1988-9; approximate number built: 13,140; also badged without RS and Sapphire in LHD; front engine, rear-wheel drive, assembled at Genk with UK-built Ford-Cosworth engine; rear drive only, BWT5 five-speed.

Type: Ford Cosworth YBB. Capacity: 1993 cc. Bore/stroke: 90.82 mm/76.95 mm. Compression ratio: 8:1. Max power: 204 bhp DIN at 6,000 rpm. Peak torque: 205 Ib/ft (276 Nm) at 4,500 rpm. Specific output: 102.4 bhp per litre. Power/weight ratio: 165.9 bhp/tonne. Cylinders: four, in line. Cylinder head: Cosworth cast alloy, 16v, DOHC. Block: Cast iron. Valve gear: four valves per cylinder twin overhead camshafts with toothed belt-drive. Fuel & ignition: Weber-Marelli microprocessor-managed fuel injection. Garrett AiResearch T03B turbocharger with intercooling, breakerless ignition.

Type: Front engine, rear drive, Viscous Coupling limited slip rear differential, single plate, 240 mm, diaphragm spring clutch. Gearbox: Borg Warner T5. Internal ratios: As for original 3-dr and RS500. Final drive: 3.64:1, 22.8 mph per 1,000 rpm in 5th.

MacPherson strut front, trailing arm rear, gas damping, anti-roll bars (28 mm and 16 mm), principles as before, but 1987 specification rear roll bar mounting and unique spring/damper settings.

Type: Power assisted, Cam Gears/TRW rack and pinion, lock to lock: 2.6 turns

Front: 283 mm, vented discs. Rear: 273 mm solid back discs. System: Hydraulically assisted, Alfred Teves GmbH electronic anti-lock action.

Wheels: Unique Ford Design 7J x 15 alloys, new Tyres: Dunlop D40 205/50 VR

Type: Sapphire 4-dr saloon in Ghia trim, but 170 mph speedometer and no tachometer redline, unique body colour-matched front grille bumper/air dam, rear· 'hoop' spoiler and side sill extensions by Marley. Cd: 0.33. Dimensions: As for 1986 RS Cosworth 3-dr, but length 176 in (4,460 m); width 67 in (1,700 mm); weight 2,750 lb (1,250 kg).

(Manufacturer's figures) Max speed: 151.4 mph (243.6 km/in) Acceleration: 0 60 mph, 6.1 see; 30 50 mph (4th/5th gear) 6.5/11.0 sec. Fuel consumption: 22.1 mpg, urban; 35.3 mpg at constant 56 mph; 27.7 mpg at 75 mph.

For turbo longevity it is recommended that the Sierra Cosworth along with all other turbocharged RS models run with fully synthetic oil. These types of oil give the necessary engine protection for the high temperatures attained in turbocharged vehicles

4WD PRODUCTION SPECS:

1990-92; approximate number built: 12,250; assembled at Genk, Belgium using UK-built engine, and Ferguson patented 4x4 transmission with Ford MT75 gearbox.

ENGINE

Type: Ford Cosworth YBJ/YBG.#

Capacity: 1993 cc.

Bore/stroke: 90.82 mm/76.95 mm.

Compression ratio: 8:1.

Max power: 220 bhp at 6,000 rpm (6,250 rpm with Cat).

Max torque: 214 lb ft at 3,500 rpm.

Specific output: 110.4 bhp a litre.

Power/weight ratio: 174.6 bhp per ton.

Cylinders: four, in line.

Cylinder head: stiffened cast alloy.

Block: Modified Pinto/RS500 iron casting.

Valve gear: Cosworth four valves per cylinder head, double overhead camshafts (DOHC) of revised profiles, belt-drive.

Fuel and ignition: Weber-Marelli ignition/fuelling management, Garrett TO3B turbocharger with lead seal for wastegate and enlarged intercooler.

# The YBJ was the red rocker cover Euro 1504 Emission trim; YBG was to the more restrictive US '83 emissions level. Significant 4x4 YBJ/YBG motor changes included: inlet manifold/fuelling rail; replacement cast iron exhaust manifold (no damper); oil and water pumps; cast alloy sump pan; head gasket; first platinum-tipped Motorcraft spark plugs (AGPR 902P) and synthetic oils only.

TRANSMISSION

Type: Front engine, permanent 4WD, Ferguson 4WD/Viscous Coupling patents, 4x4 utilized 34-66 per cent front-rear torque split via transfer box epicyclic centre differential, further modified by Viscous Coupling action, front drive via Hyvo chain, 31 tooth chain wheels, 6.5 in spiral bevel gear free differential and equal length drive shafts, to the rear by gear output shaft, propshaft, 7 in hypoid Viscous Coupling limited slip rear axle, single dry plate clutch, cable operation, 240 mm (9.5 in).

Gearbox: Five-speed Ford MT75.

Internal ratios: 1st, 3.62; 2nd, 2.08; 3rd, 1.36; 4th, 1:1; 5th, 0.83.

Final drive: 3.62:1, 22.24 mph per 1,000 rpm in 5th.

SUSPENSION

Front: Via MacPherson struts, unique RS spring rates, monotube gas damping, thickened (30 mm) anti-roll bar.

Rear: Separate springs and single tube gas dampers, plus 18 mm rear anti-roll bar, spring rates as per previous 2WD Cosworth

STEERING

Type: Hydraulic power assistance, rack and pinion, lock-to-lock: 2.6 turns.

BRAKES

Front: 278 x 24 mm (10.94 x 0.94 in).

Rear: 273 x 20 mm (10.74 x 0.79 in).

System: Four wheel ventilated discs with Teves ABS electronic anti-lock braking and hydraulic assistance.

WHEELS AND TYRES

Wheels: Unique RS 7 x 15 in alloys.

Tyres: Bridgestone ER90 205/50 ZR 15 on UK cars.

BODY

Type: Sierra 4-dr.

Cd: 0.322. 1

Construction: Unitary steel with RS polyurethane panels including front and rear spoilers, side sills and bonnet louvres. Dimensions: Overall length: 4,494 mm (176.9 in); width, 1,698 mm (66.8 in); height, 1,376 mm (54.2 in); wheelbase, 2,608 mm (102.7 in); kerb weight: 1,280 kg (2,816 lb), add 10 kg (22.05 lb) for Cat model.

PERFORMANCE & ECONOMY (Manufacturer's figures)

Max speed: 150 mph.

Acceleration: 0 60 mph, 6.6 sec.

Fuel consumption: 22.1 mpg urban; 37.2 mpg at constant 56 mph; 30.4 mpg at 75 mph.