Latest Impreza set for Mexico debut.

The very latest evolution of the Subaru Impreza World Rally Car, the WRC2004, will make its competitive debut on the Corona Rally Mexico, which begins from the town of Leon on 11 March.

Taking full advantage of the latest FIA technical regulations, and incorporating a host of improvements in such areas as the bodyshell, engine, suspension, electronics systems and aerodynamics, the WRC2004 is the latest development of a car that has earned a formidable reputation on rallies around the world with 38 WRC wins since it burst onto the world rally scene back in 1993.

Born of Subaru's desire to harness the engineering skills of its teams at Subaru Tecnica International [STI] and Fuji Heavy Industries Ltd [FHI] - the manufacturer of the Subaru range - in Japan and at the Subaru World Rally Team's base in the UK, the WRC2004 is the result of a 14-month design and development project that has involved the three parties working more closely than ever before.

Following the introduction last year of the WRC2003, with its new aerodynamic package, aggressively styled front end and unique sectioned rear wing, the brief for the WRC2004 was to develop other areas of the vehicle, notably those under the skin.

"If you look at the development process of the Impreza over the last ten years, there's a consistent three-year cycle," explained Subaru World Rally team principal David Lapworth, "Typically, about a third of the car is new with each evolution. The 2003 car was the first phase of the current Impreza model. Last year, we made a lot of progress in areas like aerodynamics and suspension systems. For this year, although there have been further revisions to the aero package and suspension, the focus was on the engine, electronics systems and the bodyshell."

Presented in the familiar blue-and-yellow Subaru World Rally Team colour scheme, the casual observer could be forgiven for thinking that little has changed from the previous WRC2003 version but, under its familiar bodywork, the WRC2004 is packed with the very latest technology and is a very different animal indeed.

Work on the car began in January 2003, and was overseen by Ed Wood, the team's new chief designer. With a first class reputation as a research and design engineer in Formula One, Wood was responsible for ensuring that the project made the best use of the latest technological developments, as well as the wealth of experience learned over more than a decade of WRC competition.

"More computer aided engineering techniques were used to design the WRC2004 than on any of its predecessors," he said, "The team has made a big investment in the adoption of Finite Element Analysis [FEA] techniques here in the UK and at STI in Japan, and wherever possible we made use of these modelling and simulation facilities to assist our work.

"This, combined with the close working relationship we have with our colleagues in Japan, has allowed us to be very agile and had a significant impact on the speed at which we are able to undertake development work. We were able to react and implement new solutions very quickly. In fact, by mid April, evaluation testing on some of the of the 2004 car's sub-systems like brakes, transmission and suspension was already underway."

Bodyshell changes were next on the agenda - specifically, making the best use of new FIA technical regulations that permit the inclusion of lightweight bodywork components.

"We've fitted polycarbonate rear and side windows, which weigh about half as much as their glass equivalents, and have replaced the steel front wings and boot-lid with lightweight aluminium components which were provided by FHI," Wood revealed, "Really, this sort of work is just what you'd expect us to do when faced with the new technical freedoms, and we're certainly not the only team to be working with these types of lightweight materials.

"For me, it's the other modifications we've made to the shell that have been more satisfying from an engineering point of view. We've made considerable changes with the aim of achieving greater overall structural efficiency - a stronger shell with less mass. The end result gives a significant increase in overall stiffness as well as a favourable centre of gravity."

While the majority of bodyshell changes are only visible from inside the cockpit, further refinements have been made to the external aerodynamic package with the emphasis on maintaining an effective airflow for cooling without increasing drag. The attention to detail shown by the project team has seen the mounting angle of the engine radiator changed to assist airflow, while the ducted system that vents hot air from the turbo intercooler through a slot in the bonnet remains. The innovative rear spoiler, designed to maintain yaw stability at high slip angles, has been further refined. The result is that, when compared to the WRC2003, the new car's cooling and aerodynamic processes are far more efficient.

The Impreza's trademark flat-four, horizontally opposed 'boxer' engine is now more powerful than ever before. Developed in tandem with STI's engine engineers in Japan, enhancements were made to the IHI turbo charger, exhaust manifold and fuel injection system, as well as key internal components like the crankshaft, pistons and camshafts.

"In working on the engine, we made full use of the dyno testing and simulation facilities here and at STI," Wood explained, "The net result is an engine that gives a wider spread of useable power and torque that provides improved response and drivability."

Making full use of the latest vehicle dynamics simulation systems, the suspension of the new car has also undergone a process of refinement. Building on the successful introduction of new dampers in 2003 and set-up lessons learned throughout the year, the WRC2004 features a more consolidated package that allows adjustment in all key areas.

There have also been modifications made to the electronics systems on board. A new wiring harness has been developed alongside an integrated control system, that replaces the previous separate chassis, engine and transmission ECU's. Originally introduced on Petter Solberg's San Remo car, and run on his car for comparative purposes for the rest of the season, the software - which again was designed in collaboration with STI - provides enhanced control in many areas. With less duplication of sensors, faster processing speeds, more data logging memory and easier manipulation of data, the integrated system enables engineers to get the very best out of the crucial dynamic elements of the car.

Testing of the WRC2004 began last November and, with the forthcoming event schedule, has been predominantly focussed on loose surface work. Having driven thousands of kilometres on test roads with the new car, feedback from Solberg and new team-mate Mikko Hirvonen has been very encouraging, with both commenting on the improved drivability and performance.

With the first competitive test of the new car less than three weeks away, Wood is full of praise for the close-knit group of engineers at Subaru who have ensured the smooth running of the project.

"Overall, I think the new car is a tribute to the way our team works by drawing on the experiences gained over the past eleven seasons, as well as being open to new techniques from other areas of motorsport," he said, "The joy is that in our engineering team we've got a group of individuals who are deeply passionate about rally and technology, but who are able to contribute engineering solutions from a broad range of different backgrounds - not just other rally cars, but road cars and Formula One.

"For me, the beauty of designing a rally car is that it is the broadest canvas to work on in terms of motorsport - it has to be good in so many different conditions, that the end result is something pretty special."