On empty race days, create a sprint race and enter it. When it starts, use all your nitro and just keep pressing L near the redline. You will usually win about 95% of the time. On empty race days, host a Class 1 sprint race. Bet all your money on the Dodge Viper, which will usually always win. If there are two Vipers, do not make a bet.
When you have enough money ($10,000 is a decent amount to begin with), host your own event and make it a sprint. Allow only class one cars. This leads to either a corvette or a viper being the competitors. Make sure you always bet on the viper as it is much faster than the corvette. If both drivers have the same car, look for which car has the higher BHP. If they are identical or there is only one car, refrain from betting.