Instructions
Purchase the Chevrolet Corvette ZR1 '09. This car cost 184,800 credits to purchase. This is a powerful car from an American manufacturer. This is a relatively inexpensive car, but can easily win the American Championship without much skill. It is also one of the few cars capable of getting the Race Mod upgrade.
Purchase the Race Mod upgrade. This upgrade costs 345,000 credits on the Corvette ZR1 '09. The Race Mod is a large-scale upgrade of almost the entire car. This causes an increase in the speed and handling of the car, making it perform much more effectively.
Purchase any additional upgrades you want to add. This step is optional.
Compete in the American Championship using the Chevrolet Corvette ZR1 '09. You should have little difficulty winning the race, even with mediocre driving skills due to your car performance advantage. You win 97,600 credits for winning this race, which only lasts about four to five minutes.
Replay the American Championship until you reach the desired amount of credits.