When a car is already the fastest machine in the world championship, as shown by the number of fastest times Petter Solberg single handedly made during the 2004 season with the 2004 Impreza, is it possible to bring out a newer and better version?
One year on since the 2004 model was introduced in Mexico, Subaru’s 2005 version Impreza World Rally Car made its debut, again on the third round of the series. On this model there are no completely new design philosophies, but a lot of attention benefiting from continued experience in competition.
Areas in which the car has been improved can be categorised as follows:
a) The main change is the widening of the car, taking advantage of the rule permitting bigger World Rally Cars (those with overall length exceeding 4200mm) to be widened from 1770mm to 1800mm, thereby allowing wider suspension tracks to be fitted.
Wider tracks help the handling by lessening the effect of weight transfer by proportionally making the car lower than before. Various changes have been made to widen the track including new uprights and suspension arms, and computer design techniques have enabled greater attention to be paid to calculating the correct weight/stiffness ratios for components.
Further, changes to the strut mountings allow for faster camber adjustment. The front and rear fenders have been made out of composite rather than metal, to reduce weight.
b) Engine development.
There are detailed changes to the IHI turbocharger design, new water and fuel injection systems, a lighter flywheel and many lighter components. Work on the injection systems has focused on ensuring the correct quantities of fluids are supplied to individual cylinders.
There are now four separate water injectors, one for each cylinder, mounted on parallel rails.
c) More benefit has been gained from wind tunnel work, especially in the under bonnet layout of the radiator, to gain improved internal air flow, particularly in the light of problems experienced when passing through water crossings in Turkey and Argentina.
Noticeable at first glance is the revised shape of the lower front aperture, now in the form of a flat rectangular opening. Roof vents are optional depending on climatic conditions.
The water radiator mounted under the intercooler is again sharply angled backward, and has a system of terraced heat exchangers mounted on the radiator itself. This was a system which the team tried out last year after Cyprus.
d) Transmissions have been improved with a revised hydraulic system, but are otherwise unchanged.
e) In the cockpit, electronic systems have been repackaged and the central console made more systematic for easier servicing. The pedal box is floor mounted, with the necessary hydraulics under the floor.
Testing has been carried out over the past months with the final work in Sardinia in the hands of Petter Solberg, Chris Atkinson and resident test driver Pasi Hagstrom. Reports from drivers speak about noticeably improved balance of the car and improved traction.
The engine gives the feeling of better torque and throttle response.
There have been some changes of suppliers with the introduction of this model, notably BBS wheels, while Sparco has supplied a range of accessories. The team continues with Sachs dampers and AP brakes.
Development of this model was, like on the previous examples, a joint exercise between the parent company Fuji Heavy Industries in Japan and the Subaru World Rally Team operation based at Prodrive in Britain.
The object is to bring further together the development of road cars based on the experiences gained from competition.
This also allows the styling of future road cars to benefit from the images created by competition versions. Japanese stylist consultants have helped in shaping the new car.
Areas in which their work has focused are the front and rear wheel arches and the front and rear bumpers. Engine development work has also been a joint operation between Japan and Britain.
In its 12 month lifespan as a works rally car, the 2004 model won six rounds of the championship, all in the hands of Solberg and brought the Norwegian driver into second place in the Drivers’ series.
And at the end of the 11th year in the life of the Impreza World Rally Car in the championship, it has proved to be the most successful model of all, winning both the Manufacturers’ and the Drivers’ series three times each.
Petter Solberg celebrates his Rally Mexico win in 2005.
- Photos: Martin Holmes, Maurice Selden
Solberg's second win in the car was on the 2005 Rally of Great Britain.
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