Expected to debut at the Detroit Auto Show this January, the Audi A8 has been caught testing at the Nurburgring racing track and word is, Audi’s flagship model will have a new set of powerplants.

The powerful W12 engine will continue to top the A8 range, but power is expected to grow from 6.1 to 6.5-liters and exceed 500 horsepower. Below the W12 will be a supercharged V8 with more than 400 horsepower and a cylinder management system that could shut down up to four cylinders.

Audi also seems to be working on a less powerful but more efficient 2 litre diesel bi-turbo engine with just over 200hp to also power the next of Audi A8s.

We can’t give you the prices yet on the new Audi A8, but sales are likely to begin in late 2010.