When you complete the game with ALL 51 Gold trophies ALL the cheats and special cars will become unlocked. The final Head to Head with Ravenwest will also become unlocked and consists of three laps around Circuit de la Sarthe that must be done under the Extreme difficulty setting. This race is worth $20 million and also awards you bonus cars which will give you a total of 47 cars in your garage.
When you complete ALL the global events coming in 1st place the final Head 2 Head race with Ravenwest will become unlocked. If you win this race you'll unlock ALL the cheats in the game which are enabled by going to the 'Main Menu' and then 'Options' and selecting 'Bonus Codes'. On this screen you will be able to choose which cheats you want to activate.