Then comes a second version of this V8 455, the SD-455 or "Super Duty" whose performances were similar to those of racing engines. Surprisingly when the glorious era of muscle cars begins to fade. The SD-455 had a reinforced engine block with four bolts with a special camshaft, forged aluminum pistons, forged connecting rods, valves and enlarged enrollment bonus "SD-455" stuck on " shaker ', all for only develop "only" 310 hp officially, which is close to 370 hp in fact according to many experts. Only 252 Trans Am of this type were ordered. The Formula equipped with this engine did not cover the two air intakes but a Trans Am hood because of a desire for approval and only 43 copies were produced.
If the second-generation Firebird was a default until 1974, it was the rear visibility was much reduced compared to that of the first generation cars. The rear side windows have been removed, it was clear that it would interfere with the drivers. Probably pressed by the press and customers embarrassed, General Motors decided to modify the hull of its F-Body. Like the Chevrolet Camaro, they underwent a significant change in aesthetic namely a lateral extension of the rear window. Similarly, the parking lights / turn signals were moved to the outer edges of the grids of the grill leaving the empty slots. The black caps were added to fill those two holes. Thus, it is easy to differentiate the Firebird from 1974 to those of 1975.
Pontiac announced the judgment of this 455 V8, huge disappointment for irreducible heavyweights. The press was of the same opinion and did not appreciate this choice. The four-speed automatic transmission designed for larger engines was also removed, probably because of the bulkiness of the catalyst. Fortunately, Pontiac succumbed to the pressure in the middle of model year and went out in a limited number of Trans Am equipped with the V8 455 Hi-Output below. In fact, it was the same engine of Bonneville break of only 200 hp so nothing very sporting in this engine. To decorate the pathetic side of the thing, the engine was reported by a sticker "455" on the shaker and the dual exhaust system ended with chrome tips doubled. The 455 HO was mated to a manual four-speed. Purely a marketing move, but it sold only in 857.