The vehicle shell was based on the bottom of the range 3 door Sierra shell retaining the basic two rear side windows and two front doors. The dashboard was taken from the American Sierra XR4Ti which included the turbo boost gauge. Design knowledge was similarly taken from the American Sierra XR4Ti Merkur. The car was designed by Ford's Special Vehicle Engineering (SVE) group and manufactured at Ford's Genk, Belgium operation. The Sierra Cosworth was launched in July 1986 and 5545 were manufactured in total of which 500 were sent to Tickford for conversion to the Sierra 3 door RS500 Cosworth. The vehicle was manufactured in both RHD (Right Hand Drive) for the UK market, and LHD (Left Hand Drive) for Europe. The following number of vehilces were registered in the UK:

1985     10
1986   1064
1987    579
Total: 1653

Many of these cars were used very successfully for racing, in both rally and road events:

Development of the Cosworth engine was started way back in 1982 on a non-turbo, 16-valve, Dual Over Head Cam (DOHC) version. This version was coded YAA. Ford planned to use this engine, but TURBOcharged it!

This turbo version became the first Ford Cosworth engine and was coded YBB (nothing like a logical naming convention). The first production began in 1987 after further development of the engine by Cosworth. The first engines to be used by Cosworth in the two wheel rear drive (3 door) Sierra was coded YBD and had a measured output of 204 bhp at 6000 rpm. Peak torque was 203 lbs ft at 4000 rpm. No diesels here!

The engine specifications were:

Displacement:

1993 cc

Bore:

90.8 mm

Stroke:

77 mm

Compression Ratio:

8.0:1 with pentroof combustion chambers

Inlet Valves

35mm operated via bucket tappets

Exhaust Valves

31mm (sodium cooled) operated via bucket tappets

Cam shafts

Running five bearings

Turbocharger:

Garrett AirResearch TO3 unit with integral waste gate and water cooled centre-housing. As originally fitted to the MK3 Escort Series 1 Turbo.

Turbo boost pressure:

9 psi

Injection and Ignition system:

Weber-Marelli multi-point fuel injection

Oil Cooler

Water to oil intercooler mounted on the side of the block

Both crankshaft and conrods were heat-treated steel items to add further strength to the engine.

The turbocharger also used a dump valve which let the turbo keep spinning when the throttle was released. Thus improving the engines response times. The TO3 turbo was mounted on top of the high nickel content exhaust manifold. A special mounting plate was used to allow the turbo to grow as it got hotter without cracking or causing undue stress.

The compressed air exiting the turbo was feed to an air-to-air intercooler mounted next to the engine coolant radiator.

Cosworth chose belt drive for the twin overhead cam engine. These Uniroyal rubber reinforced fibreglass items were used to power the oil pump and distributor.

The engine also used a high pressure oil pump needed to feed the spray jets, which pointed underneath the Mahle forged piston crowns.

(The engine and turbo system had great tuning potential as detailed in the MK4 Escort Series 2 Turbo page.)

The engine was coloured red to indicate it could be run on Four Star leaded petrol.

All Cosworth engines are fitted with hardened valve seat inserts and can therefore run continuously on unleaded fuel. With ordinary unleaded petrol it is necessary to retard the ignition by 4 Degrees. A power loss of approximately 10 bhp will be experienced after the ignition is retarded. Retarding the ignition may not be necessary if the engine is always run on Super unleaded fuel.

This took the Ford Sierra from being a boring rep-mobile into a fire breathing road rocket. This set Cosworth and Ford on a ten year path together producing one of the best affordable super cars.

• Sierra 3 door RS500 Cosworth
• Sierra Sapphire 2WD Cosworth
• Sierra Sapphire 4WD Cosworth
• MK5 Escort RS Cosworth

This Cosworth engine, like its turbocharged stable mate the MK3 Escort Series 1 Turbo, used a sophisticated engine management system. This system controlled:

• Ignition timing
• Fuel injection used Weber/Marelli equipment
• Fuel pressure
• Turbo boost pressure

The Sierra Cosworth used a five speed manual gearbox mounted at the rear of the engine. This fed the prop shaft which then fed power via the rear differential to the back wheels. The gearbox was a Borg-Warner T5 5-speed unit taken from the 2.3 Turbo Mustang with a modified 5 gear ratio. The rear differential was a Ferguson-type 7.5 inch viscous unit.

The 11.1 inch brake front disks were 0.94 inches thick and used Ferodo F3432 pads. The front calipers were high performance four pot items.

Steering was non power-assisted and used a rack and pinion. Front suspension was via independent MacPherson struts with anti-roll bar. Dampers were gas filled twin tube units from Fichtel and Sachs, the preferred supplier to the Ford SVE group for all Ford Cosworths.

The rear suspension used much of the Sierra XR4 4WD layout. It used trailing rear arms with uniball joints and again Fichtel and Sachs gas filled damper units.

With the Sierra's huge whale tail this car could not be described as a street sleeper by any stretch of the imagination. Much design had gone into this rear fin to produce a large down force. The down force was measured at 164 Nm (124 mph wind tunnel test) compared with the standard 3 door Sierra's of 513 Nm UPLIFT!

Available colours where:

• Black
• White
• Moonstone Blue

BBS style Rial manufactured alloy wheels sported the new Dunlop D40 205/50 x 15 VR low profile tyres.

This Sierra Cosworth featured colour coded bumpers, side skirts and mirrors. Driving lamps mounted within the front spoiler came as standard.

In 1987 a limited edition uprated version of this Sierra Cosworth was produced, it was named the RS500 since only 500 were produced.

The Sierra Cosworth 3 door was produced from 1986 to 1988, when the Sierra Sapphire 2WD Cosworth based on the new design Sapphire 5 door shell replaced it.

UK price guide (Sterling)

Condition       Excellent   Good    Average

Sterling         10000      9000     7500

Note: The FORD Sierra Cosworth 3-door was produced on C to E-registration plates in the UK.

For further details see Vehicle Registration Plate Guide.

NOTE: 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. The following viscosity synthetic oils are recommended: 5w50, 10w40, 15w50, 10w60.

The Sierra Cosworth was based on the Sierra of the time. Further details of which can be found in the Ford Sierra 1982 Workshop manual.