|Production||Color & Trim||Engines||KwikSpecs|
If 1973 is remembered for anything in the automobile industry, it has to be the Arab Oil Embargo. The Arab nations, upset at the world for the exploitation of their country, decided in unity to low the flow of oil to raise their prices. People suddenly realized that 35-cent a gallon gasoline and 10 miles per gallon wasn't a bad thing, but take the same 10-mpg and charge 70-cents for the same gasoline... Toyota and Datsun were a guaranteed success overnight. But ask a car guy what 1973 really meant and they'll probably announce two terms - Super Duty and the "screaming chicken".
For the first time since 1970, two engines were offered in the 1973 Trans Am, both displacing 455 cubic inches, in base and Super Duty versions. The engines might have offered the same displacement, but that is where the similarity ended. The base engine (coded as follows - manual WT, WW, ZZ, and, ZE and for the automatics - X7, XE, XL, XM, YA, YC, and YD) produced 50 fewer horsepower than their round ported 1972 H.O. counterpart. Horsepower was 250@4000 rpm while peak torque took a hit as well, dropping to 370 lb/ft @2800 rpm. Increased emission regulations meant a drop in the compression ratio, now down to 8.0:1. The output of oxides of nitrogen (large displacement engines are more succeptable to high levels of N0x as compression ratio's increase) were lessened with a lower compression ratio. Pontiac removed the H.O. designation from the engine, and simply badged the shaker with 455 engine calouts.
The cylinder heads topping the motor were again of a new casting number, the 4X. This cylinder head was also used on the 400 engine available on other Firebirds. Actuating the 2.11" intake valves was a camshaft with .410" of intake and .414" of exhaust lift. Although the lift figures are still respectable, the duration of the cam was hacked off to 273 degrees on the intake cycle and 289 degrees for the exhaust. As if the shorter duration of the cam was not enough to drop power, the exhaust valves shrunk to 1.66 inches of head diameter. This valve size is reserved for small blocks, not 455 CID Trans Am motors! The engine was topped with a cast iron manifold on which a Rochester 4-barrel carburetor sat.
The name Super Duty brings back memories of the famed lightweight Catalina drag cars of the early sixties. Armed with beefy horsepower producing engine internals and lightweight aluminum body parts, the Super Duty's were race cars with lights and license tags. When Pontiac decided to turn loose a modern version of a race car motor for the street, tagging the engine with the Super Duty moniker was a natural. As smog motors go, until the advent of the wonderful computer controlled engines we enjoy today, this was one of the most powerful engines produced. Sure Chevrolet put L88's & ZL1's in Corvettes, Chrysler did some "Street Hemi's" and Ford built the 427 side oiler and OHC 429's; but these engines were spawned in a different era. The concept of "Win on Sunday and Sell on Monday" was all but dead. Pontiac engineers kept the faith. The Super Duty was an engine that for all intents and purposes, should never had seen the light of day, but on March 15, 1973, permission was given to release the engine into production cars. The purpose built cylinder heads, engine block, wildly aggressive camshaft profile, and power figures of 290 net horsepower at 4000 rpm and 395 lb/ft of torque at 3600 rpm certainly did not fit the moods of the times.
At the June 28, 1972 long lead press preview at GM's Milford Proving Grounds, Herb Adams, who headed the chief of Pontiac's Special Products Group, announced that Pontiac would be producing a Super Duty version of the 455 engine. This engine was slated to be available in the Firebird, LeMans, and Grand Am lines for 1973. The engines would be rated at 310 net horsepower and would be available in the September timeframe.
Well, it appears that Pontiac had to play games to get the Super Duty a smog legal status. Originally, a camshaft with .480" inches of lift was planned and indeed this engine seemingly passed the emissions tests, as the duration of the tests lasted 50 seconds. Pontiac developed an EGR system that would only be activated for 53 seconds of run time, enough of a cushion to allow for production variances. The EPA found out and decided this little variation wasn't quite in the spirit of the law so the approval was revoked and Pontiac set out to re-engineer the SD so it would be legal again. Carburetion changes were required, but the biggest "take-away" was a new camshaft, now limited to .410" of valve lift. Not quite what had been promised, losing 20 horsepower, but Pontiac could have easily given up on the whole project, and the Trans Am world would have been without one of the greatest supercars of all times. As a result of the recertification process, deliveres of the SD-455's were held until April of 1973.
Super Duty engines were coded ZJ and W8 for manuals and XD and Y8 for automatics. Starting at the bottom of the engine let's talk about the block. The engine block used to build the SD was significantly reinforced with additional webbing in the main bearing and lifter bore areas for strength. The main bearing caps were of mallable iron instead of ductile iron as on other engines for increased strength, and utilized the preferred four bolt arrangement. Resting in the mains was a nodular cast iron crankshaft which was rolled and filleted for better oiling and less friction. A forged crank was preferred by all involved, until they realized this single piece would nearly double the production costs. Since in production form the engine did not have high compression and caried a 5700 rpm redline, a tougher forged crank really wasn't needed. The block did have a reinforced boss at the cam drive so that a racing style dry sump oiling system could be fitted.
