Impreza '96 , '97 , '98
1996 – Subaru Impreza 555
Development on the Championship-winning car of the previous year was limited as efforts and resource were focused on next year’s World Rally car, however Prodrive were still active in extracting every last drop of performance.
On all but the Safari rally, the previously hydraulic front and centre differentials were replaced with active units. These were more efficient at adapting to variations in available traction and, with updated engine management systems, could be preset for specific conditions or driver preference.
Regulations mandated that the minimum weight for all Group A cars was increased by 30kg to 1230kg. Turbocharger housings were more closely scrutinised after discrepancies the previous year, and it was mandated that on the majority of events top-seeded drivers could only carry one spare wheel.
The Impreza 555 used the traditional water injection system for the first time on a cold rally in Sweden, and on Rally Finland in the latter half of the year, the injector nozzle was repositioned to try and optimise efficiency. The boxer engine remained the same but was able to produce the same level of torque but at 1000 revs fewer, making it far more tractable.
The gearbox was also replaced with an Xtrac-built six-speed unit, whereas previously they were Prodrive-built. With the specific and unique demands of the Safari rally, longer gearbox ratios were used to boost top speed and suspension dampers with remote reservoirs were used to cope with the punishing terrain and impacts.
Kenneth Eriksson's Impreza in Service Argentina 1996
1997 – Subaru Impreza WRC97
From 1997 there was a new look to the specifications of cars competing in the World Rally Championship. A new breed of cars was created to the new ‘WRC’ specification. Revised regulations permitted major changes, chiefly to the width of the car, suspension geometry, engine internals and to aerodynamics.
The 555 Subaru World Rally Team were the first to test and launch a World Rally Car in the shape of the Impreza WRC97. The engine in the latest variant was placed further back for more central weight distribution, for many rallies the track width was increased to boost stability, although on certain gravel rallies the narrower track actually worked better as it allowed the car to fit into the ruts left by other competitors.
Based heavily on the superseded Group A Impreza, the WRC97 is perhaps the most iconic of all time, setting the visual standard by which other entries were judged. Renowned auto stylist Peter Stevens was brought in to extract the most from the new aerodynamic opportunities.
The car remained the same length but grew 80mm wider and the bodyshell sat 15mm lower in an effort to reduce the centre of gravity. The compression ratio of the boxer flat four engine was increased, and changes to the manifold and radiator lead to the production of the regulation-maximum 300 horsepower at 1000 revs fewer than previously. Torque was also slightly increased.
The brake discs were enlarged to cope with the generally higher speeds, by 6mm in gravel form and 13mm in asphalt trim. Interestingly the rear asphalt brake discs were actually reduced by 45mm, making them the same size as gravel rears, in an effort to shift brake bias.
Performance development work continued on dampers under the freer regulations, and remote reservoirs were commonly used on all rallies to tackle the issue of fluid heat build-up. As other shifted to sequential gearboxes, the Impreza WRC97 returned to Prodrive-built gearboxes and was the only car to use their pioneering H-pattern layout.
In-car with Colin McRae and Nicky Grist, Portugal Rally 1997
1998 – Subaru Impreza WRC98
The Impreza WRC98 was the only car in the WRC to be newly homologated for the 1998 season, and whilst it looked the same, it featured many new developments to further refine the Impreza such as a revised differential layout and further engine tweaks.
One of the more substantial changes was the shift to a fully active differential setup, replacing the mechanical rear differential used in 1997 with an active item. The front, centre and rear differentials were all active in an effort to increase overall traction. This setup was debuted in New Zealand at the end of July. Following this, there were further developments with the differential cockpit controls to allow the driver to take advantage of their greater flexibility.
Suspension work continued and the WRC98 demonstrated revised suspension top mounts and strengthened shock absorber casings. Suspension setups became increasingly more complex during this era with the employment of closed loop active adjustment systems.
Whilst engine power output remained unchanged, the boxer benefited from a new turbocharger, revised crankshaft and other internal components. It was largely the brevity of these changes that warranted a new homologation for Subaru.
There were plans to install a Prodrive-built sequential gearbox for the first time, but these were scrapped in favour of retaining the traditional H-pattern item, albeit a further revised and refined version.
Colin McRae and Nicky Grist in action, Rally GB 1998