The Final Four-Doors – The 2005 to 2007 Imprezas

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.

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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.

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.

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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.

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.

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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.

comparisons of the wrc 2005 to 2007. now i can see those differences better.. from HSPN.

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