History Lessons #25 – Ford Sierra RS Cosworth

Published On October 17, 2013 | By Jared Robinson | History Lessons

Not everyone is a purebred. In fact, if you’re like most of the people on this earth, you come from two separate and distinctive families. The new Ford Focus ST follows a similarly branching family tree. For the first time, the high performance Focus you buy in the US is the same as the one you could buy in the rest of the world. We’ve tasted from the European performance well in the US in the past as recently as the 2002 – 2004 Focus SVT, which was similar to the European Focus ST170. This World Car attitude is very present in the current and upcoming Ford vehicle catalog; the Fiesta has been for sale here for some time now and the Ford Fusion is very much the same as the new Mondeo seen throughout the rest of the world. In this series, we’ll look into the history of compact performance offerings from Ford and how two parallel developments in the US and Europe have evolved into the new Ford Focus ST.

Today we’re going to celebrate one year of Project-ST history lessons with our 25th entry. This one was requested right from the start by seemingly everyone. “When are you going to do one about the Cossie!?” we were asked. The answer has always been easy to deduce: once we get to 1985, of course. Before we dive right into the Cosworth YB powered monster, we need to look at the car it’s based on: the Ford Sierra.


The early Sierras had an actual front grille; fashionable, contemporary women were clearly okay with that.

The Ford Sierra was the successor to the Ford Cortina. You may remember the Cortina from way back when we first started publishing these History Lessons. We saw that the Mk2 Cortina was already getting larger and by the time the Mk5 Cortina was introduced it had graduated in size to a proper family sedan, with the Escort filling the now-vacated compact ranks. The Cortina had an uninterrupted run from 1972 to 1981 as the best-selling car in Britain, losing that title in 1982 to the Escort. Its replacement was the Sierra. Designed by a German, a Frenchman, and Maximum Bob (Lutz), the Sierra was a design ahead of its time. Aerodynamic style was the order of the day for Ford and the Sierra was the pinnacle of that style in 1982. In a major change, the Sierra was not initially available as a sedan and only as three and five door hatchbacks and a wagon. The styling of the Sierra even influenced the design of our own US-market Ford Taurus. The design was initially very polarizing to some people. After years of straight-edged styling people took the Aeroback styling as blob-like and the car was derisively nicknamed the “Jellymold.” Initially, sales were slow as there were many Cortinas still on the lots to sell at major discounts. The reaction to the car was very similar to New Coke, with many spreading rumors that Ford would simply reintroduce the Cortina out of desperation for sales. This proved to be untrue and the styling eventually broke that jellymold, and aged rather well with many buyers.

The XR4i was the initial performance version powered by a 150hp 2.8L V6

The XR4i was the initial performance version powered by a 150hp 2.8L V6. Laser beams also shot out of its tail lights.

Underneath the aero styling was a new independent rear suspension mixed with rack and pinion steering (as opposed to the less direct recirculating ball) providing the ingredients for a proper handling sedan for the time. The engines offered were the Cologne V6 and Pinto fours as well as a Peugeot-sourced 2.3L diesel. These engines were coupled to a four or five-speed manual or a three-speed automatic transmission. The performance model was the XR4i, powered by a 150hp 2.8L fuel-injected V6. The XR4i was different in that it had a unique rear quarter window. This window was bisected, allowing for a pop-out vent window, and was moved farther forward, which reduced the thickness of the B-pillar. Many considered the Sierra to be just another family or fleet car, at least until Cosworth had their way with it.

Cosworth has had its hands in Ford and the RS brand for some time now. Starting with the BDA powered Mk1 Escort RS1600, Cosworth really helped to shape the RS division with its purpose-built motors. Though, with the previous Cosworth-powered RSs (Mk1 Escort RS1600, Capri RS3100, Mk2 Escort RS1800) the Cosworth name never adorned the car itself. This was to change with the Sierra. In 1983 the head of Ford Motorsport of Europe, Stuart Turner, wanted to regain the competitive edge that Ford once held. Turner looked for support from Walter Hayes, the man who pushed the development of the Ford GT40 and Cosworth DFV, and who also helped gain support from the brass at Ford to go ahead with a new RS model. With the VP of Development, Ken Kohrs, in tow, Ford tapped Cosworth again to help. At the time Cosworth had developed a new engine off of the Ford T88 engine block (aka, the Pinto). Fitted with dual overhead camshafts and 16 valves, the prototype engine was dubbed the YAA. Ford put in a request that this engine be turbocharged and capable of at least 180hp in production trim and 300hp in race trim. Cosworth responded by saying that the street trim would produce no less than 204hp and that the order should be for no fewer than 15,000 engines (dubbed YBB). At the time, Turner had no plans to build more than 5000 units of the new car (the required amount for Group A homologation), but accepted the order conditions anyway. This was obviously a rather ambitious project, as Ford would order three times the needed amount of motors and Cosworth would deliver them with 24hp more than requested. What was done with the surplus 10,000 motors is an interesting story that we’ll get to in a later History Lesson.

Behold! The Cosworth YB!

Behold! The Cosworth YB!

