Project approved on June 1 1998, design concept finalised a month later, the 2-litre turbocharged four-wheel drive Citroën Xsara rally car first tested on April 16th 1999. Its first World Championship rally was the 2001 Catalonia Rally: just over one month shy of two years since its first test.

Initially Citroën did not sanction the Xsara WRC to contest the World Rally Championship. The first Board authorisation was to contest the 2000 French Rally Championship while homologated in a special national category: 'France Rally Car', created by the FFSA to enable the car, named Xsara T4 at the time, to dominate that series. Then in the same year came approval for the car, homologated as Xsara WRC, to build towards full World Rally Championship attack in 2003 from a 25% involvement in 2001 and 50% in 2002.

The Xsara WRC was homologated for motor sport by the FIA on the 1st March this year. Variant options were incorporated for the rollbar, transmission, suspension, running gear, windows and bodywork, the latter reflecting that the road Xsara underwent a facelift [from production model designation N6 to N7] in late 2000.

The transformation from N6 to N7 was lengthy, involving the bonnet and bumpers and fenders front and rear, and 100% verification of the detail design of each component in the car. Maximum WRCar width is 1770mm, and so Citroën Sport had the opportunity, as with the N6-based T4 Xsara, to engineer front and rear fenders to take the car to that maximum.

It was not possible to base this work on the outgoing N6 bodyshell, as revisions were introduced to the front of the N7 road car to suit later crash regulations. The N7 'shell is a few kg heavier than the N6, but not an important quantity.

The work involved starting again in the wind tunnel, firstly with a quarter scale model, then 1:1 scale, to optimise aerodynamic characteristics. Also included was work to improve underbonnet airflow, both to improve engine cooling and reduce in-car temperature. The Xsara's turbocharger and exhaust are at the rear of the engine, just in front of the crew, increasing heat radiation compared to cars with turbo and exhaust in front of the engine. However, the arrangement of the Citroën's aspiration equipment does help bring mass rearwards.

Suspension
During its asphalt world rally outings this year, the Xsara WRC has exhibited impressively low levels of tyre attrition and equal wear. It is the same for the gravel specification, and one can surmise that the Xsara WRC's evidently extensive [yet not disclosed] wheel travel derives from the many years of experience the team had when winning 36 out of 42 rally-raids contested with the ZX Rallye Raid between 1990 and 1997.

Jean-Claude Vaucard, the car's chassis engineer, explains the philosophy which has achieved this: "You need the best in all cases: a good competition car is a car with everything; every detail, everything: and you make the total of all these small things. So you cannot say it is a compromise between that and that; if you can make no compromise, better to work on each point."

Citroën Sport works closely with Extrem Tech on damper design. Having been the chassis engineer responsible for the twice consecutive World Champion rally car [in 1985 and '86], the Peugeot 205 turbo 16, then the engineer responsible for the devastatingly effective rally-raid derivatives of that 'T16' concept as both Peugeots and Citroëns, Jean-Claude Vaucard is a rally car suspension expert.

Citroën Sport's impressive new 25,000m2 Versailles facility contains the - long stroke - damper rig the team used to test rally-raid dampers. For security its base is buried six metres in the ground. WRCar dampers, having less stroke, run at higher speeds than those on rally-raid cars, with damper speeds on gravel approaching four to five metres per second.

Citroën Sport has modelled an externally controlled reactive suspension system, but Vaucard explains: "You cannot go every way, so actually we don't choose to work in this direction [but] I think it can be something to improve for sure."

Transmission
At 4167mm long, with a wheelbase of 2555mm the Xsara WRC is a good compromise size for a World Rally Car: "Not too long; not too short," explains Jean-Claude Vaucard, with the proviso: "But in some twisty roads it is an advantage to have a very short car, and now it is easier to make the car stable in high speed when the car is small. With the inertia in a small curve, if you have a long car you can do nothing, but I think it is easier for a small car to be stable in high speed than to have a long car manoeuvrable in a small corner."

The Xsara boasts sufficient available internal space for Vaucard to be free to decide on its transmission orientation. He calculates no large differences between transverse and longitudinal gearboxes, but finds no convincing weight distribution advantage in the longitudinal arrangement used by Ford, Peugeot and Hyundai, concluding that the latter carries an extra 20kg minimum penalty, which can be used help move the car's centre of gravity more to its rear.

Additionally, in transferring torque via an extra drop gear set, the [pull-type] clutch, plus bevel gears to turn the drive through 90 degrees: at a nominal efficiency loss of about one percent per gear stage the longitudinal transmission set-up soaks up more torque than an 'in-line' gearbox. Vaucard calculates the longitudinal difference in a car¹s centre of gravity position resulting from the use of a longitudinal gearbox at around a maximum of two inches, because most of the heavy parts in that gearbox are towards the front.

