Not including the required safety equipment that you'll need - roll-cage, racing seat, racing harness -- your car must be valued at less than 500 points. What does that even mean?
ChumpCar uses a points-based system to value the cars. Each make/model is assigned a specific base point value. Performance items- shocks, springs, engine modifications, etc. are assigned additional points. Your car’s total point value cannot exceed 500 points (see the rules for how to do this). ChumpCar uses this point-based system to control the cost required for a team to go racing.
Strip out the interior and take out all the glass, except the windshield. Install the roll cage, seat, fire-suppression system and harness. Add some numbers and you have just created a race car. Okay, so there's more to it than that, but not much. Read the rules to fill-in the blanks.
ChumpCar has various race formats, but they're generally range from 7 hours to 24 hours. You'll need a minimum of 3 drivers for most events, and it's wise to have a couple of crew guys as part of the team. Get people on your team that know what end of a screwdriver to use and can think clearly at 3:19am when a wheel bearing starts to disintegrate.
If you cheat or screw-up or both... you'll be docked laps. If you come to Tech Inspection with a car that's worth 1,500 points... plan on starting the race about 100 laps down from everyone else. You can still run in the race and you'll have a great time... but at that point, you'll only have photos to show for it.