From Templins interview:
Car & Driver: Why don’t you use turbochargers on the F cars?
Mark Templin: [F program chief engineer Yukihiko] Yaguchi is a big fan of naturally aspirated engines because of the visceral effect that you get, the sound of it, and the way that it feels. That being said, it doesn’t mean we’ll never have a turbocharged F product, but if we do, it will probably be a big engine that still gives you all of those attributes that he wants. He really feels that it’s important to have the sound quality that you get out of those big engines.