Rare Rides: 1973 Pontiac Trans Am SD-455

The Golden Era of muscle cars, that is to say, the period between 1964 and 1971, stands as one of the most celebrated periods of American automobile manufacture.

During this time, advances in technology converged precisely with consumer demand for quicker, more powerful cars, resulting in an exponential explosion in terms of horsepower, torque, and speed over the cars of the decade that preceded it.

But as with all gilded eras, those years went by quickly, and were ultimately ephemeral.

Much more stringent federal environmental legislation, tighter insurance requirements, and an oil embargo in the early seventies conspired to force manufacturers to reduce engine displacements and compression ratios in order to comply. The once massive and hugely capable powertrains of these beloved muscle cars began to wither year upon year after 1971.

This, however, didn’t stop Pontiac, the General Motors division that many suggest created the very first muscle car in the form of the 1964 GTO, from offering a last hurrah and salute to the Golden Era in the form of an exceedingly rare and powerful vehicle: the 1973 Pontiac Trans Am SD-455.

This fabled beast, the last true, high-performance muscle car to be released for some two-and-a-half decades, is this month’s subject of Rare Rides.

The 1973 Pontiac Trans Am SD-455. (Photo courtesy of Mecum Auctions.)

The first generation Firebird, launched some five months after its F-body cousin, the Chevrolet Camaro. It was a much-needed addition to the 1967 Pontiac lineup, which lacked any sort of competitor in the pony car segment and it’s all-conquering Ford Mustang.

While it turned out not to be the sales champion of the Mustang, or the Camaro for that matter, the Firebird, with its crisp lines and more audacious appearance, nonetheless carved out a dedicated fan base in its first three years of production.

An example of the first generation Pontiac Firebird, in the form of a 1969 Trans Am. (Photo courtesy of Mecum Auctions.)

Seeking to keep the Firebird fresh, Pontiac began work on the next iteration of the car nearly immediately after the first-generation vehicles began rolling off the assembly line. The launch of the second generation Firebird, of which the 1973 model was an example, took place on February 26, 1970, after months of delays owing to labor strikes and factory tooling problems. The new car was thusly deemed a 1970 ½ model.

A familial link to the first-generation Firebird was clear in the new exterior design, but overall styling, overseen by Bill Porter, was more aggressive and less chiseled. Beginning at the front, the split grill motif was carried over, now set in a molded Endura bumper/fascia along with dual headlamps inset in square, pod-like enclosures, replacing the quads on the former car.

The bold, new lines of the 1970 ½ Pontiac Firebird Trans Am. (Photo courtesy of Steven Serge Motorcars.)

On Trans Am models, a healthy front air dam and fender skirts that preceded the front and rear wheel wells helped to shape the airflow around the car, while trapezoidal engine bay air extractors trailed the front arches. A sculpted hood with a functional, rear facing shaker scoop added simultaneous notes of sophistication and muscularity.

A curved roofline led to a sloping rear window whose angle continued onto that of the decklid. A large duckbill spoiler capped off the tail and provided a good amount of downforce, while taillights halved by a thin, horizontal, chrome strip were an evolution of the first gen’s fully split ones. Interestingly, there were no rear quarter windows present. Trans Am exterior colors in 1970 were limited to Lucerne Blue or Polar White.

The interior of a ’70 ½ Trans Am equipped with a Turbo Hydra-Matic three-speed. (Photo courtesy of Mecum Auctions.)

All Firebird trims, which consisted of the base model, the Esprit, the Formula, and the range-topping Trans Am, had well-appointed and quite sporty interiors, with bucket seats and complete headrests standard. Trans Ams were bequeathed an engine turned chrome instrument bezel, while a gauge package with a tach turned on its side like a race car was a popular option.

Lesser Firebirds had a wide variety of engine options available, ranging from a rather milquetoast 155 horsepower, 250 cubic-inch inline-six, up to an L74 Ram Air III 400 cubic-inch V8 that produced 345 ponies. The range-topping Trans Am though only had two: the L74 Ram Air III 400 cubic-inch V8, and the L67 370 horsepower Ram Air IV 400 cubic-inch V8.

