Bass Pro Series. I've never done it but from what I hear its a great racing scene. I am just now getting into RC with my 5 year old son, and getting ready to build a dirt track in my back yard. These guys can help you:
http://www.nitrotoysandhobbies.com
Here is the link to the Bass Pro Series:
http://www.rcracingxtreme.com/
I just wish we still had a public access track. I heard the guy lost the lease on the land. Maybe one day it will come back.