How to unlock upgrades:
Drivetrain bonus upgrade: get over 50 points in the Dyno Run1 mini-game
Engine bonus upgrade: get over 100 points in the Nitrous Tuning 1 mini-game
Suspension bonus upgrade: get over 100 points in the Dyno Run2 mini-game
Turbo bonus upgrade: get over 150 points in the Nitrous Tuning 2 mini-game
Nitrous bonus upgrade: get over 175 points in the Nitrous Tuning 3 mini-game
Exhaust bonus upgrade: get over 2,000 points in the Engine Tuning 1 mini-game
Wheels bonus upgrade: get over 4,000 points in the Engine Tuning 2 mini-game
Chassis bonus upgrade: get over 5,000 points in the Pressure Tuning 1 mini-game
Controls bonus upgrade: get over 5,000 points in the Engine Tuning 3 mini-game
Brakes bonus upgrade: get over 7,500 points in the Pressure Tuning 2 mini-game