The big dog for 1970 ½: the 370 horsepower L67 Ram Air IV 400 V8. (Photo courtesy of Mecum Auctions.)

Transmission choices on the base through Formula models included a column or floor-shifted three-speed manual, a four-speed floor-mounted manual, and a two-speed and three-speed Turbo Hydra-Matic automatic, with the two-speed only available on base models. Trans Am buyers could choose from the three-speed floor shifter, a robust four-speed manual with a Hurst shifter, or the three-speed Turbo Hydra-Matic slushbox.

Differentials of course depended on trim level, engine, and transmission options, and naturally, the Trans Am had the best toys, with a 12-bolt diff and up to a 3.73:1 final drive ratio with Safe-T-Track LSD on offer in four-speed cars.

The rear haunches of a ’70 ½ Trans Am in Polar White. (Photo courtesy of Mecum Auctions.)

Suspension was upgraded on the Trans Am and consisted of unequal A-arm wishbones with coil springs, telescopic shocks, and a 1.25-inch stabilizer bar up front, and a solid rear axle with parallel, semi-elliptical leaf springs, telescopic shocks, and a .875-inch stabilizer bar in the rear.

Hydraulic, power-assisted, 11-inch front ventilated discs and 9.5-inch rear drums were on hand for slowing down, and were surrounded by 15 x 7-inch Pontiac Rally II steel wheels shod with meaty, Firestone Wide Oval F60-15 tires.

The aggressive front end. (Photo courtesy of Hagerty.)

Performance of a loaded Trans Am with the Ram Air IV engine and a four-speed manual transmission was brisk, with a zero-to-sixty time of 5.2 seconds and a quarter mile taking 13.8 seconds at 102 mph.

Alas, as previously discussed, insurance and emissions concerns began to take hold after the 1970 model year, and while the 1971 and ’72 Trans Ams changed little aesthetically, with the most obvious change being the addition of the fabled “honeycomb” wheels in ’72, under the hood there were major alterations.

The ’71 (pictured here) and ’72 Trans Ams didn’t change much aesthetically, but quite a bit was different under the hood. (Photo courtesy of BringATrailer.)

Unlike other manufacturers who began to reduce the displacement of their high-performance motors to adhere to the new federal regulations, Pontiac engineers went in the opposite direction. They offset the requisite reduction in compression – which would necessitate that the ratios in the 400 drop from 10.5:1 down to 8.4:1 – by actually increasing the size of the power plants in the Trans Am.

A lone, massive engine was thusly made available in ’71 and ’72: an LS5 455 cubic-inch H.O. unit which sported round-port heads, a nodular-iron crankshaft retained by four-bolt main caps, cast ArmaSteel rods, and cast aluminum pistons. Output was 335 horsepower and a stump-pulling 480 lb-ft of torque.

The 455 cubic-inch H.O. motor from the 1971 and ’72 Trans Am. (Photo courtesy of RK Motors.)

Of note, to help Trans Am buyers afford insurance, Pontiac began using SAE net power figures, which reduced the advertised output of the 455 H.O. to 300 horses and 415 lb-ft of twist.

Another mechanical change for ’71 and ’72 was the replacement of the 12-bolt differential with a 10-bolt unit, containing a standard limited-slip 3.42 gearset for manual cars. Less aggressive 3.08 gears were used for automatics and A/C equipped cars, while the performance ratio remained a 3.73:1 cog on four-speed Trans Ams.

The 1972 Trans Am introduced the beloved “honeycomb” wheels. (Photo courtesy of Hagerty.)

Despite these changes, performance didn’t suffer too much, with the ’71 and ’72 models capable of 5.8 second zero-to-sixty sprints, and a quarter mile performance of 13.9 seconds at 101 mph.

