>how hard can it be to produce more engines??

Let me break this down for you ONE LAST TIME. Whatever production line
adjustements where neccesary for production of the W12 had already been made,
when Audi introduced the engine in 2001. They weren't interested in re-tooling
a mere 2 years later simply so a different engine could be used. The facilities
that handle production of the Lambirghini engine are small, and incapable of
producing enough units per year for both the A8 *and* the Murcielago. DON'T YOU
GET IT?

>why not just turbo charge the
>W-8 and get similar horse power to a V-12.

Audi found out over many years that larger displacement motors are often more
impressive to buyers than smaller, turbocharged mills which appeal mainly to
tuner and enthusiast crowds. This is one of many reasons they choose a version
of the 4.2 litre V8 for the S4 and not a bi-turbo version of the 3.0 litre.