For the second year of the second generation Firebird little was changed. The fenders of Firebird, Esprit, and Formula models acquired a louvered air extractor. Oddly in 1972 the fenders returned to the look of 1970 making the 1971 model the most unique of the first design second gen. GM edict also required all cars to run on unleaded gas this year forcing cylinder compression to drop. Because of the horsepower drop that went with the drop in compression GM waived its edict restricting the largest engines from being placed in mid size cars. The Trans Am now came standard with a 455 cubic inch engine in HO guide, the biggest ever put in a Firebird from the factory.The 455 was optional in the Formula which now diversified into Formula 350, Formula 400, and Formula 455 models from the previous Formula 400 marque.