Back in the late 50s and early 60s there were many flat heads used in stock cars that ran on the short dirt tracks in the Delaware, Maryland and Pennsylvania area. They did okay but never lasted more than one or two race weekends, usually blowing out the rings and pistons. The really fast cars ran the big GMC straight six truck engine with a home made intake and 3 carbs similar to what the first Corvettes had, home made headers and a cam that was specially made by Isky. It was around 261 cubic inches and had tons of torque and the racers usually hooked them to a home made sort of crash box with only two gears, one to get started and one for on the track. Here's a couple of pictures from the Little Lincoln Speedway in Lincoln Delaware.
