(http://media.il.edmunds-media.com/mclaren/mp4-12c/ns/mclaren_mp4-12c_actf34_ns_70111_196.jpg) McLaren's new GT3 racecar — the company's first car built for racing outside of Formula 1 since the McLaren F1 GTR — will appear in revised form this weekend at the Goodwood Festival of Speed.