Pretty much everyone has been posting this but this is the full version.
First go to a free day, one that doesn't have blue. Then press x and you will get into the create a race section.
Make the race type a sprint. It will start out as a point to point. Then make it a class 1 race.
Push right twice to get the race mode into sprint.
Then push x for everything else. To make the race you must have 1,000 dollars.
After that press watch sprint.
If the two cars are the same don't bet. If it is Viper vs Corvette then bet all the possible money on the Viper