Thanks everyone, it was a nice opportunity to practice as I did not have to elbow my way to a spot with a clear view.
Dal, you are pretty close, out of 290 about 60 actually were decent enough to play with. I picked these ones based on being either the sharpest or the car having a fancier paint job.
Scott, I wish I hadpicked up on the SR settingas quickly as you did. It was not until I was done shooting that I noticed it was still set to 100mm. I don't know that it made much difference.
I think panning with a manual focus may be easier than auto (never tried it though). I just prefocus on the section of track where I want to make the shot, pick up the car approaching me in the viewfinder, and follow it through shooting a three shot burst. If there is any secret it is keeping your upper body and arms rigid and pivoting only at the waist.
Thanks again for the kind words, I am looking forward to trying it with some different lens combinations.