1973 Pontiac Firebird Trans Am: The Super Duty That Arrived After the Party

Pontiac announced the Super Duty 455 at a press preview in June 1972 with a number that looked like it belonged to another decade. Rocky Rotella, the Firebird historian, records the initial rating as 310 net horsepower at 4,000 rpm and 390 lb-ft at 3,600 rpm, with a 308/320-degree camshaft stamped K. On November 3, 1972, Pontiac published a revised figure: 290 horsepower at 4,000 rpm and 395 lb-ft at 3,200 rpm. The 20 horsepower that disappeared between a summer preview and an autumn correction are the story of the 1973 Trans Am in one line. Pontiac had built a real performance engine, and then had to fit it through the rules of 1973.¹

Why the cam changed depends on whom you read. Rotella writes that the K-cam engine was compliant with the EPA's 1973 federal standard but could not meet General Motors' own internal standard, so Pontiac released a milder 301/313-degree camshaft, part 493323, for production in late October 1972. American Collectors Insurance quotes engineer Skip McCully's view that emissions regulations kept the engine from ever reaching production in the form its builders wanted. The compiled tables disagree in the same way: Tran-Zam lists the SD-455 at 310 horsepower and 390 lb-ft, the preview rating, while MuscleCarClub gives 290 and 390. Both ratings are net figures, and both belong in the record with their dates.^1,2,3,4

The engine came out of racing. The Pontiac Preservation Association's biography of Herb Adams says Pontiac's Special Projects group developed the SD-455 from engines built for SCCA Trans Am and NASCAR competition; Adams credits teammates Jeff Young and Tom Nell, and Rotella names the three of them among the development team. The biography adds a remarkable coda. Adams proposed to general manager Martin Caserio that Pontiac build and sell the roughly 600 sets of Super Duty parts it had stockpiled, and that proposal, it says, was his last day at Pontiac: his racing work had become “all too obvious to General Motors.” The account is retrospective and comes from Adams's side, and it is told as his.^5,1

Caserio also decided where it could go. Rotella writes that the Super Duty had been planned for Pontiac's A-cars, the LeMans, GTO and Grand Am, for the Grand Prix, and for the Firebird, and that Caserio's stipulation was that it be offered in the Firebird only. That left the Formula and the Trans Am as the only Pontiacs that could have it, in a year when, as American Collectors Insurance puts it, muscle-car production had largely stopped under insurance costs and fuel worries. Pontiac's rivals were not answering the Super Duty so much as leaving the field. The Trans Am, sold as a road-racing replica, became the place Pontiac kept its biggest engine alive.^1,2

It was not a dressed-up standard 455. American Collectors Insurance describes a strengthened block with four-bolt main bearings, a nodular iron crankshaft, and the production 493323 camshaft with 1.5:1 rockers. It also reports that the pre-production test cars ran the earlier 480737 cam and functional hood scoops that customer cars did not get, which is why period impressions and showroom reality should not be merged. The same feature makes a pointed certification claim: that the Super Duty needed only a 4,000-mile break-in emissions test instead of the 50,000-mile protocol, because EPA data already existed for the ordinary 455. That explanation is attributed to the article and awaits a Pontiac certification document.²

Then came the wait. Rotella dates the SD-455's release for production to May 1973 and its arrival on the Firebird assembly line to early June, almost a year after the preview and at the very end of the model year. A buyer who ordered one paid $521 for the option on a Trans Am and $675 on a Formula, according to Tran-Zam's option list. The ordinary Trans Am already came with the L75 455 four-barrel, rated at 250 net horsepower and 370 lb-ft; the Formula could take that engine for $154. Tran-Zam also records that 1973 was the year the large Trans Am hood decal joined the option list, at $55.^1,3

The production figures show how short that window was. Tran-Zam and MuscleCarClub count 46,313 Firebirds for 1973, 4,802 of them Trans Ams, about 10 percent of the line. Of those Trans Ams, 4,550 had the L75 455, 1,420 with manual transmissions and 3,130 automatics, and 252 had the Super Duty, 72 manual and 180 automatic. That is about one Trans Am in 19. The Formula count is smaller still: 43 SD-455 Formulas out of 10,166, 33 manual and 10 automatic, a split Tran-Zam attributes to High Performance Pontiac's August 2002 issue. Rotella's total of 295 Super Duty Formulas and Trans Ams for 1973 matches the two rows added together.^3,4,1

Most 1973 Firebird buyers were shopping for something else. Of Tran-Zam's 46,313 cars, 39,931 had automatic transmissions, about 86 percent; 30,597 had air conditioning, about 66 percent; 46,111 had power steering, nearly all of them; and every car on the list had front disc brakes. Only 4,237 four-speeds were installed across the entire line. The Esprit, with 17,249 cars, was the best seller, and even Tran-Zam's own Esprit engine rows over-run that total by 50. Two pages of the same site put vinyl-roof installations at 12,443 and 12,943. Those are small disputes, kept visible, inside a clear picture: the Firebird had become a comfortable personal car with a very fast top model.³

The rating dispute is also a lesson in how the car should be judged. A 290-horsepower net rating from November 1972 and a 310-horsepower preview figure describe two different camshafts, not one engine rated carelessly, and the customer cars built from June 1973 carried the milder 493323 cam. Period magazine impressions were formed with pre-production cars that American Collectors Insurance says ran the K cam, so their numbers belong to those cars. The honest comparison is between what Pontiac previewed, what it certified, and what it sold, and in 1973 all three were different things. That difference does not diminish the Super Duty. It shows what it took to sell one at all.^1,2

The Super Duty had one more season in it. Rotella counts about 1,000 more SD-455s built for 1974, then the engine was gone, and with it Pontiac's link between the Trans Am and the race engines it had come from. That makes 1973 the first of the two Super Duty years: 252 Trans Ams, built in a few weeks at the end of a model year, with an engine that Herb Adams's colleagues had developed from racing parts and that General Motors had allowed to exist only in a Firebird.^1,5,3