The Porsche is a 4.5L motoer and a unique design. The Touareg V8 uses the Audi 4.2L Audi motor. A 450bhp version is available in the RS6... as with any modification it will affect many other sytems governed by the computer.
You can't just turbo a motor or drop in other engines.... better of to just buy a faster car, unless you are willing to make comprimises.
I can't leave anything I drive alone. Our T-Reg is my wife daily driver and she refuses to let me modify it.
I have seriously hot-rodded a 2001 1.8L Audi A4 Turbo Quattro. I sacrificed some drivebility to have performance.
Speed cost money how fast can you afford to go?