Guide: Ford Sierra Cosworth RS500
Background
Ford originally conceived the Sierra RS Cossworth to serve as a Group A homologation special for Touring Car racing. It was developed alongside a spectacular Group B rally car, the RS200, as Ford looked to usher in a new generation of competition cars for the second half of the 1980s.
To qualify for Group A, 5000 examples of the Sierra RS Cosworth had to be produced before the model could go racing. Deliveries began in July 1986 and homologation was approved on January 1st 1987.
The Sierra Cosworth immediately proved itself competitive against the likes of the BMW E30 M3, Mercedes 190 E 2.3-16 and Alfa Romeo 75 Turbo. However, at this stage, BMW clearly had the edge.
Fortunately, in addition to the 5000 cars that had rolled out of the Genk factory in 1986, Ford had created an additional batch of 500 Sierra Cosworths that would subsequently be converted to Evolution trim. It was hoped an even more extreme racing version of the Sierra Cosworth based on this Evolution variant would be able to quash the challenge from BMW.
The Evolution rule was a supplement to the Group A and B regulations of the time. It permitted manufacturers to produce further enhanced Evolution variants of their homologated vehicle every twelve months. A first Evolution was allowed as soon as the initial homologation had been granted. To qualify, 500 Evolution road cars had to be built, once again within a twelve month period.
To devise the specification for this further uprated Sierra (dubbed RS500), Ford turned to Ruedi Eggenberger whose Eggenberger Motorsport team ran the factory Sierras in the World and European Touring Car Championships. Eggenberger proposed a series of improvements that would make the Sierra practically unbeatable on track.
At the heart of the RS500 was an engine that enabled the Group A racing version to produce considerably more power (up from 370bhp to 470bhp). The RS500 also came with a series of modifications to improve cooling and downforce.
In March 1987, Ford signed a production agreement with Tickford; the 500 unfinished cars that had thus far been stored by Ford in Essex would be trucked to Bedworth where they were converted to RS500 trim.
The RS500 programme was publicly announced in July 1987 and the entire production run was completed before the end of that month.
Homologation was approved on August 1st 1987.
All 500 cars were built in right-hand drive and the RS500 was offered exclusively in the UK. Despite a list price that was around 25% higher than a standard Sierra Cosworth, the entire production run sold out quickly.
Engine / Gearbox
In the transition to RS500 trim, it was the Sierra Cosworth's engine that came in for most attention.
To cope with a glut of extra horsepower in competition trim, the original YBB motor was switched to an uprated YBD unit.
The YBD engine had been specially created for the RS500 and featured a reinforced block (still cast-iron) with thicker walls.
Other new equipment included a bigger Garrett AiResearch T04 turbo (instead of the normal T03B unit) plus a larger air-to-air intercooler. Boost pressure was kept at 0.7 bar.
Cosworth also fitted pressurised oil-cooled pistons, uprated oil, water and fuel pumps and beefier (orange) air hoses for the radiator and turbo.
For competition use, a second set of four Weber IW025 fuel-injectors was supplied (making eight in total for a two per cylinder configuratiuon). However, these extra injectors were not connected to the ECU on RS500 road cars.
The ECU itself was re-mapped to suit the new turbo and injection system.
The induction system was reconfigured with a bigger intake plenum which, along with a new secondary fuel rail, required one corner of the battery tray be cut away for installation.
In addition, the RS500 came with a slightly different thermostat housing and alternator bracket.
The RS500's power rating went from 201bhp to 224bhp at an unchanged 6000rpm.
Peak torque was the same as the regular Sierra Cosworth: 204lb-ft at 4500rpm.
Aside from the aforementioned updates, the RS500 and standard Sierra Cosworth were broadly the same. They were both water-cooled inline ‘fours’ fitted with Cosworth’s special DOHC 16 valve light alloy head.
Displacement was 1993cc thanks to a bore and stroke of 90.8mm and 76.95mm respectively.
The connecting rods and crankshaft were manufactured from forged steel. Cosworth had also developed a special cast aluminium sump and a free-flow exhaust.
Wet-sump lubrication was employed along with an 8.0:1 compression ratio and Weber-Marelli digital engine management with electronic port fuel-injection.
Transmission was courtesy of a Borg Warner T5 five-speed manual, a hydraulic single-plate clutch and viscous-coupling limited-slip differential.
Bodywork
To improve cooling and airflow, the RS500 came with a number of special external features that differed from the standard Sierra RS Cosworth.
The front bumper was subtly redesigned to incoporate a slim air intake above the licence plate housing. The fog lights normally located inboard of the indicators were deleted in favour of supplementary cooling ducts for the brakes. Boxed fog lights were supplied with each car for installation by the dealer if required.
