Hmm, its not allowed in the regulations for the GTR. They could have done it for the normal McLaren F1, but Gordon Murray wanted a car which gave an instant response. Naturally aspirated is the way to go for that. Also, the car was designed around 1992. For its time, 630 bhp was UNTHINKABLE. It wasn't beaten until recently i.e. when the Bugatti came along.
sweet!, well they must of heard me lol, because they've done it now! with the mp4-12c cool :-)
Naturally aspirated engines sound better and give instant response. In an engine bay that can fit a 6L V12, you would have to reduce the size and number of cylinders if you wanted turbos