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 S4
The powertrain details of the B5 S4 feature a 2.7-litre twin-turbo ('biturbo') 90° third-generation V6 engine (parts code prefix: 078, identification codes: AGB, AZB, APB). Details of the powerplant include a cast iron cylinder block with two lightweight aluminium alloy cylinder heads. The valvetrain includes 30 valves (five valves per cylinder), twin hybrid-driven (timing belt and roller chain) double overhead camshafts and variable valve timing for the inlet valves. The intake air is pressurized by two parallel water-cooled BorgWarner K03-series turbochargers; the charged air is cooled by two side-mounted air-to-air intercoolers (SMICs). It displaces , and is rated to produce a motive power output of at 5,800 rpm, and generates of torque at 1,850 rpm. Engine management was by way of a Bosch Motronic ME 7.1 (7.0 in North America) electronic engine control unit (ECU), and helped it meet the European EU-3D emissions standard. In all US-market cars, the engine was detuned to meet US emissions regulations; output was reduced to and (identification code: APB).