Audi Sport UK Press Release from 28/10/1981 with technical specifications of the Audi Quattro in Group 4 specification.
All rights to the content belong to Audi, I am merely posting the information for historical purposes – Double G.
Modifications to the Audi Quattro for rallying
Floor reinforcements and aluminium roll cage extending from the front bumper through the whole vehicle.
Aluminimum dashboard with special instrumentation and quick-release catches. Racing seats and extinguisher system. Aluminium front bumpers, bonnet and doors; plastic boot lid.
Four ventilated discs with bolt-on aluminium hubs, light alloy calipers and adjustable brake pressure regulator (no hydraulic servo), hand brake acting hydraulically on rear wheels.
Power assisted, driven off the camshaft.
5-speed gearbox with special ratios for rallying
1 – 3.00
2 – 2.00
3 – 1.50
4 – 1.217
5 – 1.040
Differentials: 4.11, 4.55 or 4.87
Wishbones, steering knuckles, tie rods, springs, shock absorbers and stabilisers strengthened and , where permissible, adapted to suit the difficult service and repair conditions in a rally. Similar measures adopted fore the mountings for engine, gearbox, rear differential and front and rear subframes. Aluminium underbody guards front and rear.