Slated for an early debut next year at the Detroit Auto Show, the 2011 Audi A8 is one of the most thought-after luxury sedans. Caught testing on the Nurburgring circuit, rumors have it that the upcoming model comes with new engines. Apparently there’s the new 6.5L V12 which replaces the 6.1L variant for a monsterish output of over 500 horsies, or the supercharged V8 capable of churning 400 hp. Mileage is also on the priority list for Audi which means the new A8 lineage will also include a 2.0L diesel option mated with twin turbos that sport some 200hp. For those who can afford it, sales will begin late 2010. [via Autoblog]