S6 uses a version of the 4.2-litre 40-valve (that's not a typo) V8 engine that powers the S8 and A6 4.2 quattro. This little number produces 250kW at 7000rpm (creating a power to weight ratio of 6.9kg per kiloWatt) and 420Nm at 3400rpm, with close to 300Nm available from just above idle speed. The burst from standstill to 100km/h is a claimed 6.7 seconds. Fuel consumption is not a strongpoint, European figures pointing to 21.8 L/100km on the city cycle and 10.1L/100km on the highway. Though based on the 220kW/400Nm A6 4.2, the uprated performance of the S6 was achieved though a range of measures, including a retuned magnesium variable intake manifold with two-stage length adjustment (the longer air intake path enables high torque at low speeds, the shorter one full power at high speeds). Higher-lift and retimed camshafts aim to ensure optimum cylinder filling, with the inlet valve timing matched to the engine's relevant operating point by a hydraulic camshaft actuator. At higher engine speeds an additional vacuum-controlled flap opens in the air cleaner housing and enables the engine to breathe more freely. The revised exhaust system with reduced back pressure has a high gas flow rate and creates a rorty note.