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 . 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.