Audi S4
Audi's quattro four-wheel-drive system was standard on the C4 S4/S6; a first-generation Torsen-based system which used the "T-1" automatically biasing centre differential (ATB) was used on vehicles equipped with manual transmissions, while a transfer box based system was used on vehicles equipped with an automatic transmission.
Audi 100
Audi released the C4 "(a heavily revised C3)" in late 1990 in Continental Europe and 1991 in other markets, including the right-hand drive British market. The C3-platform Audi V8 continued to be sold as a separate line. The major change for the C4 was the introduction of a 2.8 L, 90-degree, SOHC 12v, V6 engine. It was later joined by a 2.6 L variant, of the same configuration as the 2.8 L unit. They are essentially the same engines offered in the 1992, B4 Audi 80. The option of quattro permanent four-wheel drive was an option across the range, and the Audi 100 quattro was available with a ZF four-speed automatic gearbox.