Game shark codes:

Master code "must be on"
0E3C7DF21853E59E
EE9A6CD2BCBCC5FA
  
CPU cars goes mad!  
DE8BA47EBF899B8B
DE8BA47ABCA99B83  

No tire wear  
DE9DB46EBF899B8B
DE9DB46ABCA99B83
  
Unlimited fuel  
DE9DA34EBF899B8B
DE9DA34ABCA99B83