Where the H.O. engines were line assembled using select parts, the Super Duty engines were all hand assembled. All pieces were carefully weighed, measured, and fit to the exacting tolerances required. At the rear of the block on all other engines except the 1973 SD's is a transfer lug which is used to move the blocks into position on the assembly ine. This lug was not need and therefor removed on the '73 Super Dutys.
Speaking of lubrication, an 80 psi oil pump replaced the 60 psi unit in the standard 455. To handle the increased oil pressure, screw in oil plugs were fitted in place of the standard practice of press fitting the plugs. To keep the oil in the bottom of the pan and away from the crankshaft, a baffle was added. This added to the stability of the oiling system by reducing foaming at high rpm. The oil pump was driven by a SD-only distributor arrangement which was mounted in a sleeve which made up the 3/8" difference between the standard distributor mount and the enlarged mounting hole specific to the SD block.
Piston's chosen to fit within the SD-455 engine were a flat top with full width valve releif pockets made by TRW and were forged aluminum as opposed cast for additional strength. Forged connecting rods of 5140 steel chosen were shot peened and magnafluxed for durability and were held in place with larger heavy duty 7/16-inch (vs. 3/8") rod bolts. The procedure for attaching the piston to the rod used a heat inserted pin rather than pressing the pin which is common practice for production engines.
Now for the cylinder heads, the single component that made the Super Duty horsepower. In an effort to build a killer street engine, Pontiac knew that the current emissions legal cylinder heads would not do. What they needed was a Ram Air IV style head, only better. The engineers with the help of the Air Flow Research company succeed. This new head utilized a new technology in cylinder head casting, that was to add steel pushrod tubes into the castings to allow for thinner walls and better flow. By substituting these tubes which had a .030" wall thickness (instead of a .180inch casting thisckness), significant improvement in airflow was achived. These tubes actually broke thru the enlarged port walls. This size of the reduction in pushrod wall thickness may seem a small and insignificant number on paper, but when you consider this hungry engine ingested 2500 pulses of air and fuel each minute, the details count.
Once the air left the cylinder heads, it had to find a way into the combustion chambers, so the valves too were reworked. The valves chosen for service in the SD were back to normal size - 2.11/1.77 -inches for intake and exhaust valves. Both used longer stems, owing to the increase in lift. Special procedures prepped the intake valves as the were swirl polished for maximum air flow. The exhaust valves were not ignored either as the were comprised of Inconel 751, a high strength, high temperature steel alloy originally developed for jet engine turbine blades. Iconel material was chosen because of the higher combustion temperatures due to leaner fuel mixtures. Valve seats were cut at a 45-degree angle rather than the customary 30-degree angle of the more docile engines. The combustion chamber volume for these heads were 111 cc's.
Although the engineer designed a wonderful cast aluminum intake manifold to top the SD-455, a cast iron version was released on production versions. It seem the aluminum intake could not offer the stable cold driveability or emissions compliance GM required. The EPA guys won this one. One again a Rochester 4MV four barrel carburetor was chosen, but this one was rated at 800 cfm. Helping the fuel to exit the engine was a pair of specific cast iron header-like exhaust manifolds. The manifolds offered good flow and mated up to the round exhaust ports. The exhaust was sent the rest of the was back through a pair of 2 1/4 inch exhaust pipes and dual resonators.
On the outside, the shaker hood scoop was merely a reminder of what was; it still shook but no longer scooped. Changes in external noise regulations took away the solenoid actuated flapper and replaced it with a permanently sealed block off plate. Did I say permamently? Perhaps this should be rephrased because as soon as these cars were shown to the press, they had in print just how easy it would be to merely drill out three rivets and pitch the plate. The air cleaner now had to rely on cold air being picked up by a hose whose opening was tucked away behind the left front fender. Fear not as on a hot day, this colder air could be worth 15 to 20 horsepower
Super Duty engines had a choice of transmissions: the near bullet proof Turbohydramatic 400 three-speed automatic or the famous Muncie "rock crusher" close ratio four-speed manual with a Hurst shifter. Either transmission was mated to a limited slip rear axle with a 3.42 ratio when ordered without air conditioning and a 3.08 gear when equipped with air conditioning An automatic version was capable of propelling the T/A down the quarter mile in 13.54 seconds at 104.29 miles per hour as reported in Hot Rod magazine in the June 1973 issue*. It wasn't until the advent of the $60,000 Corvette ZR1 seventeen years later that a domestic car could realize those numbers.
Inside the Trans Am used the same Morokide high back bucket seats as standard equipment. The optional custom trim was all new as it featured new seat coverings and door trim panels. The custom interior took on less of the sporty appeal as the base seats, trading for a more luxurious look. The door panels with custom trim introduced to the Trans Am a softer image and the seats were much more flat and had a smoother finish. The door panels did away with the vertical pleats and took on an overstuffed character. The T/A was catering to a changing audience.
As for the music that was not generated by Trans Am's free flowing dual exhausts, buyers had one fewer choice. The cassette tape player, not catching on, was removed from the option list. Eight-track was still king and the cassette would stay out of the option book until 1978.
