 A simple "455" decal was used...  A simple "455" decal was used on the Shaker of all Trans Ams equipped with the 455 Four-Barrel Performance Package in 1976. Despite rumors that some early-year models retained the "455-HO" decals, we have yet to find any original, un-restored cars to support this. |
 Though the engine was essentially...  Though the engine was essentially the same as the standard 455 found in other models, carburetor and ignition tuning changes were employed on the WX powerplant to exploit the potential of the freer-flowing exhaust while remaining emissions-compliant. |
 The Borg-Warner Super T10,...  The Borg-Warner Super T10, four-speed manual was the only available transmission. A floor-mounted Hurst shifter was connected to it. |
 A 3.23 axle ratio was included...  A 3.23 axle ratio was included with the 455 package from either year. It was a considerable jump from the 2.41-2.56 gearing found in a typical Trans Am with a 400ci engine and automatic transmission. When combined with the Super T10, the 3.23 gearset accented the 455's low torque peak to maximize acceleration yet maintain moderate engine speeds while cruising on the highway. |
 A specifically tuned, transverse-mount...  A specifically tuned, transverse-mount muffler was included with the 455 package from either year. Chromed exhaust splitters were specific to the 455 H.O. package for 1975 but standard on all Trans Am models in 1976. |
While it may first appear that the 455 H.O. package was geared entirely toward acceleration, a set of semimetallic front brake pads otherwise found in police packages were included to reduce brake fade. These pads were used in conjunction with a specific combination valve for smoother braking action. Vintage tests indicate that panic braking from 60 mph required only 180 feet to come to a full rest. However, due to concerns that not all cars were being assembled with the correct combination valve, a warranty recall was issued for the 455 H.O. Trans Ams to ensure each had received the proper valve.
The package was carried over for the '76 model year. It was, however, renamed "455 Four-Barrel Performance Package" and "HO" was subsequently removed from the Shaker. List price also decreased to $125. And after thoroughly searching through factory sales literature and service documents, it appears that the semimetallic brake pads were eliminated, ultimately leading to the $25 reduction. In addition, every Trans Am for 1976 received the chrome splitters, but only those with the 455 Four-Barrel Performance Package had the specifically tuned muffler.
Performance
The lackluster performance of the '75 400-powered cars had magazine writers nervously awaiting their chance to drive a 455 H.O. Trans Am. But since production did not begin until late-year, few magazines had the opportunity to test the Sterling Silver press car. Performance proved only marginally better than its 400ci counterpart, with quarter-mile times in the low-16-second range and trap speeds around 88 mph. Various comments made by the authors, however, indicated that a combination of harsh testing and poor tuning contributed to its meager performance.
Although the drivetrain was unchanged for 1976, performance noticeably improved. The two press cars-one Carousel Red and the other Sterling Silver-accelerated from 0 to 60 mph in about 8 seconds, with quarter-mile times in the mid-15s and trap speeds in excess of 90 mph, which is a much more realistic performance representation. Though not staggering by today's standards, these 2-ton pieces of American iron still held the potential for respectable performance. And with only a few modifications, some of that hidden horsepower could be unleashed.
In its May '76 issue, Cars magazine placed Pontiac performance legend Nunzi Romano of Nunzi's Automotive in Brooklyn, New York, behind the wheel of the Sterling Silver '76 press car. After establishing a baseline, Romano adjusted the tire pressures, opened the hoodscoop, and removed the air filter. These simple modifications reduced quarter-mile time to 15.07 while trap speed increased to 93 mph. Romano then removed the head pipes from the manifolds to bypass the catalytic converter and followed up with an astounding 14.71 at a speed in excess of 98 mph. The article also stated that additional modifications were planned and that the results would appear in the June issue. But readers saw no more.
During a recent conversation with Romano, we asked if he recalled modifying the car for a follow-up article. He said that after the initial test, Ram-Air exhaust manifolds, a true dual exhaust system, higher-ratio rocker arms, and 3.73 gears were installed. The carburetor and distributor were also modified accordingly and the smog equipment was disabled. He stated that performance dramatically improved and that it felt much like an earlier model on the street. But while driving the car to the track for the second round of testing, Romano was rear-ended while waiting at a stoplight, and the car was totaled. No subsequent testing was ever performed.
Conclusion
Not considered a vintage musclecar in the traditional sense, the '75-'76 455-powered Trans Ams became nothing more than used late-models within a few years of their release. As popularity of the W72 400ci soared in the late '70s, many were literally driven to death and unceremoniously parted out or crushed after their tenure. This left few of the 8,439 cars produced in an unmolested state. Most were driven hard or modified, and many are without their numbers-matching drivetrain, yet they remain restorable and offer many miles of driving enjoyment.
As the trend to restore the mid-to-late-'70s Firebirds increases, so does the availability of restoration parts. Once overlooked by many, only now are the '75-'76 455-powered Trans Ams being recognized as affordable, big-cube, restoration candidates. So before writing one off as a low-performance, smog-era vehicle, take a moment and realize how much potential these 455-powered Trans Ams offer. You might just find that the 455 H.O. and 455 four-barrel Perform-ance Packages contain everything you want in your next project.