The Audi S6 4.0 TFSI quattro and its mechanical twin S7 were launched as a 2013 models, a year after the C7 Audi A6 and Audi A7 were released. The Audi S6 and S7 are powered by a 4.0L DOHC twin-turbo V8 engine mated to a 7-speed S-tronic Double Clutch Gearbox. This engine makes 420 hp and 405 lb-ft of torque, plus there is a cylinder-deactivation system and a stop-start system for improved fuel economy. The 2013 Audi A8 shares the same engine, while the 2012 Audi S8 has a variant of the powerplant in a higher state of tune making 520 hp and 479 lb-ft of torque, both mated to an 8-speed automatic transmission.