Oct 18

Oct 18 Guide: Wild One Refined - a Historical & Technical Appraisal of the Ford Sierra Sapphire RS Cosworth (1988-1990)

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BACKGROUND

Announced in February 1987, the second generation Sierra was conceived as a more conventionally-styled successor to the avant garde, highly aerodynamic original that had in turn replaced the long-running Cortina.

Perhaps most significantly, unlike the original Sierra (which had been offered exclusively as a Hatchback or Estate), this latest iteration would also be sold as a Saloon after the lack of such a version had meant conservative mid-range buyers frequently looked elsewhere. Customers could thus specify a five-door Hatchback, a five-door Estate or a four-door Saloon, but the increasingly unpopular three-door Hatchback was dropped.

Up until the end of 1987, Ford’s top-of-the-range Mk2 Sierra was the XR4x4, a five-door Hatchback powered by a 2.9-litre 148bhp normally aspirated V6. However, the XR4x4’s rein as the flagship Sierra was extremely brief; in the background, Ford’s engineers were working on a much more potent Cosworth-powered version to replace the heavily spoilered original produced until the summer of 1987.

Unlike the Mk1 Sierra Cosworth which Ford manufactured in order to go Group A Touring Car racing, this latest iteration, announced in November 1987, was not created to meet a set homologation requirement. Instead, it principally served to use up the remaining stock of Cosworth YBB engines as Ford had been forced to order 15,000 of the things and only 5000 of the hot first generation Sierras had been required for Group A homologation.

Nevertheless, this second generation Sierra Cosworth proved sufficiently popular (in part thanks to its more practical four-door configuration) that Ford had to go and order even more of the YBB units from Cosworth around twelve months after launch.

Production of the new model began at Ford’s Ghenk plant in Belgium during January 1988. Engines were shipped across the British channel from Cosworth’s facility in Northampton. In different markets the car was variously dubbed Sierra Cosworth, Sierra RS Cosworth and Sierra Sapphire RS Cosworth.

CHASSIS

Each Mk2 Sierra Cosworth was based on a galvanised steel bodyshell with an identical 2608mm wheelbase to the original three-door Hatchback variant. Similarly, a 60-litre fuel tank located under the trunk floor was carried over.

Suspension was once again via MacPherson struts with lower control arms at the front and semi-trailing arms at the rear.

To improve handling, these Cosworth variants came with stiffer coil springs, firmer dampers and thicker anti-roll bars. For this latest application, Ford wanted to go for a sightly more compliant ride before so new hub-carrying spindles were adopted along with different wheel offsets.

The wheels themselves were Ford’s brand new cross-spoke 7 x 15 alloys originally mounted on Dunlop D40 205/50 tyres.

As per the Mk1 Sierra Cosworth, a quicker than normal power-assisted steering rack was fitted. Also imported was the special ABS system with 283mm diameter ventilated discs and four-piston calipers up front and 273mm solid discs with single-piston floating calipers at the rear.

ENGINE / TRANSMISSION

In the engine bay was the aforementioned Cosworth YBB water-cooled inline ‘four’ which was itself derived from Ford’s cast-iron T88 Pinto block that displaced 1993cc thanks to a bore and stroke of 90.8mm and 76.95mm respectively.

For the YBB, Cosworth developed a special light alloy head that featured two belt-driven overhead camshafts operating 16 valves (eight 35mm diameter inlet and eight 31mm exhaust).

Mahle pistons with forged steel connecting rods were fitted together with a forged steel crankshaft, a special oil pump, a custom cast aluminium sump and a free-flow exhaust. Cosworth also fitted a Garrett AiResearch T03B turbocharger (set at 0.7 bar) and an an air-to-air intercooler.

Wet-sump lubrication was employed along with an 8.0:1 compression ratio and Weber-Marelli digital engine management with electronic port fuel-injection.

Peak output was 201bhp at 6000rpm and 204lb-ft at 4500rpm.

The YBB motor was the first production car engine to produce more than 100bhp per litre.

To handle all this power and torque, Ford used a beefier gearbox than in the rest of the Sierra range: a five-speed manual Borg Warner T5 which was a specially configured version of the type used in the Mustang.

Transmission was through a hydraulic single-plate clutch and viscous-coupling limited-slip differential.

BODYWORK

In a similar fashion to BMW’s M5, Ford accessorised the Sierra Cosworth with a variety of subtle external details that gave it a sporty but still discrete appearance (adjectives that would never have been used to describe the wild Mk1).

Each Cosworth started life as a standard Ghia-spec. bodyshell. To this Ford added a reprofiled front bumper assembly with enlarged cooling intakes, repositioned fog lights and wraparound chin spoiler.

In between the headlights was a new grille treatment and down each flank were a set of deep new side skirts.

At the back of the car was a new rear bumper complete with a deeper than normal apron. Mounted on the trunk lid was was a rear spoiler.

Aside from the front chin spoiler , running strips and trailing edge of the rear wing, everything was painted body colour whereas on the standard Ghia black plastic was often used.

At 0.33, the new car’s drag coefficient represented a slight improvement over the 0.345 of the original.

Body panels were manufactured from steel with plastic composite bumpers, skirts, door handles, mirror casings and rubbing strips.

INTERIOR

The interiors of these latest Sierra Cosworths were effectively top-of-the-range Ghia specification to which Ford added Recaro front seats, a small diameter leather-rimmed three-spoke steering wheel and a 170mph / 240kmh speedometer.

Halley and Angora fabric upholstery in Raven and Shadow colourways was used for the seats and door panel inserts. The rest of the door panels along with the dash were fashioned from soft-touch grey plastic. Black plastic was used for the dash inserts.

Instrumentation comprised the aforementioned speedometer and a 7000rpm rev counter. In between these were smaller read outs for fuel and water temperature, a digital trip meter plus a bank of warning lights. Unlike the Mk1 Sierra Cosworth, a turbo boost gauge was not fitted.

A manually-operated glass sunroof, electric windows, a leather-covered gear knob and a six-speak audio system were fitted as standard.

OPTIONS

Optional extras included black leather upholstery, air-conditioning, an onboard fuel computer, an electric sunroof, a superior audio system and an alarm.

Dealer-installed options included security glass etching, an immobiliser system and tailored floor mats.