2009 Audi RS6 - Click above for high-res gallery
The next generation Audi A6 is expected to debut early in 2010 and that means a new performance S6 and super-performance RS6 will likely follow a couple of years later. As improved efficiency and reduced CO2 emissions take hold in the early years of the next decade, that almost certainly means the S6/RS6 will follow the trend of this year's new S4 and down-size its powerplant.
The larger RS6 is currently propelled by a twin turbocharged 5.2-liter V10. The V10 which is shared with the Lamborghini Gallardo (in normally aspirated form) will likely give way to a smaller, boosted V8 that should be lighter and more compact. In all likelihood, the smaller engine won't result in a reduction in performance and will probably be in the 4.0-4.5-liter range with either supercharger, turbos or perhaps both. Recent rumors have indicated that the next M5 will follow the same path taking on the 4.4-liter twin-turbo V8 from the X6 M.