Go into arcade mode and set the race to Speed Racer, while in the gaming lobby you are player one, make five other AI's (player 2, player 3, player 4, player 5, and player 6) Set the AI to Hard by pressing RB and LB, Beat the race five times in a row.
TIP* set all the cars on the track to sport including yours and then have the country set up as follows:
YOU= USA
CPU1=german
CPU2=german
CPU3=german
CPU4=USA
CPU5=german
for some reason you seem to get more boost this way.