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Discussion Starter · #1 ·
Imprezas - the 555 cars from 1993, '94 and '95

1993 – Subaru Impreza 555
The production Impreza was launched in 1993, quickly followed by a Prodrive-designed rally version named the Impreza 555. This Impreza assumed the Legacy’s mantle as Subaru’s Group A rallying challenger after the latter’s maiden win on Rally New Zealand in August of that year. Fewer than two weeks later, the Subaru 555 team arrived in Finland with a brand new car, totally different in appearance to the Legacy with which Subaru caught the rallying bug on a global scale.

The Impreza 555 made its World Championship debut on Finland’s 1000 Lakes Rally at the end of August with an entry of two cars, driven by Markku Alen and Ari Vatanen. Vatanen dominated the event, and gave a thrilling demonstration of the car’s potential and a glimpse of what was to come from rallying’s relative new boys. A windscreen de-misting problem ultimately denied the team a maiden victory, but Ari’s second place firmly established the car as one to watch.

Mechanically the Impreza and the outgoing Legacy were very similar. The Impreza retained the Legacy’s compact, lightweight and trademark boxer engine, advanced symmetrical four-wheel drive and strut-type suspension all round but it was made smaller and more manoeuvrable. The small body reduced the overall weight by approximately 15kg, whilst the new turbo, intercooler and cylinder heads produced an additional 15-20 horsepower. It was designed to be rallied from the start: as early as 1990 at the design stage Prodrive was invited to suggest ideas to make the car more suitable for the stages.

Ari Vatanen and Bruno Berglund, RAC Rally, GB, 1993Ari Vatanen and Bruno Berglund, RAC Rally, GB, 1993

1994 – Subaru Impreza 555
Using the same air-to-air intercooler developed for the 1993 Impreza 555 as opposed the traditional and problematic water-to-air item used in the Subaru Legacy, the team eliminated a raft of early reliability troubles and started to rack up results.

With Colin McRae and double world champion Carlos Sainz on board, a third place, second place and the inevitable maiden victory soon followed on the Acropolis Rally, continuing the early promise the car showed in its five rallies the previous year.

More asphalt testing was conducted in 1994, and additionally the intercooler water spray system that caused the windscreen misting on its debut was well and truly resolved. The front differential was also changed to a hydraulic item, as opposed the mechanical setup used by its predecessor. This was adjustable by the driver from within the cockpit and gave the system far greater capability to adapt to surface conditions, with a direct link to the similarly-operated centre differential, for maximum traction and steering response.

Prodrive pioneered much of the work in closed-loop, automated driver systems and 1994 was no different. Mimicking development of the differentials, work continued on the automated gearchange system which used an early form of steering-wheel mounted paddles. It enabled the driver to keep their hands on the wheel when changing gear, but as it was in the early days of its development, the standard manual gearshift level was retained.

Colin McRae and Derek Ringer wow the crowds on Rally Sanremo - D'Italia, 1994

1995 – Subaru Impreza 555
The 1995 season began with a change to the regulations. To restrain vehicle power the diameter of the turbo’s air restrictor was reduced to 34mm. To counteract the substantial reduction in power, the Subaru engine underwent significant development.

With a new camshaft design, compression ratios and a revised engine map, the modifications worked and Subaru’s boxer engine retained a similar level of performance as pre-regulation change. Prodrive’s work was rewarded when Carlos Sainz took victory on the season opener in Monte Carlo.

For the first time a triple-plate clutch was employed in the Impreza, beefing up the twin-plate item used previously. Owing to the regulation changes, longer and wider gear ratios were used in the gearbox and differentials alike to make more efficient use of power throughout the engine’s rev range.

In an era in which rules were being refined and were more open to differences in interpretation between teams, Portugal provided a great example. With no clarification of minimum running weight, Prodrive took a calculated risk with the Impreza 555 of Carlos Sainz, based on their studious and sporting interpretation of the rules. The Spaniard’s car ran without now-essentials such as a spare wheel to win the event, weighing some 60kg lighter than his competitors at the finish.

Work continued in developing the automated gearshift system, still retaining the manual shift lever, and water injection was back for Corsica, providing up to an additional 10 horsepower in the French heat.

