Here are the Basic Rules
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. That's valued at, as assessed by the general market, not what you paid for it.
Personal safety gear includes a Snell SA helmet and SFI-FIA certified driver's gear.
Strip out all the interior and take out all the glass, except the windshield. Install the roll cage, seat and harness. Add some numbers and you have just created a $500 race car. Okay, so there's more to it than that, but not much. Read the rules to fill-in the blanks.
You can upgrade the brakes a little but don't even think of adding any trick racing suspension crap. Tires are up to you... as long as they're DOT legal and rated for treadwear according to the rules.
ChumpCar has various race formats, but they're all endurance racing... ranging from 7 hours to 36 hours. You'll need a minimum of 3 drivers for most events - 4 for the longer 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... 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 you'll never win. If that doesn't bother you, you're our kind of Chump!