2007 Subaru Impreza STi WRC2007 review

Subaru Impreza STi WRC2007 review:

As with previous incarnations of the iconic rally car, the Impreza WRC2007 is the result of a close collaboration between the teams of engineers and designers within Fuji Heavy Industries Ltd and Subaru Tecnica International (STI) in Japan and the Subaru World Rally Team in England.

The creation of the WRC2007 is a sign of Subaru’s ongoing commitment to the World Rally Championship as a way of proving the superior performance, reliability and safety of the Impreza model. Although the latest World Rally Car is outwardly similar to its predecessor, a number of key engineering improvements have justified the production of a new car for the remainder of this season.

Steve Farrell, director of engineering for the Subaru World Rally Team, explains: “The targets were to produce a car that has a more responsive front end with better traction and more balanced tyre wear, particularly on longer stages. To achieve that, we have applied a different philosophy into areas such as weight distribution, suspension geometry and differential set-ups. We also have new dampers to improve road-holding and traction.

“The car also has a different radiator and intercooler pack. We made an evolution in the middle of last season and, with the benefit of the new homologation, we’ve been able to make a further step on that. We have simplified the layout, which has improved the air flow, made the front end of the car easier to service and lost some weight.

“Externally, the differences are relatively subtle. The front bumper has been restyled to suit the new radiator pack and the bonnet vents are different – we have twin side exits on the bonnet this time rather than one central one.”

Richard Taylor, Subaru World Rally Team managing director adds: “Since the latter part of last year we’ve worked very closely with Subaru in Japan to look at certain specific areas of the 2006 car and bring the new version to fruition as quickly as possible. This season we have started to work with BFGoodrich and Mexico will be our first gravel event with its tyres, so we still have a considerable amount of learning to do in that respect.”

As the basis of a rally winning machine, few cars can match the competitive pedigree of the Impreza. First launched in 1992, the road car has developed in tandem with its rallying counterpart and over the last 13 seasons, the Impreza has scored 46 WRC victories and lessons learned on the rally stages have been fed back into the production model.

Like the road-going Impreza, at the heart of the rally car are two key parts of the Subaru philosophy, namely the Horizontally-opposed engine and the trademark Symmetrical AWD (All-Wheel-Drive). Through the work of STI and the Subaru World Rally Team, Subaru has established a two-way feedback process which complements both the road and rally car programmes.

Shigeo Sugaya, manufacturer principal, engineering, for the Subaru World Rally Team, says: “The collaboration between Subaru in Japan and England has worked extremely well to deliver the WRC2007 in a very short timeframe. Last autumn, engineers in Japan and England shared the idea before actual work started on both sides. Then development work was initiated as a joint project between the two teams.

“Our engineers in Japan are responsible for two main areas: the first is designing the bodyshell, including aerodynamics, and the other is improving the power unit. The engine itself contributes to further improving drivability in the middle to low speed range, which worked effectively in the Impreza WRC2006. As with previous designs, the engine is an all-aluminium construction, but the further use of light-weight materials means it is even lighter than before.

“On top of that, we work very closely with the Subaru World Rally Team engineers on specific projects and offer general support as and when it is needed. We also set up smaller groups including engineers from both Japan and England to develop areas such as the suspension or aerodynamics. The groups communicate directly, while my role is to oversee the success of each project. The WRC2007 does not represent a radical change for the team, instead we have made small evolutions in several areas.”