It is unlikely that you will encounter many 1973 Pontiac GTOs in the wild.
They exist, though in small numbers. During a turbulent year in U.S. history, fewer than 5,000 Colonnade-body GTOs arrived in dealerships. As federal rules began to affect automobiles, energy-absorbing bumpers were added as an afterthought, and pollution requirements crippled engines that were formerly renowned for their tremendous horsepower. In the midst of it all, and perhaps not surprisingly, Pontiac scarcely promoted the 1973 GTO, a model that had been a pioneer in the 1960s muscle-car era. Instead, the division allocated marketing funds to the European-inspired Grand Am, the GTO's new alter ego.
Compared to 1964-1972 GTOs, 1973 models are less expensive and have more limited availability of replacement components. These are not vehicles to purchase and resell for a profit or to restore and sell for a profit. Consider the 1973 GTO if you want to be part of the GTO brotherhood while driving a rare collector vehicle.
1973 Pontiac GTO purchasers may choose between two V-8 engines: the basic 400-cu.-in. L78-code engine with 230 horsepower or the optional 455-cu.-in. L75-code "D-port" V-8 with 250 horsepower. Less than 600 original 455 automobiles were manufactured, making them prized today.
It is reasonable to conclude that the Pontiac 400 and 455 V-8 engines were overbuilt for normal daily driver use, especially when they were under stress as they were in these vehicles mileage, age, and neglectful care may take their toll, but these V-8s are simple and very inexpensive to rebuild, and there is a broad selection of high-performance parts available if additional horsepower and torque are essential.
To maintain at least a semblance of performance, the Pontiac engineering department devised an induction system inspired in part by early American aeronautics. The initial intent of NACA ducts was to draw air into a jet engine without causing resistance or turbulence. What worked for aircraft may also work for automobiles, therefore Pontiac incorporated two NACA vents onto the 1973 GTO hood. Air was intended to flow via the NACA ducts and be compelled into the carburetor via ductwork.
The basic L78 400 was available with a selection of transmissions: a Muncie heavy-duty three-speed manual, a Muncie four-speed manual, or a Turbo Hydra-Matic 400 automatic. Instead of a Hurst package, both manual transmissions were equipped with an Inland shifter and linkage. Only the GM Turbo Hydra-Matic 400 three-speed automatic transmission was available for 455-equipped vehicles.
The Turbo 400 is a bulletproof transmission that is more than up to the task of powering a factory 1973 GTO. When properly constructed, it can also accommodate the maximum amount of horsepower. If you're fortunate enough to acquire a four-speed manual vehicle, Muncie's four-speeds are inexpensive and simple to maintain. The same applies to the heavy-duty three-speed manual. You would assume that vehicles with three speeds would be exceedingly rare, but they exist.
Safe-T-Track limited-slip was offered for an additional fee. While GM performance aficionados tend toward the 8.75-inch 12-bolt rear axle, the 8.5-inch 10-bolt is a durable axle that can last hundreds of thousands of miles and can be designed to resist drag strips pinstriping. Rear-mounted gear ratios included a 3.42:1, a conventional 3.23:1, and an Interstate-friendly 3.08:1. The only rear axle used under these GTOs was a GM 8.5-inch 10-bolt axle, which was shared with Chevrolet, Oldsmobile, and Buick.
In 1972, the Pontiac GTO came standard with manual drum brakes, but for 1973, the base package incorporated power-assisted 11-inch front discs and 9.5-inch rear drums. Colonnades were made in great quantities, but many of their components, notably a large portion of the braking system, were shared with other GM models, so you may still find affordable replacement parts at your local auto parts store.
Two other wheel styles were also available: Rally II wheels with five spokes for the classic muscle car look, and Honeycomb wheels with a futuristic design. The Rally II and Honeycomb wheels were both 15 x 7 inches in size. Used Rally II wheels are readily available on the secondary market. 15-inch Honeycomb wheels are no longer manufactured; however, 17-inch aftermarket wheels are available.
In 1973, radial tires were fashionable, but Pontiac maintained that bias plies provided superior performance and handling. Optional raised-white-letter G60-15 tires added style but shared the same dual polyester belt and dual fiberglass tread belt design as the standard black wall tires. Uniroyal, Goodyear, and Firestone supplied the tires.
The bulk of 1973 GTOs produced were Sport Coupes with two doors. These "F37" automobiles are distinguished by the vertical louvered slats covering the rear quarter windows. Fewer than 500 slat less, two-door "D37" coupes were manufactured. The 1973 GTO's divisive style pushed it to the do-not-want list for a time, but the Colonnade is gaining supporters as time passes. Similar to older A-body GM vehicles, the rear quarters and inner fender panels on the Colonnade GTO are prone to rust, however, the rear window rust is not as prevalent due to the vehicle's sleek design and sharply sloped rear.
The Colonnade principle of shared parts and components is most evident within the building. While a handful of the components are GTO-specific, the majority of the interior is shared with the Le Mans, and many of these components were utilized during the Colonnade's 1973-1977 production cycle.