The Group A rally car begins with a bare Subaru Impreza WRX RA shell straight from the Subaru Factory production line which is then prepared by Prodrive.
All the unnecessary brackets and unwanted parts are removed. A complex yet substantial multipoint roll cage is specially designed by Prodrive, fabricated using 38mm steel tubing and TIG welded into the shell.
The roll cage braces all the suspension points and vastly increases the torsional rigidity of the shell. The shell is seam welded and the rear of the cabin bulkhead is sealed with an aluminium honeycomb reinforcing panel.
The gearbox tunnel is modified to accept the Prodrive 6 speed gearbox and running gear along with the front suspension turrets (which are heavily reinforced) as the Group a engine and suspension sits approximately 20mm further back in the chassis. To further accommodate this the front and rear wings and wheel arches are cut back and flared slightly to prevent the 18” wheels rubbing and provide better clearance.
Further suspension bobbins and mounting points are added to the shell to accept the tubular rear subframe. Mounts were also added for the 75 litre fuel tank in the boot and also the water injection pump behind the drivers seat, some but not all shells were fitted with a spare turbo bracket. Additional dust seals were added along with extra brackets for the special lightweight wiring harnesses.
The front chassis rails were double skinned at the front bumper mount and bracket mounts added for the sump guard. A known weak point was the Impreza sills so they were also double skinned along with fitting of sill jacking points.
Finally seat rails were welded in as the drivers and navigators seats are bolted to floor for safety. With all these modifications and safety additions the shell still only weighs 230kg but all this preparation work takes upwards of a 1000 man hours.