With a transverse engine in the right-hand side of the engine compartment another disadvantage of the longitudinal transmission in Vaucard's view is a loss of weight over the front, left, wheel. And so the Xsara WRC's gearbox is transversely arranged, containing a derivative of the Xtrac gearbox cassette which first appeared in the Xsara Kit Car. To decrease torque inside the gearbox, Citroën Sport has arranged for the shafts in the WRC 'box to rotate faster relative to crankshaft speed.

The latest transmission development is an electro-hydraulic automated gearshift which appeared at Rallye Deutschland last July. This requires modifications at the gearbox to replace the cable control of the sequential barrel with linear hydraulic actuators.

While dominating Deutschland in the Xsara WRC, Philippe Bugalski experienced some difficulties with the semi-automatic shift. Vaucard: "It is incredible - we made a lot of tests: zero problem, and when we came to the rally we discovered some functional problems, but we didn't discover them in tests because the drivers don't drive in the same manner." The main problem was that software was unable to shift down through the gears sufficiently swiftly into hairpins. A second mechanical problem with a small ball and spring blocked the 'paddle' gearchange lever. "But that's why we wanted to run it in an event as soon as possible before Sanremo and Corsica to have something working properly," explains Vaucard.

Processed electronic information from transmission and engine management computers converts to hydro-mechanical control of the semi-auto shift and the car's front, centre, and rear hydraulic differentials. The latter are of a diameter providing suitable robustness and contain "a lot of discs."

Maximum direct hydraulic pressure of 100 bar controls the frictional/'locking' action provided by these discs, while the semi-auto change takes pressure from an hydraulic accumulator, pressure in both cases being provided by an engine-driven twin-stage pump. Some WRCar teams employ lower pressures for their diffs, but Vaucard reasons: "If you are able to work with high pressure you reduce weight and also inertia and so on - just to be sure that you have no leak problem, and you are able to work at this pressure." Current hydraulic seals are good for maintaining 100 bar, but that is the limit, explains Vaucard.

Electronics
This is the area in which Citroën Sport strives most, with partner Magneti-Marelli, to improve on the Xsara WRC.

Vaucard is convinced there is scope for major improvement in the way the car's 32-bit MR3 engine, and its chassis, electronic control systems function: "We need more possibility, so we are looking to the future to change the system. Normally it is for next year [for a more powerful system]. We are about at the limit of the system with all the electronic systems that we use on the car, for the engine and for the chassis. So now it is good to start the [2001] season like we are, but we have to change as soon as possible."

Engine
The first Citroën Xsara to be homologated into Group A was the two-wheel-drive, normally aspirated 2-litre Kit Car in March 1998. To take advantage of its large valve sizes, this car uses PSA's 2-litre XU10J4RS engine, which has a cast iron cylinder block.

A World Rally Car's 34mm restricted turbocharger means that the smaller valve sizes in the alloy block 1761.7cc XU7JP4 engine are much less a penalty than would be the 20kg extra weight of the 2-litre iron block. So, the 1.8-litre Xsara VTS was homologated into Group A on March 1st last year in order that the four-wheel-drive turbocharged 2-litre Xsara rally car could use the lighter alloy block, bored and stroked to 1998cc, and using a conventional forged steel crankshaft.

With FIA homologation lasting seven years, this means the Xsara WRC can use the XU7JP4 alloy block engine until 2006, in theory. PSA's XU engine series began life in Citroën BX and Peugeot 305 models in 1982, and there is a wealth of competition experience and knowledge of turbocharged derivatives of the XU engine, which have formed the basis of PSA rally car propulsion since 1983. However, the production life of PSA engines is between 20 and 25 years, meaning XU engines will almost certainly not be fitted to PSA production cars by 2003.

A new range of PSA engines has recently appeared, entitled EW. First fitted to the five-door Xsara in August 2000, the 2-litre EW10J4 unit has an alloy cylinder block, and Citroën's replacement production car for the Xsara will be generally available before the end of 2004. It is not unreasonable to expect Citroën Sport at least to investigate the potential in a turbocharged WRC version of the new EW unit.

The most important engine modifications for the 2001 homologation of the XU7JP4 unit in the Xsara WRC were modified impellor, turbine and compressor for the Garrett turbocharger and the inclusion of water injection. These changes improve torque output by a factor of more than 15% and bhp is up by 6%. The 2001 engine has a lighter flywheel, a 7% increase in compression ratio [water injection] and retains its slightly longer stroke-to-bore ratio.

Through 2001 the team has made detail changes to the electronic mapping to suit its boost pressure/anti-lag, or fresh air, system. A new homologation of the car is being prepared for 2002, most likely to be on the 1st March. The engine details of this homologation are not yet finalised, but no major mechanical changes are planned and likely modifications will be mainly in ancillary areas such as inlet and exhaust manifolds, anti-lag system and turbocharger.