Looks like a CR500 motor, pretty sweet looking though I'm not an aluminum frame fan (too much feed-back off-road). I can see why he'd used a 500 2str in a newer chassis for a rythm/whoop race. Our '04 KX250/500SF conversion is to this day, the best bike I've ever ridden in the whoops. There is no wrong gear, it just goes straight and stays on-top with next to no effort.