Though it was more or less a humble Falcon beneath its sporty skin, Ford's new Mustang still looked like nothing ever seen before when it burst onto the scene in April 1964. More than 417,000 were sold within a year, a new Detroit record. Bucket seats and a floor shifter were standard, and either six-cylinder or 289-cid V-8 power was available under that long hood. Ford's K-code High Performance 289, rated at 271 horsepower, remained the hottest optional engine up through 1966.

Unveiled right after the so-called “1964½” run morphed into the traditional 1965 model year, the even sportier 2+2 fastback pushed the Mustang's body count to three, joining the carryover coupe and convertible. Another choice offered in all three shapes, the Mustang GT, debuted in April 1965 to help mark the first birthday of a new genre called the “pony car”. Various details set a 1965 Mustang apart from its 1964½ predecessor. The easiest to remember was Ford's switch from archaic generator to a modern alternator.

Dearborn's pony car was redesigned for 1967, primarily to make more room up front for an optional big-block V-8. Though the 271-hp 289 “Hi Po” small-block remained available for one last year, it was overshadowed by the 390-cid FE-series big-block, rated at 320 horsepower. Also new for 1967 was the “GTA,” an automatic transmission variation on the continuing GT theme. The GT/GTA segregation was enacted for one year only. All were simply called GTs again, regardless of transmission choice, in 1968.

Making more headlines in April 1968 was Ford's announcement of a new engine option. The 335-hp 428 Cobra Jet V-8 was a big-block bully that vaulted the Mustang to the forefront of Detroit's muscle car race. Hot Rod magazine called the '68½ CJ Mustang “the fastest regular production sedan ever built.” Available as a coupe, fastback or convertible, the venomous 428 Cobra Jet Mustang was available through 1970.

Ford unveiled another restyle in 1969, but it was lost in the shadows of three new models: the Mach 1, Boss 302 and Boss 429. Various competition-style appearance items and the GT-handling suspension were standard for the Mach 1, with engine options including the 351-cid small-block, 390 big-block or 428 Cobra Jet. Two race-ready Boss V-8s, the 302-cid small block and 429-cid big block were predictably the hearts of other two hot-to-trot pony cars. The Boss 302 produced 290 horsepower, and its 429 cube big brother made 375 horses.

Handling was the main strength of the Boss 302, which was created to take on Chevrolet's Z/28 Camaro on SCCA Trans-Am road courses. The idea behind the big, bad Boss 429 involved homologating its exotic V-8 for NASCAR tracks, where it did its darndest beneath mid-sized Talladega hoods. Both Boss Mustangs were built through 1970. Boss 302 production was 1,628 in 1969 and 7,013 in 1970. Boss 429 numbers were 857 in 1969 and 499 in 1970.

Purists who were annoyed at the enlarged 1967 Mustang had another thing coming when Dearborn's truly large 1971 redesign appeared. Wheelbase went up an inch, overall length increased 2.1 inches, and weight ballooned by nearly 200 pounds. Under short-term Ford president Bunkie Knudsen's direction, Ford's pony car was expanded once more to make even more room up front for even more engine. New on the options list in 1971 was the 385-series big-block V-8, displacing 429 cubic inches. Advertised output for the new 429 Cobra Jet was 370 horsepower, with or without optional ram-air induction.

The sporty Mach 1 carried over, again only in fastback “SportsRoof” form, but the Boss 302 and 429 didn't. They were instead followed by the Boss 351, a 330-hp SportsRoof built for 1971 only. Boss 351 production was 1,806.

The Mach 1 remained the Mustang's flagship through 1973. Other models of note included the patriotic Sprint hardtops and SportRoofs built only for 1972, and that year's “Olympic Sprint” convertibles.