The guys who brought you a VW Jetta powered by a VR6 and turbo W8 are now swapping a 6.0 L W12 engine into a second generation Audi A6. The biggest engine the A6 came with was a turbocharged 4.2 L V8 and you can see how much space the W12 takes up. The W12 produces around 444 horsepower and 430 lb-ft of torque. The project still needs some work such as custom motor mounts and wiring but when complete will be one really unique Audi sedan.
Source: Punchbuggies Racing