[Jim B]

The biggest single reason for the sudden low horsepower ratings in the early 70's was that was when the auto insurance industry began factoring horsepower ratings into the insurance premium risk calculations. Some of the lower hp ratings were due to the horsepower/torque numbers being obtained at a lower rpm than early ratings as well as the "was gross now it's net" smokescreen to avoid lost showroom sales due to the "higher horsepower = higher insurance premium" factor. Add to that was Washington frowning on high horsepower offerings from the manufacturers. There was even early discussions in Washington on a potential "horsepower" tax on the car manufacturers. (similar to the "gas guzzler" tax imposed on auto makers for a high CAFE (Corporate Average Fuel Economy) rating that did become a reality. The auto companies were just proactively dodging a bullet.