Get a long (mine is 12ft ) 3.5-inch audio cable and a small lapel mic to put near the exhaust or in the engine bay. Otherwise you’ll just get wind noise at speed. If you have the new HDHero 3, you’ll also need an adapter cable from GoPro.
No Mic: [video]http://www.youtube.com/watch?v=Hm160DcBhYM[/video]
Mic taped near the exhaust: [video]http://www.youtube.com/watch?v=iN6qFoEbfHc[/video]