Audi S6
Audi made a high-performance, 4.2-litre V8 engine (parts code prefix: 077, identification code: AEC) with a Bosch KE-Motronic ECU available as an option in the original European S4s, and made the decision to continue to do so with the S6, making a version of the 4.2 available as an optional upgrade over the 2.2-litre inline five-cylinder turbo. Unlike the five-cylinder turbocharged version, the V8-powered S6 was supplied with a four-speed automatic transmission as standard, but kept the quattro four wheel drive. A six-speed manual gearbox was also available as an option.
Audi RS 4
The B7 RS4 was planned to replace the C5 RS6 in the SCCA Speed World Challenge, but after Champion Racing had prepared the car, it was decided not to compete in the series, due to rule changes imposed by the Sports Car Club of America (SCCA) on Audi concerning 4WD systems, wheels size, and engine power output. Rather than scrapping the fully built Speed World Challenge RS4, Champion and Audi used the car as a part of the American Le Mans Series Vitesse Program, which highlights the technology link between race cars and conventional series production road cars.