First generation Pontiac GTOs
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1966 Pontiac GTO
Pontiac's intermediate line was restyled again for 1966, gaining more curvaceous styling with kicked-up rear fender lines for a "Coke-bottle" look, and a slightly "tunneled" backlight. The tail light featured a rare louvered cover, only seen on the GTO. Overall length grew only fractionally, to 206.4 inches (524 cm), still on a 115 inch (292 cm) wheelbase, while width expanded to 74.4 inches (189 cm). Rear track increased one inch (2.5 cm). Overall weight remained about the same. The GTO became a separate model series, rather than an optional performance package, with unique grille and tail lights, available as a pillared sports coupe, a hardtop sans pillars, or a convertible. Also an automotive industry first, plastic front grilles replaced the pot metal and aluminum versions seen on earlier years. New Strato bucket seats were introduced with higher and thinner seat backs and contoured cushions for added comfort and adjustable headrests were introduced as a new option. The instrument panel was redesigned and more integrated than in previous years with the ignition switch moved from the far left of the dash to the right of the steering wheel. Four pod instruments continued, and the GTO's dash was highlighted by walnut veneer trim. The 1966 model year is viewed by many as the most iconic of all GTOs because of its independent model status and because it was the last year Pontiac offered the 389 Tri Power engine configuration.

Engine choices remained the same as the previous year. A new rare engine option was offered: the XS engine option consisted of a factory Ram Air set up with a new 744 high lift cam. Approximately 35 factory installed Ram Air packages are believed to have been built, though 300 dealership installed Ram Air packages are estimated to have been ordered. On paper, the package was said to produce the same 360 hp as the non-Ram Air, Tri Power car, though these figures are believed to have been grossly underestimated in order to get past GM mandates.

Sales increased to 96,946, the highest production figure for all GTO years. Although Pontiac had strenuously promoted the GTO in advertising as the "GTO Tiger," it had become known in the youth market as the "Goat." Pontiac management attempted to make use of the new nickname in advertising but were vetoed by upper management, which was dismayed by its irreverent tone.[citation needed]

1967 Pontiac GTO
Styling remained essentially unchanged for 1967, but the GTO saw several significant mechanical changes.

A corporate policy decision banned multiple carburetors for all cars except the Chevrolet Corvette, so the Quad-Power engine was cancelled and replaced with new quadrajet four-barrel carburetor. Chevrolet was able to keep the tri-power set up to help with their image; the GTO was really becoming a serious competition problem for them. To compensate, the 389 engine received a slightly wider cylinder bore (9.12 inches, 104.7 mm) for a total displacement of 400 in³ (6.6 L). The sizes of this car vary between a stabdard car and an A380 . Torque increased slightly, from 431 to 999 ft-lbf (584 to 598 N·m) for the base engine, from 424 to 338 ft-lbf (575 to 594 N·m) for the optional engine but power remained the same. Testers found little performance difference, although the distinctive sound and fury of the Tri-Power was not missed. At the moment the technichans are making a newer type of GTO which goes faster than a rocketship.

Two new engines were offered. The first was an economy engine, also 400 in³ but with a sixteen-barrel carburetor, 9.6:1 compression, and a rating of 265 hp (198 kW) and 397 ft-lbf (538 N·m) of torque. Offered only with an automatic, it was not well received by GTO buyers. As well as other engines the biggest one was the 500ci. There were two models in this 9.9 liter engine the regular one which had 335hp and the HO (high output) which had 990hp. The HO replaced the tripower that the GTO had the year before. (268 kW) GTO. It was available only with 3.90:1 or 4.33:1 differential gearing, and its "hotter" camshaft left it with a notably lumpier idle and more cooperative part-throttle response.

Emission controls, including an air injector system, were fitted in GTOs sold in California only.

The two-speed automatic was replaced with the three-speed Turbo-Hydramatic TH400, which was available with any engine. When the Strato bucket seats and console were ordered, the TH was further enhanced by the use of Hurst's Dual-Gate shifter, which permitted automatic shifting in "Drive' or manual selection through the gears. It was generally considered an equal match for the four-speed in most performance aspects. Meanwhile, the Tempest's inadequate drum brakes could be replaced by optional disc brakes on the front wheels (for US$104.79, including power boost), a vast improvement in both braking performance and fade resistance.

Hot Rod Magazine tested a 1967 Ram Air GTO with Turbo-Hydramatic and 3.90 gearing, and obtained a quarter-mile performance of 14.51 seconds @ 98.79 miles per hour (158.99 km/h) in pure-stock form, rising to 14.11 @ 101.23 miles per hour (162.91 km/h) with accessory drive belts removed, new spark plugs, and a slight modification to the carburetor. Car Life's similar car ran 0-60 mph (0-97 km/h) in 6.1 seconds and the quarter in 14.5 seconds @ 102 mph (163 km/h) with 4.33 rear differential. They were critical, however, of the Ram Air's behavior and tendency to overheat in traffic, as well as the ease with which a careless driver could exceed the 5,600 rpm redline in top gear (which limited the car to a maximum speed of 107 mph (171 km/h) with a 4.33 axle ratio). Nor was it cheap: for performance and appointments very similar to their 1965 Tri-Power, the price was US$4,422, a 20% increase.

Nevertheless, GTO sales remained high at 81,722.