Here is a sound track of a Turbo revving.
Got this off the 6speed site. In a word, the sound is pathetic. Very sad.
http://www.youtube.com/watch?v=C6xDPtGWME4&search=porsche%20997
http://www.youtube.com/watch?v=C6xDPtGWME4&search=porsche%20997