I haven't ever seen the F.A.S.T. races in person but they're my favorite to watch on video.
First and foremost, the ¼ mile times they run are amazing, in particular being limited to the factory size and style tire they originally had. I have seen a "behind the curtain" video of what one of the TOP "stock appearing" cars, a L88 Corvette, does to those tires to prep for the track. Up front, they are running in the mid to high NINES in the 1320!
They have a machine that does much of the process of shaving the tread down, they melt some off if I remember correctly, and so on. Regardless of prep, the grip is impressive.
2 classes AFAIK in F.A.S.T. Pure stock and the faster class lets them do just about anything to the engine as long as it looks factory.
Hemis, 440 6bbl cars do well, but I believe the L88 'vette has advantages that can't be overcome due to how "hot" they were from the factory.