Carlos Sainz in action at Rallye Catalunya 1995

1,447 Posts
Discussion Starter · #2 ·
Impreza '96 , '97 , '98

1996 – Subaru Impreza 555
Development on the Championship-winning car of the previous year was limited as efforts and resource were focused on next year’s World Rally car, however Prodrive were still active in extracting every last drop of performance.

On all but the Safari rally, the previously hydraulic front and centre differentials were replaced with active units. These were more efficient at adapting to variations in available traction and, with updated engine management systems, could be preset for specific conditions or driver preference.

Regulations mandated that the minimum weight for all Group A cars was increased by 30kg to 1230kg. Turbocharger housings were more closely scrutinised after discrepancies the previous year, and it was mandated that on the majority of events top-seeded drivers could only carry one spare wheel.

The Impreza 555 used the traditional water injection system for the first time on a cold rally in Sweden, and on Rally Finland in the latter half of the year, the injector nozzle was repositioned to try and optimise efficiency. The boxer engine remained the same but was able to produce the same level of torque but at 1000 revs fewer, making it far more tractable.

The gearbox was also replaced with an Xtrac-built six-speed unit, whereas previously they were Prodrive-built. With the specific and unique demands of the Safari rally, longer gearbox ratios were used to boost top speed and suspension dampers with remote reservoirs were used to cope with the punishing terrain and impacts.

Kenneth Eriksson's Impreza in Service Argentina 1996

1997 – Subaru Impreza WRC97
From 1997 there was a new look to the specifications of cars competing in the World Rally Championship. A new breed of cars was created to the new ‘WRC’ specification. Revised regulations permitted major changes, chiefly to the width of the car, suspension geometry, engine internals and to aerodynamics.

The 555 Subaru World Rally Team were the first to test and launch a World Rally Car in the shape of the Impreza WRC97. The engine in the latest variant was placed further back for more central weight distribution, for many rallies the track width was increased to boost stability, although on certain gravel rallies the narrower track actually worked better as it allowed the car to fit into the ruts left by other competitors.

Based heavily on the superseded Group A Impreza, the WRC97 is perhaps the most iconic of all time, setting the visual standard by which other entries were judged. Renowned auto stylist Peter Stevens was brought in to extract the most from the new aerodynamic opportunities.

The car remained the same length but grew 80mm wider and the bodyshell sat 15mm lower in an effort to reduce the centre of gravity. The compression ratio of the boxer flat four engine was increased, and changes to the manifold and radiator lead to the production of the regulation-maximum 300 horsepower at 1000 revs fewer than previously. Torque was also slightly increased.

The brake discs were enlarged to cope with the generally higher speeds, by 6mm in gravel form and 13mm in asphalt trim. Interestingly the rear asphalt brake discs were actually reduced by 45mm, making them the same size as gravel rears, in an effort to shift brake bias.

Performance development work continued on dampers under the freer regulations, and remote reservoirs were commonly used on all rallies to tackle the issue of fluid heat build-up. As other shifted to sequential gearboxes, the Impreza WRC97 returned to Prodrive-built gearboxes and was the only car to use their pioneering H-pattern layout.

In-car with Colin McRae and Nicky Grist, Portugal Rally 1997

1998 – Subaru Impreza WRC98
The Impreza WRC98 was the only car in the WRC to be newly homologated for the 1998 season, and whilst it looked the same, it featured many new developments to further refine the Impreza such as a revised differential layout and further engine tweaks.

One of the more substantial changes was the shift to a fully active differential setup, replacing the mechanical rear differential used in 1997 with an active item. The front, centre and rear differentials were all active in an effort to increase overall traction. This setup was debuted in New Zealand at the end of July. Following this, there were further developments with the differential cockpit controls to allow the driver to take advantage of their greater flexibility.

Suspension work continued and the WRC98 demonstrated revised suspension top mounts and strengthened shock absorber casings. Suspension setups became increasingly more complex during this era with the employment of closed loop active adjustment systems.

Whilst engine power output remained unchanged, the boxer benefited from a new turbocharger, revised crankshaft and other internal components. It was largely the brevity of these changes that warranted a new homologation for Subaru.

There were plans to install a Prodrive-built sequential gearbox for the first time, but these were scrapped in favour of retaining the traditional H-pattern item, albeit a further revised and refined version.

Colin McRae and Nicky Grist in action, Rally GB 1998


1,447 Posts
Discussion Starter · #3 ·
In the late 1990s and into the turn of the millennium, the technology being used in rally cars was running rife and the Impreza employed the very latest gadgetry to take Richard Burns to the 2001 WRC title.

