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 S4
Don Istook, with Istook's Motorsports, built and campaigned several B5 S4's in first the Motorola Cup, and then the Grand Am Cup. The S4's were even raced by Istook's Motorsports in the Rolex GT category for several races to help fill the field. Of note, one of the S4's, racing against true GT cars, even ran as high as second place (in the rain) at Barber Motorsports Park. These S4's were built using existing S4, not RS4 engines, but used the B5 Audi RS4 K04 turbochargers.