The SD-455 Pontiac Trans Am
Today we are gonna look back in time to the great years of 1973-1974 when Pontiac introduced us to the Firebird and Trans Am Super Duty. In a last ditch of tossing power and performance to the public, Pontiac gave the world the SD-455 during a time when horsepower was being tuned down and insurance rates were regulating the norm. I love this engine. Probably the reason I yanked the 400 out of my 1976 Trans Am when I was 16 and dropped in the SD 455 was for it’s sure size, power and big block appeal.
The Super Duty was launched at the beginning of what was to become known as the Malaise Era. A time when oil embargoes, the Clean Air Act, and cheap economy sent muscle cars to the brink of extinction. An era when the GTO, Mustang, and Charger were now shadows of their former selves. Before 1973, horsepower dominated and it seemed the Big Three couldn’t make enough muscle cars to satisfy the buying public. Sadly, they came to be dinosaurs as everything got smaller and more efficient to compete during this time period.
When ya look back at it, just the fact that the SD-455 was produced at all was a miracle, given how quickly high-performance became politically incorrect by the early 1970s. Installing it in the Firebird was another challenge because the F-Body line was very nearly canceled after 1972. Sales for ponycars dropped precipitously as younger buyers sought more fuel-efficient cars. Consequently, Firebird sales plunged more than 56 percent between 1971 and 1972, to less than 30,000. Only 1,286 of them were Trans Ams.
Fortunately Pontiac was filled with passionate people, and they pushed the Super Duty 455 project along. It helped that the engineers were deep into the project when the market turned against high-performance cars, so it seemingly wouldn’t take much to push the SD-455 over the line.
Almost every element of the engine was unique, from the block and heads to the rotating assembly, intake manifold, carb, and more. It was announced at the introduction with a 310hp rating, along with plans to make it available at the start of the 1973 model year. That didn’t happen. Creative interpretation on Pontiac’s part of EPA’s emissions test for certification didn’t go as planned, which pushed back production.
However, it seems the folks over at Pontiac didn’t get the memo. For 1973, Pontiac introduced a version of the 455 cubic-inch V8 called the Super Duty or SD-455. This engine was hand-built with a heavy duty block, forged aluminum flat top pistons, and Rochester 800 cfm four-barrel carburetor. The engine was rated at 290 horsepower at 4,000 rpm and 390 pound feet of torque at 3,600 rpm. Today, these numbers may sound miniscule but in 1973, this was top shelf muscle.
By the time Pontiac recertified the engine, with a revised camshaft and commensurate carburetor adjustments, the horsepower rating was revised down to 290. It was the spring of 1973, but the cars didn’t roll off the line in meaningful numbers, creating a significant customer relations problem. The company had stacks of preorders for cars it couldn’t deliver. By the end of 1973 only 295 Super Duty-powered Firebird models had been built: 252 Trans Ams and 43 Formulas.
The automotive press raved about the Super Duty. Car and Driver tested a 1973 Super Duty Trans Am for their May 1973 issue. With a 3-speed automatic, they were able to run from 0 to 60 in 5.4 seconds and dash the quarter mile in 13.8 seconds at 103.6 mph. You have to admit, those numbers are pretty impressive, even by today’s standards. Compared to the 1973 Chevrolet Corvette LS4 454 with the Turbo Hydra-matic, the Super Duty was one second faster from 0 to 60 and 0.9 seconds faster in the quarter mile.
One thing that robbed the Super Duty of horsepower was the new exhaust gas re-circulation (EGR) valve guidelines mandated by the government. Pontiac attempted to circumvent the regulations by creating a solenoid that would disable the EGR shortly after the engine was started. Pontiac engineers learned the Environmental Protection Agency’s EGR test lasted 50 seconds so they designed the solenoid to shut down the EGR after 53 seconds. Unfortunately, the EPA got wise to Pontiac’s mischief and necessitated the removal of the solenoid. In order to determine this action had been performed, the EPA instructed that the engines be painted a slightly different color so the inspectors could easily recognize them.
It’s a wonder the engine was ever created at all. Pontiac brass almost killed the Super Duty entirely. Pontiac sales literature from 1973 stated the Super Duty would be optional on several Pontiac models, including the Firebird. Since the Firebird and Trans Am were Pontiac’s premier sports car, the Super Duty was made available only for the Firebird Formula and the Trans Am. People like John DeLorean who helped pioneer the muscle car and led Pontiac through the 1960s were long gone. It seems current Pontiac management weren’t exactly keen on muscle cars any more.
Identifying a Super Duty-equipped Firebird or Trans Am is fairly simple. Just looked for the SD-455 sticker on the hood scoop and and an “X “ code in the vehicle identification number (VIN). And speaking of hood scoop, 1973 was the first year the scoop was non-functional. The iconic shaker scoop has been opened up to feed fresh air into the Quadrajet carburetor. When introduced in 1970, the shaker was a functional fresh-air inlet, but Pontiac capped it off in 1973 for noise reduction. Perhaps anticipating owners’ actions, the scoop was sealed with a simple plate held in place with only a trio of easily defeated rivets. Fresh air was now breathed under the hood through a long, rubber snorkel. If you feel your engine deserves cold intake air, removing the plate is a simple task of drilling out three pop rivets
Another interesting fact is the Trans Am Super Duty was only available only in Brewster Green, Buccaneer Red, or Cameo White. 1974 brought some cosmetic changes to the Firebird and Trans Am. A new aerodynamically-shaped front end was added along with black rubber 5-mph bumpers. The rear featured new slotted taillights and black rubber 5-mph bumpers.
And just like that, the reign of the Super Duty was over. After a two-year ride, production ended at the close of the 1974 model year. With all the upheaval going on in the auto industry in the early 1970s, the Super Duty should have never happened. But it did. It just goes to show there were still some who were not ready to give up on a true muscle car at the beginning of the Malaise Era. Pontiac may be history now but the legendary performance cars they created in their time will be with us forever.
Clones have popped up from time to time, and unscrupulous sellers might not do all their research before claiming they have an original SD-455 Firebird. We’ve even seen some with the improper text on the shaker stating it was a 455 SD, clearly a seller that is not as much of an enthusiast that he expects his potential buyer to be. Our advice: If you truly want an original, expect to pay a bit more – and do your research before you drop a chunk of change on a clone. The real one’s are out there, but they’re often pricey.