More horsepower! Is what wanted PONTIAC, 1973 year saw the birth of a new engine, the SD-455. SD for Super Duty , this engine did not have much in common with the base 455 and was hand assembled. Block reinforced, specific rods, four bolts per bearing, special pistons, high pressure lubrication system, camshaft and all hi-perf distribution, round, exhaust ports, big valves, polished combustion chambers, special intake and dual exhaust. All this equipment produces 310hp and T/A ran the quarter mile in 13.54sec at 104.29mph. Only a few 310hp engines saw the light because they did not meet emissions standards and a new SD-455 of 290hp (only) replaced it from March 15, 1973.
Esthetically speaking, no major change except (again) the front grill square-shaped, but larger (the size of an egg) than the 70-71 versions. The front bumper is modified to meet the new standards collision. terms. Most outstanding is the abandonment of the longitudinal band of Trans Am decoration to the benefit of a large"Screaming chicken" sticker "on the hood. This bird on fire (fire-bird) is simply a legendary Indian symbol back into fashion days. It was optional and available in 3 colors: Black / Yellow / Orange paint Buccaneer Red, Green / Light Green / Black hinge on Brewster Green, had to Blue / Light Blue / Black on White Cameo paint. Note that the T / A SD-455 did not have this decal. Those who did not choose this option, still had a small eagle on the front bumper.
Only 252 trans am and 43 formula (that unusually were shaker equiped) had to receiving the 455 SD . The HO 455 "round port" of 72 will be more than a 455 standard "D port" for 1973. Formula Hood vents T/A have been sealed, noise standard requires.
The new front bumper capable of absorbing shocks up to 5mph has advanced the grilles to allow 4" room of urethane foam located in the central part. Added to this, the metal reinforcements from top to bottom.
The Trans Am ordered with automatic transmission but without D55 option (center console), had the shifter mounted on the steering column. Same for T/A 455 .