There were in excess of 200 racers at the track in a variety of classes, 125 2-strokes to liter bikes. The most popular seemed to be Suzuki SV650s. After watching a couple of races and chatting with others spectators, we figured out that the two fastest guys were really in a class of their own. The brand of bike is a minor part of the equation, we heard the "fast guy" mention while being interviewed that he'd been racing at Oak Hill for 17 years.
You can get a sense of the track by going to YouTube.com and searching "oak hill".