Ford Sierra RS Cosworth

The history of the Ford Sierra RS Cosworth


The project was defined by Stuart Turner in the spring of 1983. He had then recently been appointed head of Ford Motorsport in Europe, and he realized right away that Ford was no longer competitive in this area.
Turner got in touch with Walter Hayes, at the time Vice President of Public Relations at Ford, to get support for the project. Hayes had earlier been the driving force behind the development of the Ford GT40 that won Le Mans in 1966, and the Cosworth DFV engine that brought Ford 154 victories and 12 World Championships in Formula One during the Sixties and Seventies. Hayes found the project very appealing and promised his full support.
Turner then invited Ken Kohrs, Vice President of Development, to visit Fordís long time partner, the automotive company Cosworth, where they were presented a project developed on Cosworthís own initiative, the YAA engine. This was twin cam, 16-valve engine based on Fordís own T88 engine block, better known as the Pinto. This prototype proved an almost ideal basis for the engine Turner needed to power his Group A winner.
Therefore, an official request for a turbocharged version (designated Cosworth YBB) capable of 180 HP on the street and 300 HP in race trim, was placed. Cosworth answered positively, but they put up two conditions: the engine would produce not less than 150 kW (204 HP) in the street version, and Ford had to accept no less than 15,000 engines. Turnerís project would only need about 5,000 engines, but Ford nevertheless accepted the conditions. The extra 10,000 engines would later become one of the reasons Ford also chose to develop a four door, second generation Sierra RS Cosworth.
To find a suitable gear box proved more challenging. The Borg-Warner T5, also used in the Ford Mustang, was chosen, but the higher revving nature of the Sierra caused some problems. Eventually Borg-Warner had to set up a dedicated production line for the gear boxes to be used in the Sierra RS Cosworth.
Many of the suspension differences between the standard Sierra and the Cosworth attributed their development to what was learned from racing the turbocharged Jack Roush IMSA Merkur XR4Ti in America and Andy Rouse's successful campaign of the 1985 British Saloon Car Championship. Much of Ford's external documentation for customer race preparation indicated "developed for the XR4Ti" when describing parts that were Sierra Cosworth specific. Roush's suspension and aerodynamics engineering for the IMSA cars was excellent feedback for Ford. Some production parts from the XR4Ti made their way into the Cosworth such as the speedometer with integral boost gauge and the motorsport 909 chassis stiffening plates.
In April 1983, Turnerís team decided on the Sierra as a basis for their project. Sierra filled the requirements for rear wheel drive and decent aerodynamic drag. A racing version could also help to improve the unfortunate, and somewhat undeserved, reputation that Sierra had earned since the introduction in 1982.
Lothar Pinske, responsible for the carís bodywork, demanded carte blanche when it came to appearance in order to make the car stable at high speed. Experience had shown that the Sierra hatchback body generated significant aerodynamic lift even at relatively moderate speed.
After extensive wind tunnel testing and test runs at the NardÚ circuit in Italy, a prototype was presented to the project management. This was based on an XR4i body with provisional body modifications in fibreglass and aluminium. The carís appearance raised little enthusiasm. The large rear wing caused particular reluctance. Pinske insisted however that the modifications were necessary to make the project successful. The rear wing was essential to retain ground contact at 300 km/h, the opening between the headlights was needed to feed air to the intercooler and the wheel arch extensions had to be there to house wheels 10Ē wide on the racing version. Eventually, the Ford designers agreed to try and make a production version based on the prototype.
In 1984 Walter Hayes paid visits to many European Ford dealers in order to survey the sales potential for the Sierra RS Cosworth. A requirement for participation in Group A was that 5,000 cars were built and sold. The feedback was depressing. The dealers estimated they could sell approximately 1,500 cars.
Hayes didnít give up however, and continued his passionate internal marketing of the project. As prototypes started to emerge, dealers were invited to test drive sessions, and this increased the enthusiasm for the new car. In addition, Ford took some radical measures to reduce the price on the car. As an example, the car was only offered in three exterior colours (black, white and moonstone blue) and one interior colour (grey). There were also just two equipment options: with or without central locking and electric window lifts.
