Yeah I know I'll have enough reach for sure. I'll be at Irwindale Speedway most of the time and its only 1/2 mile around. The test run will be at the end of this month and I'll be sure to let anyone interested know how it went.
Night time action shooting can be a nightmare with slow glass. I imagine racing you need really fast shutter speeds close to 1/800 or 1/1000. I shoot basketball and football and can't go under 1/500 or 1/640 without motion blur.
Is that a big track with pro racing going on or is it small where anyone can pay a little money to run their car? If its a professional race you might be out of luck even getting an SLR in... and certainly not any larger glass that would be fast enough to shoot, stopping the action.
The lens you have should be great for most applications, just not nighttime when you need high shutter speeds.