By 1973, the muscle car Golden Era was well and truly in the rearview mirror. Performance manufacturers like Dodge and Plymouth had reduced their top engine offering in muscle cars like the Challenger and ‘Cuda to a 340 cubic-inch V8 unit capable of only 245 horsepower, a far cry from the 390 horsepower 440 six-barrels and 425 horsepower 426 Hemis of just two years prior.

The 1973 Pontiac Trans Am SD-455 in the new hue of Buccaneer Red. (Photo courtesy of Mecum Auctions.)

Pontiac, however, refused to let the glory days die for one more year, and in 1973 unleashed a Trans Am with a brute of an optional powertrain that stood as a fitting farewell to the era.

The motor in question was the LS2 SD-455 “Super-Duty” V8. Borrowing its moniker from the Pontiac high-performance engines in the early 1960s that were race ready, the SD-455 wasn’t a far cry from those motors. Essentially a street legal, race-prepped motor, the Super Duty 455 was hand assembled and had some unusual features.

The LS2 SD-455 “Super-Duty” V8. (Photo courtesy of Motorious.)

Starting down low was a cast-iron block heavily reinforced with thick bulkheads, four-bolt main bearings, and extra material in the camshaft and lifter area. 8.4:1 forged connecting rods and pistons, a nitrited iron crankshaft, and a pressure rolling operation applied to the journal fillets provided extra strength for the moving parts. An 80 psi oil system and a baffled oil pan ensured that the lubricant flowed freely all the way up to redline.

Open chambered cylinder heads were developed in conjunction with AirFlow Research, and were patterned after those in the Ram Air IV of 1970, with round exhaust ports and oversized intake valves at 45-degree seat angles. On top, a Rochester Quadrajet carb mixed air and fuel, while header-like exhaust manifolds handled the exhale.

A ’73 Super Duty in Brewster Green. (Photo courtesy of Mecum Auctions.)

Output for this lump was a vastly underrated 290 net horsepower and 395 lb-ft of torque, but these numbers were betrayed by the car’s ability to run 5.9 second zero-to-sixties and 13.9 second quarters at 101 mph straight from the factory. Most experts believe the Super Duty was actually putting out close to 375 horsepower.

A four-speed manual was standard, with the Turbo Hydra-Matic 400 an option, and both would send power to a 10-bolt axle containing a 3.42:1 or a 3.08:1 ratio respectively, with the hot optional gear continuing to be the 3.73:1.

The interior of the ’73 with the new “horse collar” seat design. (Photo courtesy of Mecum Auctions.)

Aesthetic changes to the ’73 Trans Am added to the excitement of the SD-455, and included an egg crate grille, a slightly revised front bumper, three new colors including Cameo White, Buccaneer Red, and Brewster Green, and a new “horse collar” seat design.

But perhaps the most notable addition was the debut of the “Screaming Chicken” graphic that covered nearly the entire hood, and became an iconic Trans Am signature for decades to come.

The “Screaming Chicken” was first introduced on the 1973 Trans Am and continued to be an option on the cars until the Trans Am’s demise in 2002. (Photo courtesy of Mecum Auctions.)

Horsepower wasn’t cheap in early ’70s, and the Super Duty engine added a stout $521 over the standard L75 455 H.O. unit. As such, out of the 4,802 Trans Ams built in 1973, only 252 SD-455s (72 manuals and 180 automatics) rolled out of the factory. In spite of the low sales numbers, its pizzaz as well as the enormous amount of press it generated helped to stave off the Firebird’s discontinuance, an idea that Pontiac executives had been toying with in 1972.

Naturally, with such small numbers produced, 1973 Pontiac Trans Am SD-455s are very hard to come by today, and fetch close to a quarter of a million dollars when sold at auction. Understandable money though for the sole true muscle car of the malaise era, and one of the decade’s best Rare Rides.

About the author

Rob Finkelman

Rob combined his two great passions of writing and cars; and began authoring columns for several Formula 1 racing websites and Street Muscle Magazine. He is an avid automotive enthusiast with a burgeoning collection of classic and muscle cars.
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