Some race events are listed as "Boss Race" in the event description. Win that event on the gold difficulty setting to be awarded that Boss' car. When you win a Boss car, it will appear in the Pocket Garage, and you can race it in any game event.

Successfully complete the last race of a set with a gold medal to unlock bonus parts.

In the Nitrous Run Race, if your time is about two to four seconds from expiring, aim the car at the gate and use all the nitrous remaining. Even if the timer runs out, your car will keep going enough without the gas and may pass the gate. If so, the timer will start again and your nitrous tank will be refilled, allowing you to continue with the race.

The following cars are unlocked for purchase in order:

Volkswagen Golf GTI 2.0L: $22,000
Ford Focus ZX3: $18,000
Mazda Miata MX-5: $19,000
Dodge Neon: $17,000
Nissan Sentra SE-R SPEC-V: $21,000
Toyota Celica GT-S: $23,000
Nissan 240SX: $30,000
Mitsubishi Eclipse GSX: $32,000
Mazda RX-7: $34,000
Mazda RX-8: $48,000
Pontiac GTO: $46,000
Subaru WRX STi: $46,000
1969 Dodge Charger: $44,000
Toyota Supra: $52,000
Nissan 350Z: $54,000
Mitsubishi Lancer: $51,000
Ford SVT Mustang Cobra R: $56,000
1967 Ford Mustang: $65,000
Nissan Skyline R34 GTR: $70,000
Chevrolet Corvette Z06: $72,000