Audi A6
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
Replacing the 2.7-litre 'biturbo' V6 engine of the previous generation B5 S4, the new B6 S4 powertrain gained an all-aluminium alloy 4.2-litre, 40 valve (five valves per cylinder) V8 engine (parts code prefix: 079.C, identification code: BBK), with chain-driven double overhead camshafts, roller-finger rocker arm cam followers, and included variable inlet camshaft timing. It also used a strengthened alloy crankshaft bedplate for the five main bearings, and a two-part baffled oil sump, and a light-alloy variable intake manifold (VIM), containing the fractionally sequentially actuated fuel injectors. This petrol engine, based on the unit from the Audi A8, displaces , and it produces a motive power output of at 7,000 rpm, and generates torque of at 3,500 rpm, making it more potent than the RS2 Avant, and nearly as powerful as the B5 RS4. Engine management was by way of a Bosch Motronic ME 7.1.1 electronic engine control unit (ECU), using a Bosch 'E-Gas' drive by wire electronic throttle, and powering eight individual spark coils with longlife quad-electrode Bosch spark plugs. Ignition timing is a mapped direct ignition, with cylinder-selective knock control with the aid of four knock sensors. The exhaust system includes vacuum-operated valves in the twin rear silencers (mufflers), finished with chrome plated tail-pipes.