On completing the one player championship with first place in the drivers championship and first place in the constructors, you will unlock the following.

Unlockable	How to unlock
1960's Bullet Car Type	First in Drivers Champ and Constructors.
1976 Tyrrell 6 Wheeler Car Type	First in Drivers Champ and Constructors.
S Level Driver Type	First in Drivers Champ and Constructors.
Unlock Secret Fictional Track	First in Drivers Champ and Constructors.
Unlock Secret Fictional Track - Oval	First in Drivers Champ and Constructors.