Audi’s top-trim cars, the next S5 will have a V6 instead of a V8 engine when it comes out in 2009. The S5 will get the new 329-horsepower supercharged V6 engine that is on call to replace the age-old 4.2-liter V8. The V8 was used in the previous S4 as well other high-line Audi models.
Weight has been an issue for the current S5, affecting the power and torque - the much lighter V6T engine can be expected to be a big improvement in those areas.

In addition, the next Audi S6 will swap its V10 for an updated twin-turbocharged version of the 4.2-liter V8. Audi will likely make the same move for the S8, leaving the V10 biturbo version to the higher-performance R8 coming next year.

[Source: insideline]