As SAND noted, the big difference between the 66 and 67 GTO is the engine: The 67 was the first year for the 400. '66 was the last year for multiple carbs (Tripower), and the Corvette was the only GM car that was allowed multiple carbs after '66. '67 was the first year for the 750cfm QuadraJet carb, and the H.O. 400 engine cranked out the same 360 hp rating as the 389 Tripower from '66. Along with the bigger engine came a better automatic tranny: the Powerglide 2-speed was discontinued after the '66 model year and the GTO received the Turbo 400 3-speed automatic in '67.
Changes from 71 to 72 were mostly cosmetic: The wire mesh grill from '71 was replaced by a deep-set plastic grill in '72, and the GTO received fender air extractors. 72 marked a further decrease in performance, as the standard 400 engine dropped from its 300-horse rating in '71 to 250 horse in '72. The 455 H.O. from '71 (rated at 335 horse) was continued into '72, but dropped to 300 horse. 2 of the rear axle ratios from 1971 were not continued into 1972: You could not get a 3.90:1 or a 4.33:1 Limted Slip axle in '72. In spite of lower power numbers, the 72 GTO is actually a very nice driving car: It's smooth, handles well, and it actually stops.
thx a lot guys, i asked because im planning to purchase a GTO and the ones i like are the 66' to 72' gto, as a lot of ppl.
and another thing, lars, when u said the '72 is a nice driving car, do u mean the 72 feels better to drive than the 71, despite the horsepower decrease ?
either way 66 or 67 seems like the way to go, although they can be expensive.
I've owned both 71 and 72 GTOs, and I find the 72 to be a better overall balanced car in terms of the "total feel" and refinement. It's not tough to alter the power rating with a little engine tuning and tweaking, so I wouldn't worry too much about the power drop of the '72: that just gives you something to play with to put some life in it...