Defeat the indicated Boss to unlock the corresponding car.

911 Carrera S: MK
Aston Martin Db9: Jenna
Carrera GT and Lamborghini Gallardo: Clutch
Chevy Cobalt SS and Vw Golf GTI: Marcus
Chrysler 300 and Pontiac GTO: Layla 1
Firebird, Toyota MR2 and '67 Mustang: Poorboy
Lotus Elise and Mustang GT: Steve
Mercedes SL65, Corvette and Ford GT: Scotty
Mitsubishi Eclipse: Sly
Nissan 350z: Daemon
Pontiac Solstice: Striker
RX-7, Skyline GTR and WRX STI: Buddy
RX-8, Toyota Supra and Audi TT: Layla 3