Successfully complete the indicated event(s) in the Challenge Series to unlock the corresponding car:

Aston Martin DB9 (Exotic): Defeat Wolf in Boss Battle mode.
Dodge Charger RT Classic (Muscle): Defeat the 21st Muscle Car Gang.
Jaguar XK 2007 (Exotic): Successfully complete all three Turf War races.
Mazda RX7 (Tuner): Defeat Kenji in Boss Battle mode.
Nissan 240SX (Tuner): Successfully complete all three Checkpoint challenges.