1999 – Subaru Impreza WRC99
The WRC99 didn’t necessitate a new homologation but under the skin was very different to its predecessor. With the age of technology rife, this was a very cutting-edge car and most of the development work reflected this, focussing on the interaction and endlessly adjustable parameters of the automatically controlled systems in use.

The semi-automatic H-pattern gearbox came into its own this year. While it had been used in one form or other since 1994, this was the first year in which the standard manual gear lever was removed from the car. Instead, the driver changed car by pushing or pulling a paddle behind the steering wheel, and a complex series or hydraulic actuators and electronics changed gear.

This system changed gear faster and with better precision, not only reducing time off the throttle between gear changes but aided the lifespan of the gear ratios with smoother changes.

The Impreza WRC99 also incorporated a fly-by-wire throttle for the first time, pioneered by Subaru and Prodrive. This meant that there was no throttle cable or linkage to the pedal, but that it was all electronically controlled. Demonstrating the complexities of interrelated systems, this was tied to the gearshift systems to allow the driver to change gear without lifting his foot from the pedal. The electronics ensured engine revs were cut accordingly and then matched with wheel speed once the next gear had been selected.

The car also benefited from a new turbocharger, and a lighter and stiffer rollcage to reduce the centre of gravity. On the notoriously tough-on-brakes Rally Catalunya, six-pot water-cooled brake calipers were used.

Juha Kankkunen and Juha Repo take to the air, Rally GB 1999

2000 – Subaru Impreza WRC2000
Subaru started the 2000 season using the Impreza WRC99 for the first three rounds. On its final swansong on the Safari rally it claimed victory, before being replaced for Portugal by the all-new Impreza WRC2000.

The last of the classic shape Imprezas, it drew upon the knowledge amassed by Subaru and Prodrive since the early days of the Legacy and was a complete redesign, as opposed the incremental developments that had gone before it.

Every component on the rally car was examined for possible improvement and although the end product looked similar in external appearance to the WRC99, underneath that familiar skin around 80 percent of the car was new.

Led by designer Christian Loriaux, fundamental changes were implemented to increase stiffness. The rollcage was joined directly to the suspension points for maximum strength, and it was the first time that a team had used the rear differential as an integral part of the rear suspension.

Changes in the engine bay were also fundamental: the huge vents in the bonnet were used to vent the hot air immediately away from the radiator, hence shielding the rest of the engine bay from excess heat. The air intake was also insulated and made more direct to improve air flow. Centre of gravity again ruled supreme: the pedal box was the only item of its kind in the WRC to be floor mounted, to keep the pedal pivots closer to the floor, and even the turbocharger was lowered by 10mm for this end.

Richard Burns and Robert Reid in action infront of hundreds of fans, Rallye Catalunya 2000

2001 – Subaru Impreza WRC2001
In contrast to the incremental body-styling changes of recent years, the WRC2001 represented a significant visual change for Subaru, not least the return to a four door platform that resulted from the parallel development of the road and rally variants.

The proven rally-winning mechanical development that had gone into the WRC2000 was transferred to the new variant, and even more emphasis was placed on aerodynamics, bodyshell strength and weight distribution. Peter Stevens, the guru behind the WRC97, was again responsible for the external elements of the car.

The four-door bodyshell, which shared an intentional striking similarity to the STi roadcar launched that year, was an impressive 250 per cent stiffer than its predecessor, made so by marked improvements in materials technology. The four-door car also allowed greater flexibility with the location of the fuel cell and of various ancillary components to further improve performance.

With the radical new styling, Stevens’ brief was to ensure maximised airflow to the engine bay and intake manifold. The team experimented with air intakes throughout the year, sometimes opting for the bonnet-mounted air scoop and at other times taking air from behind the headlamps at the front of the car.

As the technology behind them improved their effectiveness, the brake discs front and rear were made smaller to reduce the un-sprung weight at each corner of the car. Under new regulations introduced for the start of the year, forged wheels were banned forcing teams to opt for heavier cast items.

The cockpit controls also started to move towards the centre of the car and into a console between the front seats.

