cosworths. Dan trained as a newspaper reporter before becoming a motoring journalist in 1997, working for the UK's leading automotive publishers - a role that involved driving (and owning) many of the models in this book. Today he's an editor and contributor to a variety of magazines, including Fast Ford and Classic Ford. Dan lives in rural Lincolnshire, where he dreams about discovering a barn-stored RS1800. Don't we all...

Simon Clay is a freelance photographer specializing in cars, people, and architecture. He trained at Bournemouth & Poole College of Art, and from 1990 to 1996 was employed full-time as the photographer for England's National Motor Museum at Beaulieu.