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