Richard Burns and Robert Reid in action, Corsica Rally 2001


1,447 Posts
Discussion Starter · #4 ·
In 2003 the Subaru Impreza World Rally Car was given a makeover, replacing the critically-acclaimed 'bugeye' shape with the fresh 'blobeye', and with it Petter Solberg grasped the World Championship crown.

2002 – Subaru Impreza WRC2002
As with the previous model, the WRC2002 was launched part-way into the 2002 season, on the third round in Corsica. Changes focused on a revised turbocharger housing in accordance with regulations changes, and revised flywheel, exhaust manifold and water injection system.

The net result of the manifold change, contributed to by the new water injection system and turbo housing, was that torque was boosted considerably whilst power stayed capped at the FIA-mandated 300 horsepower.

Once again, work surrounding the water injection system and reservoir was aimed at saving weight, although the 1230kg minimum still applied. Cockpit ventilation was also an area of particular attention, and a revised roof scoop and air ducting were developed. On the dustier events such as Greece, this was so effective it was blanked off to prevent excessive sand and dust entering the car.

Throughout the year general developments (thereby being homologation-free) were made to areas such as the drive shafts, gearbox shift system, and steering column, where the aim was increased rigidity in the latter for improved steering feel.

Due to another change in the regulations, Prodrive reduced the hydraulic pressure in the gearshift mechanism and re-optimised its operation accordingly. The FIA also mandated for the first time that external door mirrors must be mounted on both sides of a car, although this did not affect Subaru due to the similarities of the rally cars to their road-going counterparts.

Tommi Makinen and Kaj Lindstrom on maximum attack, Rally Argentina 2002

2003 – Subaru Impreza WRC2003
The 2003 season saw Subaru launch another new-look Impreza, marked by a more visible focus on aerodynamic aspects of the body and a re-styled front end, most identifiable by the change of headlamp shape.

The new car was launched at the beginning of the season in Monte Carlo, and continued the trend of being a four-door saloon, sharing a parallel development programme with its road-going counterpart. It boasted revisions to the engine, roll-cage, body panels and overall aerodynamic package.

With a new turbocharger and improved exhaust manifold, the torque produced by the boxer engine climbed again. Enhanced engine settings were used from Germany in July to improve performance. Sachs dampers were used, and on Rally Sanremo the team experimented with a form of active suspension on Solberg’s car.

Aerodynamics played a big part, and the new rear wing with its carefully sculpted vertical vanes were an example of design details that were evolved and perfected through advanced simulation programmes rather than the traditional method of testing. Continuing the trend, the cockpit buttons and switches had nearly all been moved to a centre console on the WRC2003, providing fewer distractions in the driver’s immediate line of sight.

Prodrive’s technical expertise meant that the car was capable of being fully equipped and rally-ready whilst running below the minimum weight limit. This meant that the lower components were over-engineered to increase weight and strength, thereby putting more weight lower down and reducing the car’s centre of gravity.

A new FIA regulation also mandated that all WRC bodyshells needed to weigh a minimum of 320kg, as a supplement to existing weight limits.

Petter Solberg and Phil Mills celebrate on the podium with the team, Cyprus Rally 2003

2004 – Subaru Impreza WRC2004
The team started 2004 with last year’s Impreza WRC2003, although sporting a revised ECU, and the new car was launched on Rally Mexico in March. The new variant looked largely the same but, as ever, the changes were concentrated under the skin and in materials used.

The developed ECU used at the start of the season was carried across into the Impreza WRC2004 and was coupled with revised engine internals and a modified cooling system. As anticipated, the average temperature of rallies during the season was higher than previously experienced, so the radiator and intercooler were reclined at the front end of the car to maximise airflow and cooling efficiency.

In a period in which the technical regulations were changing quite rapidly, the team made the most of development opportunities within the rules, but the car was inevitably an interim design solution at a time of turbulence and uncertainty. Until rules became clear, the WRC was in a relative state of flux.

Taking advantage of the bodyshell weight ruling from the previous year, the team fitted lightweight body panels and polycarbonate windows to reduce the shell close to the 320kg minimum. This also allowed them to shed weight from high up on the car and add ballast low down, always working towards lowering the centre of gravity.

Following the early use of water-cooled front brake calipers, the team fitted Solberg’s car with a total-loss water spray system which reduced the temperature of the front brakes by spraying the discs.

