1972 marked the change from Gross HP to Net HP ratings. Before the change, they would test the engines with no accessory drive, not even a water pump, use head

1972 marked the change from Gross HP to Net HP ratings. Before the change, they would test the engines with no accessory drive, not even a water pump, use headers instead of a full exhaust, and adjust the carburetor/ignition to provide the best numbers per RPM on the dyno instead of reflecting what the engine actually did in the car.