Sometimes the factory purposely underestimated the horsepower ratings of its cars to receive favorable drag racing brackets. They couldn't lie, so they gave horsepower readings before the engines reached their peak rpm.

A good example was my 1971 340 'Cuda. It was rated by the factory at 275 hp at 5,000 rpm. However, the engine would rev to over 6,000 rpm. At the higher rpm, it produced 325 hp.- a 50 hp difference!