Ford Sierra RS Cosworth was first presented to the public on the Geneva Motor Show in March 1985, with plans to release it for sale in September and closing production of the 5,000 cars in the summer of 1986.
In practice, it 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.
Mike Moreton was head of the team that planned to develop an evolution edition aimed at making the car unbeatable on the race tracks. In March 1987, Aston Martin in Tickford was signed for the job of converting the 500 cars.
The Cosworth RS500 was announced in July 1987 and was homologated in August 1987.
The main difference to the Sierra 3 door Cosworth was the uprated Cosworth competition engine. Its new features were:
The engine had a thicker walled cylinder block to cope with the rigours of the track.
A larger Garrett T31/T04 turbocharger.
A larger air-air intercooler.
A second set of 4 fuel injectors and a second fuel rail (unused in the roadgoing version).
The fuel pump was uprated.
A reworked induction system to allow higher power outputs to be realised.
The oil and cooling system were both also uprated.
The rear semi-trailing arm beam had extended but unused mounting points.
The RS500 also had minor external cosmetic differences to its parent the Sierra 3 door Cosworth:
The rear tail gate had a lower spoiler in additional to the upper whale tail, which had an added lip.
Discrete RS500 badges on the rear tail gate and front wings.
A redesigned front bumper and spoiler to aid cooling and air flow, including the removal of the fog lamps and their replacement with intake grilles to supplement brake cooling
Exactly 500 RS500s were produced, all of them RHD for sale in the UK only - the biggest market for this kind of Ford car. It was originally intended that all would be black, but in practice a few white and Moonstone Blue cars slipped through.
The second generation 4 door Sierra Sapphire Cosworth was assembled in Ghenk, Belgium, with the UK-built Ford-Cosworth YBB engine. Cylinder heads on this car were early spec 2wd heads and also the "later" 2wd head which had some improvements which made their way to the 4X4 head. Suspension was essentially the same with some minor changes in geometry to suit a less aggressive driving style and favour ride over handling. Spindles, wheel offset and other changes were responsible for this effect. Approximately 13,140 examples were produced during 1988-1989 and were the most numerous and lightest of all Sierra Cosworth models. Specifically the LHD models which saved weight with a lesser trim level such as roll up rear windows, no air conditioning etc.
In the UK, the RHD 1988-1989 Sierra Sapphire RS Cosworth is badged as such with a small "Sapphire" badge on the rear door window trims. All 1988-1989 LHD models are badged and registered as a Sierra RS Cosworth with no Sapphire nomenclature at all. "Sapphire" being viewed as a Ghia trim level that saw power rear windows, air conditioning and other minor options. Enthusiasts of the marque are mindful of this and will describe the LHD cars by their body shell configuration, 3 door or 4 door.
In January 1990 the third generation Sierra RS Cosworth was launched, this time with four wheel drive. As early as 1987, Mike Moreton and Ford Motorsport had been talking about a four wheel drive Sierra RS Cosworth that could make Ford competitive in the World Rally Championship. The Borg Warner T75 gear box that was considered an essential part of the project wasnít available until late 1989 however.
Ford Motorsportís desire for a 3-door ďMotorsport SpecialĒ equivalent to the original Sierra RS Cosworth was not embraced. The more discreet 4-door version was considered to have a better market potential. It was therefore decided that the new car should be a natural development of the second generation, to be launched in conjunction with the face lift scheduled for the entire Sierra line in 1990.
The waiting time gave Ford Motorsport a good opportunity to conduct extensive testing and demand improvements. One example was the return of the bonnet louvers. According to Fordís own publicity material, 80% of the engine parts were also modified. The improved engine was designated YBJ for cars without a catalyst and YBG for cars with a catalyst. The latter had the red valve cover replaced by a green one, to emphasize the environmental friendliness. Four wheel drive and an increasing amount of equipment had raised the weight by 100 kg, and the power was therefore increased to just about compensate for this.
The Sierra RS Cosworth 4x4 received, if possible, an even more flattering response than its predecessors and production continued until the end of 1992, when the Sierra was replaced by the Mondeo. The replacement for the Sierra RS Cosworth was not a Mondeo however, but the Escort RS Cosworth. This was to some extent a Sierra RS Cosworth clad in an ďEscort-likeĒ body. The car was released in May 1992, and was homologated for Group A rally in December, just as the Sierra RS Cosworth was retired.

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