The 1971 Mustang Mach 1 came only on the “SportsRoof” fastback body style. All first generation Mach 1’s are distinguished by the body style code 63C on the door data plate. The Mach 1 also got other visual and performance enhancing items such as matte black hood treatment with hood pins, hood scoop (including optional Shaker scoop), competition suspension, chrome pop-open gas cap, revised wheels with Goodyear Polyglas tires, chrome exhaust tips (except 351W 2V), deluxe interior, livery and dealer optional chin spoiler, rear deck spoiler, and rear window louvers (SportSlats).
The Mach 1 for 1971 used a different grille/bumper combination than the regular base Mustang. The Mach 1 honeycomb grille housed two driving lamps while the front bumper was covered with urethane color-keyed to the Mustang’s paint. Fender moldings were also color keyed. The non functional NASA hood was standard equipment. The hood along with the lower body were painted either black or argent, depending on body paint. Color keyed dual racing mirrors were standard and all Mach 1s came with front fender Mach 1 decals. There was also a small Mach 1 decal on the rear deck above the pop-open gas cap. Boss 351 type side stripes were optional.
In the interior, the Mach 1 came standard with the base Mustang interior. Optional was the Mach 1 Sports Interior, which was optional on other Mustang SportsRoof models as well. Besides the special seats, door panels, 2-spoke steering wheel and clock, the package included the instrumentation group which consisted of three additional gauges- oil pressure, alternator and water temperature, all housed in a panel above the radio.
Standard engine with the Mach 1 was the 302 V-8, and all other V-8 were optional, except the 330 hp 351 found on the Boss 351. Optional V-8s were the 240 hp 351 V-8, the 285 hp 351 V-8 and the 370/375 hp 429 V-8. All 351 V-8s were of the Cleveland engine family. In May 1971, a low compression 280hp 351 V-8, called the 351CJ, replaced the 285 hp 351 V-8 that was available at the beginning of the model year. Both of these 351s had the same engine code, M.
The 428CJ was replaced by the 429CJ as the top Mustang and Mach 1 engine. The 429 belonged to the Ford 385 Engine Series and as such, no parts were interchangeable with the older 428. Wider, larger, and heavier, the 429 would not readily fit into the 1970 Mustang engine compartment, which is one of the reasons why the 1971 Mustang got bigger. The cylinder block was a variation of the 429/460 block, of which the Boss 429 was also based on; the cylinder heads were similar to the 351 Cleveland in design. You could describe the 429 as a large Boss 302. As equipped in the Mustang, the 429CJ came with four-bolt mains, forged rods and pistons, 11.3:1 compression ratio, a hydraulic cam, (similar to the Boss 429’s) very large ports and valves, and all 429CJs came with aluminum valve covers. The 429CJ came with a Rochester Quadrajet four-barrel carburetor, and some early units had adjustable valve trains.
The 429CJ became a 429SCJ if the Drag Pack option was ordered. It consisted of a 3.91 or 4.30 rear axle ratio with Traction Lock or a 4.11 ratio with a Detroit Locker rear. Both of these engines have the engine code C. Some Mustangs with the Drag Pack also included an external engine oil cooler, though of a different design than previously used. The SCJ engine came with a Holley 780 cfm carburetor rather than the Rochester Quadrajet, a mechanical lifter camshaft and adjustable rocker arms.
Although the 429s were available on any Mustang body style, the big engine was most often seen in the Mach 1, which was still the main Mustang performance model.
1,865 429CJ equipped Mustangs were built in 1971, most being Mach 1s.