To improve downforce, the RS500 came with a revised aero kit. At the front was a new wraparound chin spoiler with pronounced splitter. At the back, the trademark Whale Tail spoiler was given a thicker trailing edge. A secondary spoiler was added above the tail fascia – in order to ensure the radio antenna did not foul this when opened, a safety switch automatically lowered the aerial.
A discrete RS500 decal was added to the tailgate and every car came with a coachline down each flank.
Originally, Ford intended to paint the entire run of RS500s Black. However, Diamond White and Moonstone Blue cars were also produced as the Genk factory didn't have sufficient numbers of Black cars.
Chassis
For competition use, the RS500 was given rear semi-trailing arms beam with extended mounting points but, like the dual injection system, this was present but unused for road-going versions.
The rest of the specification for the chassis, suspension, brakes, wheels and fuel tank was unchanged.
Each RS500 started life as a standard Sierra bodyshell with a 2608mm wheelbase.
Suspension was via MacPherson struts with lower control arms at the front and semi-trailing arms at the rear.
Compared to other Sierras, the Cosworth variants came with stiffer coil springs, firmer dampers and thicker anti-roll bars. The front anti-roll bar used on the RS500 was the H14 type used by later iterations of the standard Sierra Cosworth.
Sierra Cosworths also came with a quicker power-assisted steering rack and a special Anti-lock Brake System developed in conjunction with ATE.
283mm diameter ventilated discs and four-piston calipers were mounted up front.
The bank end ran 273mm solid discs with single-piston floating calipers.
Rial 15 x 7 cross-spoke alloy wheels had a four stud fixing concealed with a centre cap that gave the appearance of a centre-lock effect. Dunlop tyres were originally fitted and track was 16mm wider at the rear of the car.
A standard 60-litre fuel tank was located in the boot floor.
Interior
Inside, nothing was changed from the original Sierra Cosworth.
The trademark Recaro seats were retained along with a small diameter leather-rimmed three-spoke steering wheel. There was also a turbo boost gauge not found on regular Sierras.
Otherwise, the specification was by-and-large to Ford’s top-of-the-range Ghia equipment level.
Velour seats were trimmed with red and black-patterned centres and grey fabric elsewhere. This same red and black pattern was applied to the velour door panels and rear side panels. The split rear seats could be lowered to provide an enormous load area.
The hard grey plastic dash was home to an instrument binnacle directly behind the steering wheel and a centre console that was angled towards the driver.
Instrumentation comprised large analogue read outs for road and engine speed together with smaller dials for turbo boost, fuel and water temperature.
Standard equipment included a quartz clock, a leather gear knob, a four-speaker radio cassette player with electric antenna, tinted glass, a tilting glass sunroof and electric heated door mirrors.
Options
To simplify production and keep costs down, the original Sierra Cosworth was offered with a limited choice of optional upgrades. Moreover, Ford gave buyers a choice of just three shades of paint (Black, Diamond White and Moonstone Blue) and one interior colour scheme (grey fabric with black and red patterned inserts).
The original options list for the Sierra Cosworth was limited to central locking and electric windows which were generally fitted as standard to cars destined for the UK. This was also true for the RS500 which meant the only decision a customer had to make was about exterior colour and whether to have the supplying dealer fit the front fog lights which were supplied boxed in the trunk.
Weight / Performance
At 1207kg, the RS500 was 13kg lighter than the base model Sierra Cosworth.
The 0-62mph time dropped from 6.2 to 6 seconds flat.
Top speed rose from 149mph to 153mph.
Production
The 500 cars required for Group A homologation were produced between March and July of 1987.
Of these, 394 were Black, 56 were Diamond White and 52 were Moonstone Blue.
Chassis numbers ranged from WFOEXXGBBEGG38600 to 39099.
Competition History
The RS500 made its competition debut at the 1987 Spa 24 Hour World Touring Car Championship race that took place on August 1st and 2nd. The Eggenberger Sierras locked out the front row in qualifying, but both blew their head gaskets in the race.
In the remaining half dozen rounds of 1987, the RS500s were always on pole and won five times. Eggenberger drivers Klaus Ludwig and Klaus Niedezwiedz would have won the 1987 World Championship, but after a subsequent disqualification from the race at Bathurst 1000 (owing to wheelarch irregularities) BMW’s Roberto Ravaglia was able to claim the title by a solitary point.
After just one season the World Touring Car Championship was abandoned. The European series continued for another year (and was won by BMW) but thereafter, the major Touring Car championships were all domestic contests.
Among the RS500’s most significant titles were those claimed in Britain (1990), Japan (1988 and 1989), Germany (1988) and Australia (1988 and 1989).
Text copyright: Supercar Nostalgia
Photo copyright: Ford - https://www.ford.com
