I would say it does not matter so much what camera body, but more what lens you have. If you plan on photographing drag racing, you'll need a flash or two as the races run into the night.
You'll need a telephoto lens for road racing, because unlike drag racing, there are excellent photo spots right next to the track you often cannot stand in due to saftey.
I would not want to photograph sprint racing, as there are often no particularly good spots to stand outside the pit. In the pit, near the sidewall, your camera is going to get incredibly dirty and may shatter a lens if it's unprotected. You'll need filters you're willing to lose, and spares. You're going to be standing in spots where rocks and other debris fly.