Petter Solberg and Phil Mills in action during leg three, Neste Rally Finland 2004


1,447 Posts
Discussion Starter · #5 ·
The final four-doors - the 2005 to 2007 Imprezas
25 September 2008

Bringing us up to date with all but the current WRC2008, our final instalment explores the Impreza World Rally Car of the last three years, from 2005 to last year, including the last of the traditional four doors launched in 2006.

2005 – Subaru Impreza WRC2005
The Impreza WRC2005 was the last in the line of the so-called ‘blob-eye’ Imprezas and had been subject only to incremental changes. The car looked the same as the previous year’s, although in the true spirit of continual innovation to stay at the forefront of World Rallying, the outer appearance hid many developments.

For a start, the bodyshell was made 30mm wider to take advantage of revised FIA regulations. This meant that the car was able to run a wider suspension track and therefore, as the theory demonstrated, be more stable.

The concept of the gearbox remained the same as Subaru had always used: a semi-automatic six-speed unit laid out in an H-pattern, but for 2005 Prodrive worked alongside Xtrac to produce the unit. It remained the only H-pattern gearbox in the WRC.

Suspension components such as dampers and hubs were modified to increase the rigidity of the car with its increased track width, but thought was also given to enabling the camber to be adjusted more quickly. Four stud hubs were used as opposed to the traditional five and a change was made to BBS wheels.

Further changes to the turbocharger, and water and fuel injection systems followed, and a new radiator was introduced that comprised individual heat exchangers to aid cooling. Components were lightened where possible, including the front and rear bumpers which were produced from composite material rather than metal for the first time.

The total-loss water spray system to cool the front brakes that was tested at the end of 2004 was fitted from the start of the season.

Petter Solberg in action on SS12 during leg two, Telstra Rally Australia 2005

2006 – Subaru Impreza WRC2006
In 2006 Subaru launched a newly-styled Impreza amid a number of changes to the WRC regulations. The largest change was that active front and rear differentials, as used since 1998, were banned and the team reverted to a hydraulic setup front and rear. The centre differential was permitted to remain active, and it was made much more responsive and controllable.

Systems used in one way or another since the Impreza was born, water spray to the intercooler and water injection were both banned. This was overcome with developments in fuel management improvements and internal friction reduction, and immediately the 2006 boxer engine was more powerful. Developments in the Prodrive-built gearbox reduced the gearshift time by half.

It was also mandated that engines and components had to last longer, giving rise to engine pairing of events, and the use of spare parts was restricted by a method of FIA sealing and record-keeping.

Safety also became more of an issue for the start of the year and changes to seats, belts and rollcages made the cars safer for driver and co-driver and more resilient to impacts. The revised rollcage bars were also designed to hold the spare wheel more centrally in the car to aid weight distribution.

The impact of the regulations and safety measures meant that all teams had to introduce their new cars at the very start of the season in Monte Carlo so as to be eligible, as 2005 WRC cars didn’t stand up to the fundamental rule changes.

Stéphane Sarrazin in action on SS12 during leg three, Tour de Corse 2006

2007 – Subaru Impreza WRC2007
As per previous years, the Subaru World Rally Team started the 2007 season with the Impreza WRC2006. The updated version, more a facelift model than a new car, was launched on Rally Mexico at the beginning of March.

Designed to be an interim iteration before the launch of the completely new WRC2008, it nevertheless demonstrated many key developments. Sporting a revised intercooler and re-routed radiator, the air intake was via the iconic and stereotypically-Subaru bonnet scoop for the first time in recent years. The bonnet vents were also revised, leaving two hot-air escapes at either side and losing the central vent.

The Impreza WRC2007 continued to use passive front and rear differentials under the regulations imposed for 2006, with the centre still active. The team signed a commitment to new suspension damper supplier BOS, and all WRC cars adopted BFGoodrich tyres for the season.

The spare wheel was moved from the boot into the cockpit of the car, where it was further away from the heat of the exhaust and more accessible to the drivers. This meant that the exhaust exited through the rear bumper for the first time, rather than beneath it.

Transmission work was focused upon more efficient use of the centre differential to maximise traction. Weight saving here and within the engine helped optimise weight distribution, whilst setup changes with the new dampers focused on efficiency of tyre usage.

It is the last of the traditional saloon-shaped Imprezas, marking for some the end of an era and the very exciting start of another, hailed by the Impreza WRC2008.

Chris Atkinson in action on SS18 during leg three, Rally Mexico 2007

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