Custom Corvette Mode
To get custom corvette mode, you have to win all the races in C3 career mode.
Circuit Endurance Mode
Win all the C4 career mode races to unlock this race mode.
Hot Lap Challenge Mode
Win all the C2 career mode races to unlock this race mode.
Route 66 Checkpoint Mode
Win all C5 career mode races to unlock this race mode.
Unlock Everything
Go to options and go to "change name" and put "xopensez".