On the outside much was changed, but let's talk about what you didn't really see. For 1973, the government imposed new standards requiring 5-mph bumpers in the front, and 2.5-mph bumpers in the back. At the time, these were just devices that paid lip service to the insurance industry, and quite frankly turned many a good looking car into hideous beast in one fell swoop. The idea was to do away with the cosmetic bumper that many cars were featuring and adding a bumper that could sustain a mild "bump" (clever terminology) and not show any damage.
It was this new standard and a poor sales performance by the "pony" cars that nearly eliminated a Firebird from the Pontiac lineup. GM was not about to invest potentially millions of dollars redesigning a lame duck car, so the engineers had to come up with a was to modify the current car to meet the new standards without any major tooling. Pontiac engineers found a way to brace the energy absorbing endura front bumper into the engine compartment and lower subframe, eliminating load from the easily bendable front fender to pass the tests. Helping the endura bumper to live up to it's namesake, the center area had a steel reinforcement which was covered by four inches of deformable urethane foam. In the rear, stronger rear bumper braces completed the task. 1973 was the last year for chrome rear bumper and the "small" tail lamps.
Now for what you can see...how about red, green, and white? Two new colors supplemented Cameo White on the '73 T/A, Buccaneer Red and Brewster Green, while Lucerne Blue was eliminated. Of the colors, the Buccaneer Red seemed to be the most photogenic. Pick up any car magazine of the period or attend a car show, and most likely you will find a red car. Second in popularity seems to be the white, while Brewster Green was the elusive one, and perhaps the most desired today.
Color was only a small part of the exterior story for '73. The traditional nose bird was given a new, more wildly detailed look. The bird grew larger wings and a much more fiery look. The new bird looked great , but is was the big bird that spit fire in front of the shaker and wrapped it's might wings around it. This was the RPO WW7 Hood Decal, and option exclusive to Trans Ams. Talk about awesome. Sure it's neat to see a '73 with a clean hood and the small bird affixed to the front bumper, but deep down, we all want the big bird!. It is doubtful if designers John Schinella and Bill Davis could have imagined the visual statement that his $55 option announced. Was it gaudy? Perhaps. Was it too loud? Pretty much. Was it really necessary? Absolutely!
The big bird (or by it's affectionate nickname, the screaming chicken ) took on a different hue depending on exterior color. On Cameo white cars, it was a black bird with blue highlights. If Brewster Green was chosen, again a black bird, but this time with green "flames". The black bird got a red-orange flaming wings when ordered on a Buccaneer red car. The Trans Am decals were a bit larger than the '70-'72 versions, and were given the same accent color schemes as the wing's flames per color of choice.
The shaker engine callout decals leave a bit in question. Many of the magazines from the period illustrate super duty 455 cars, but without the SD preceding the 455 on the shaker. It is generally accepted that all engine callouts were black on red cars, blue on whites, and a lighter shade of green on Brewster Green cars.
When it came to the chassis, Pontiac introduced "Radial Tuned Suspension" to the world. When ordered, it included the GR70-15 radial tires replacing the F60-15 bias ply raised white letter tires. RTS delivered a much more comfortable ride, while providing cornering grip nearly on par with the bias tires. Radial tires, still in their infancy for American cars, were unable to match the cornering power of the very developed non-radials of the day. As the radials has a more compliant sidewall, reducing the rear roll stiffness was allowed and RTS cars did come through with a smaller rear stabilizer bar. The radial revolution was upon us, but why, oh why, did you have to do it with whitewalls?
How Pontiac divided up T/A production follows; 250 hp 455 with an automatic - 3130, same motor but with a 4-speed - 1420. Super Duty cars were much more rare, with only 252 examples being assembled. One-hundred-eighty were coupled to the smooth shifting Turbohydramatic 400 and the remaining seventy-two SD-455's were matched up with the rock crushers.
All told, 1973 was a very good Trans Am year. You had the best production engine, the best styled, and the best sales to date. In total, 4,772 Trans Am's were built, almost a four fold increase over 1972's performance. Perhaps it was because Trans Am was now the only game in town. Cuda's and Challenger's were cut down to mere a 240 horsepower 340 V8 as their weapon. Mustang, got big, heavy, and sluggish, with the 4-barrel 248-hp 351 engine as the top offering. As for T/A's little sister, the Z28, the 245hp detuned Corvette 350 V8 was as good as it got.
The 1973 T/A proved that when the engineers run the asylum, excellence and creativity can prevail. But in the early seventies, performance was a bad word, and tough time were ahead for the mighty bird.
455 - Base
Total 455 - Base
Total 455 SD
Total Trans Am
|Exterior Colors||Code||Interior Colors||Std Trim||Code||Custom Trim||Code|
||Beige||Cloth & Morokide ||551
CID - Version
455 - Base
WT, WW, ZZ, ZE
455 - Base
X7, XE, XL, XM, YA, YC, YD
4-Manual Wide Ratio
4-Manual Close Ratio
All w/ Air Cond
SD 455 wo/ Air Cond
SD 455 wo/ Air Cond