Ford Sierra RS Cosworth

Start with identity, paperwork and originality. For the Ford Sierra RS Cosworth, the strongest cars have a continuous ownership file, matching numbers where applicable, original manuals, invoices and evidence of work by recognised marque specialists. Originality of body, low mileage, original colour combination, RS Owners Club documentation and continuous service history are decisive.

The Cosworth YB engine is robust when correctly maintained; turbo health, cooling, ignition mapping and gearbox condition are core items. A proper pre-purchase inspection includes cold-start behaviour, leak-down or compression testing where appropriate, underbody photography, suspension and chassis-point inspection, brake condition and a road test long enough to expose heat-related faults. Deferred maintenance is almost always more expensive than buying a better-sorted car.

Use a paint-depth gauge, lift access and a specialist familiar with the model's factory seams and panel gaps. Collector value is dramatically affected by structural repairs, poor paintwork, corrosion, incorrect panels and missing factory trim. Documented cosmetic restoration is acceptable; concealed accident repair must be priced severely.

RS500 (500 built) is the apex; three-door Cosworth and 4x4 Sapphire are the usable collector tiers; standard Sapphire RS Cosworth (RWD) is the entry. Specification, colour, transmission and limited-build variants move values significantly. Buy the best-documented example in the most desirable specification you can justify rather than a tired example of a rarer derivative that will need years of corrective work.