The Mustang became larger and heavier with each revision, culminating with the 1971 to 1973 models designed under the supervision of Ford’s new product design manager, Semon “Bunkie” Knudsen, originally of General Motors. Introduced in September 1970 Mustang MY 1971 saw the last high-performance big-block Mustang, 375 hp (280 kW) 429 Super Cobra Jet. The body style designed for the purpose of big-block installation versions was limited to a maximum of 351 cu in (5.8 L) in 1972 and 1973 due to stricter U.S. emission control regulation, as well as the low demand for big block muscle cars because of high insurance premiums. Two more high-performance engines were introduced in 1972; the 351 “HO” and the 351 Cobra Jet. Both versions were high performers for their era, but nowhere near the level of the Boss cars and original Cobra Jet. Automakers in the U.S. switched from “gross” to “net” power and torque ratings in 1972, which coincided with the introduction of low-compression engines with different, far more restrictive induction systems. Thus, it is difficult to compare power and torque ratings.
As before there were three body styles; hardtop, sportsroof and convertible. On hardtops there was ‘Grande’ trim offered, it was meant as an luxury version. Sportsroof models were performance oriented, as it was only body version with ‘Mach 1′ option available, which was distinguishable by decals, hood with scoops (non functional in most models), color keyed; side mirrors, strip on the edge of the front fenders and hood, urethane front bumper and grille with ‘sportlights’. Cars equipped with ‘Boss’ engine had appearance of Mach 1 package, excluding front bumper, which was chrome. Convertible was equipped with a power top, a glass rear window, and tinted windshield standard. It was last Mustang available as a convertible until 1983.
Not much changed during production when it comes to exterior appearance, some details were revised however in 1973 when front chrome bumper in Base and Grande was replaced with urethane color keyed version (similar to the one sported by the 1971–1972 Mach 1) to comply with new regulations – thus turn signals were moved from underneath it to inside of the grille next to the headlights, because of those changes horizontal grille ‘sportlights’ seen in 1971–1972 Mach 1 were discontinued as new vertical blinkers took they place. Also in 1973 decals were altered with different design.
1971–1973 Mach 1 has become famous thanks to the appearances in Diamonds are Forever (1971) and Gone in 60 seconds (1974) films.
For 1972 Ford prepared special model called ‘Sprint’ it was meant to commemorate USA participation in 1972 Olympic Games. It consisted of special decals, color keyed front bumper, mirrors and grille taken from Mach 1. Performance suspension and wheels were also available.
There was no Shelby version of 1971–1973 Mustangs, save for the ‘Shelby de Mexico GT-351′, by Mexican dealer and very limited edition ‘Shelby Europa’, sold in Europe by private importer request to Shelby Motors.