How close will you be standing to the track?
If you want static shots, camera in shutter priority (Tv mode) and aim for 1/600th or higher. Keep an eye on what is going on with the aperture and if needs be crank up the ISO. If you are getting the exposure right you can happily get away with ISO800 if you need to (though if its that dark you might struggle with colours/contrast etc).
If you are panning, you will need to judge an appropriate shutter speed really, depending on a few things. Panning is a technique that needs practice, dont expect to have a kigh keepers ratio straight away. Start reasonably slow (1/250th) and get slower until you are getting it right. Use the LCD preview to check on things regularly. If you are going to be close to the track, the 70-200mm might not be the best choice of lens. I have been stood trackside at somewhere like Mallory Park and I was panning away with the 50mm - anything else would have been too long.
Hope this helps!