It used to be .15 size 100 laps on pavement.  I think there was an A class with BB motors and shutoffs, and a plain bearing class.  That was a while ago, 1970's.  Then the was the Fox .35 class that was run on grass with a builtup wing usually, Then they changed the motor to a .25 LA. 10% nitro.  They are a little faster, maybe they don't start as good after a hot run, they definately don't shake as much. They are running July 6 or 7 in Dresden Ont. Canada. 70 laps, 140 lap final.....