With the engine developed, a transmission had to be sourced. Ford turned to Borg-Warner for these duties. The venerable T-5 transmission had been making itself a well-known transmission in the Ford Mustang overseas. The power it was capable of handling was right in line with the YBB motor. The problem ended up being that the higher redline of the YBB caused some minor problems. To handle this, Borg-Warner developed a special T-5 transmission specifically for this new engine. Once the engine and transmission were sorted, it was time to decide on which car it was going into. It was unsurprising to see the Sierra tapped for this duty because it was already rear-wheel-drive and could already fit the Pinto motor. Some changes to the base Sierra needed to be done and those changes came from an unlikely source: America. While we haven’t discussed it yet, the Merkur XR4ti (an American rebadge of a Sierra XR4i powered by a turbo Pinto engine similar to what was powering the Mustang SVO) was running in IMSA under Jack Roush. The development for suspension and aerodynamics on the Merkur were given to Cosworth. Additionally, production bits from the XR4ti like the integral boost gauge and the chassis stiffening plates made it into the Sierra RS Cosworth as well.

The car came in 3 colors: Black, White and Moonstone Blue. Guess which one this is.

The car came in 3 colors: Black, White and Moonstone Blue. This one is neither black nor white.

The somewhat maligned styling of the car worked in its favor when it came to motorsport. While the car had low drag, the hatchback design created a lot of rear lift. The solution: a giant rear wing. The rear wing raised some concerns with Ford but when explained that it was the only way for the car to maintain contact with the road at 180mph, Ford designers agreed to continue with production. Other changes to the body were an actual grille inlet between the lights to feed the intercooler and large fender flares to cover the 10″-wide wheels destined for the race track. Ford met with their dealer network to assess the sales potential of this new car. Dealers didn’t know what to do and assumed they could sell only 1500 of these. Ford didn’t give up and started a campaign to get dealers in the cars to drive them. With a renewed sense of enthusiasm from the dealers after some spirited drives and some measures on Ford’s part to reduce the cost of the car (namely: the choice of only 3 exterior colors, 1 interior color and one option package which included central locking and electric windows), the Sierra RS Cosworth rolled into production.

It was presented to the world at the Geneva Motor Show in March of 1985. Sales began in September of that year with the expectation for final production of the 5000 units to conclude in 1986. By July of 1986, 5545 units were produced (all right-hand-drive) with 500 of them heading off to Tickford for conversion to RS500 status. The RS500 was an even rarer bird. The already Cosworth fettled Sierra was then sent off to Tickford where they received a more robust engine coupled to a larger turbo and intercooler, a secondary fuel injection system with a larger pump, a revised induction system, upgraded cooling system, an additional rear spoiler and a redesigned front bumper with more intakes for cooling. The end result was 222hp from an engine dubbed the YBD.

The 1987 Sierra RS500 Cosworth in it's rare "not stolen" form.

The 1987 Sierra RS500 Cosworth in rare not-yet-stolen form.

The car gained attention straight on. The Sierra RS Cosworth, nicknamed “Cossie” by nearly everyone, became one of the most sought after cars… particularly by thieves. On the street, they were every boy racer’s wet dream: a turbocharged, big rear winged, rear-wheel-drive hoonmobile. Regardless, the street was not the main focus; the car was designed for motorsport and that’s where it excelled. It was immediately entered into the inaugural World Touring Car Championship (WTCC) where it competed against the E30 M3. By August of 1987, the RS500 was homologated and started to be used. At that time, the WTCC was nearly over with only six events remaining. Though with that, Ford took pole in all six events and finished first in five of them. Had it not been for a questionable disqualification at Bathurst, the Cossies would have finished in 1st in the driver’s championship having only placed 2nd by 1 point in the standings. Despite that the Texaco liveried Cossies finished 1st and 4th in the entrants championship. They faced stiff competition from Japan in the following years thanks to the newly introduced all-wheel-drive Nissan Skyline GT-R but continued to compete in many rounds of Touring Car Championships all over the world.

The Texaco Cosworth at Bathurst. It held pole position at the Bathurst 1000 in '87, '88, '89, '90 and '92

The Texaco Cosworth at Bathurst. It held pole position at the Bathurst 1000 in ’87, ’88, ’89, ’90 and ’92.

It’s not an RS unless it goes rallying, and that is just what Ford did with the Sierra RS Cosworth. Introduced after the folding of the Group B formula, the Sierra competed in Group A rallying. It was immediately placed at a disadvantage due to being rear-wheel-drive only. In an attempt to compete, Ford would campaign both a Cosworth and an XR4x4 in Group A. The Cosworth would race on the tarmac events while the XR4x4 would compete in the loose surface events. The lack of power produced by the XR4x4 led the car to be outpaced by the much faster Lancias and Mazdas of the time. Despite that, the two-wheel-drive Cosworths consistently finished in the top five and even won the 1988 Corsica Rally. More and more cars were becoming four-wheel-drive and like its time in Touring Cars, the Cossie was soon outpaced.

Despite being a little late to the party, the Sierra RS Cosworth set the groundwork for two more cars to follow. The updated Sierra Sapphire RS Cosworth and finally the Escort RS Cosworth, which introduced four-wheel-drive to the equation. We’ll discuss them more in future History Lessons.

Interested in buying one? They’re all past the 25 year importation rule but are only available in right-hand-drive (but it’d make a fantastic mail car). Check out this buyer’s guide or buy this book if you’re interested. Converting a Merkur XR4ti is also an option, but tackling the rear windows requires custom Perspex and cutting the XR4i-style window portions out or a regular 3-door Sierra roof to be welded on. You can see some discussion of XR4ti conversions here.

When we return next: mid-engine Group B madness.

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