 Federal emissions laws eventually brought the horsepower era to a close and resulted in a steady decline for Pontiac's engines.One holdout to this industry-wide slide was the Super Duty 455 engine of 1973–1974.Available only in the Firebird Formula and Trans Am models, this was rated at net initially but after having issues passing EPA emissions tests, the camshaft was changed to the old RA III cam and with the change, came a net rating.