Raymond,
I was in a real good location, no fences to shoot through and able to pan on cars for maybe 1/4 mile before they got to me. I was using a 70-300mm lens. The first pic posted was at 160mm, 1/180 shutter speed, f11, iso 200. I have tried a lot of different shutter speed and this is the slowest I have shot for racing and got these results. (When I first started I shot a lot faster.) The lighting was mixed but look at the shadows directly under the cars and you can see where the sun was.
Good luck, look forward to seeing your photos.
Bill