Audi Ur-S4 / Ur-S6
The Ur-S4 was produced from 1991 to 1994, while the Ur-S6 was produced from 1995 to 1997. They both featured a 2.2 litre, 5-cylinder engine with turbocharging and an intercooler, with of torque. In Europe, V8-powered versions of both S4 and S6 were available. The S4 version sported a engine (the same "ABH" engine as in Audi V8), the S6 had an upgraded engine "AEC" with . American versions featured a 5-speed manual transmission and in Europe a 6-speed, as well as a 4-speed automatic transmission could be substituted.
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.