While maintaining a basic resemblance to previous Mustangs, the 1971 Mustangs were the largest and heaviest yet. Every dimension increased; Wheelbase was stretched to 109 inches.
Engine choice still remained high; a total of ten different engines were available on the 1971 Mastang.
Base engine was the 250 ci six-cylinder on all models except the Mach 1 which came with the 210 hp 302 and the Boss 351 which got a 330 hp version of the 351.
Optional V-8s were the 210 hp 3O2, 240 hp 351, 285 hp 351, 370 hp 429 and 375 hp 429. All 351 V-8s were 35lCs. In May 1971, a low-comprewion 351 CJ replaced the 285 hp 351 that was available at the beginning of the model year, rated at 280 hp. Both of these 351s had the same engine code, M.
The 428CJ was replaced by the 429CJ as the top Mustang engine option. The 429 belonged to the 385 Engine Series and as such, no parts were interchangeable with the 428. Wider, larger and heavier, the 429 would not readily with into the 1970 Mustang engine compartment, which is one of the reasons that the 1971 Mustang got bigger. The bottom end and cylinder block wen a variation of the 429/460 block, on which the Boss 429 was also based. 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, 2.25 inch intake and 1.72 inch exhausts. Regular production 429/460 engines came with cylinder heads that had smaller ports and valves. The 429CJ came with a Rochester Quadrajet four-barrel carburetor, and some early units had adjustable valve trains. All 429CJs came with aluminum valve covers.
The 429CJ became a 429SCJ if the Drag Pack option was ordered. It consisted of a 3.91:1 or 4.30:1 rear axle ratio with Traction-Lok or a 4.1 1:1 ratio with a Detroit Rocker rear. Both of these engines had 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 780cfm carburetor rather than the Rochester Quadrajet, a mechanical lifter camshaft and adjustable rocker arms.
Mustangs equipped with the 429CJ Ram Air engine got the letter J for the engine code in the VIN. It was rated at 375 hp. The 429CJ-R engine could either be a CJ or SCJ, if it had the Drag Pack option or not. The Dual Ram Induction option consisted of a hood with two functional NASA-type hood scoops, which were controlled by engine vacuum.
All four-speed manual transmissions came with a Hurst shifter.
The Competition Suspension, available only on Mustangs with 351-2V engines and larger, consisted of heavier-duty shock absorbers, springs and front and rear stabilizer bars (rear bars for 351 four-barrel and larger engines only), and staggered rear shocks (except for the 351-2V engine). Mustangs with this option got power steering with variable ratio. The Competition Suspension was also mandatory with the optional 15x7 chrome Magnum 500 wheels.
Twist-type hood locks, a Tu-tone paint treatment, black or ugent, and Ram Air decals rounded out the option. It was available only on 351 and larger engines.
The optional variable ratio steering had a 15.7:1 ratio.
While the rear deck spoiler remained on the option list, the Sport Slats were deleted, due to the low angle of the SportsRoofs rear window.
For the first time, power windows and an electric rear window defroster were optional. The electric defroster was not available on convertible.
The four-pod instrument panel of 1969-70 was replaced by a three-pod design. Two large pods with a smaller one in between them dominated the driver's side of the dash. The large left pod consisted of four warning lights: oil pmmure, temperature, brakes and alternator. The center pod was for fuel while the large right unit housed the speedometer.
The optional instrumentation group (standard on the Boss 351 and not available with the 250 ci six-cylinder) consisted of three instruments, oil pressure, alternator and temperature, housed in a panel located above the radio. The warning lights on the left large pod were displaced by an 8000 rpm tachometer.
The three-spoke Rim Blow steering wheel was optional. Similar to the one used on 1969-70 Mustangs, it used a redesigned center pad. The tilt steering is optional; however, power steering was a mandatory option.
The Decor Group (not available on the Mach I or Grande) consisted of either knitted vinyl or cloth inserts for the seats, black instrument panel faces, the deluxe two-spoke steering what molded door panels (available only on the convertible and Boss 351), rear ashtray, dual color-keyed racing mirrors, and rocker panel and wheel lip moldings. The moldings were not available with the Boss 351.
The Mach 1 Sports Interior, available on the Mach I and all other SportsRoofs, consisted of knitted vinyl seats, the two-spoke deluxe steering wheel molded door panels, black dash panel applique, woodgrain applique for the center instrument panel, rear ashtray, electric clock, the instrumentation group, bright pedal pads, and color-keyed rubber floor mats stitched directly on the carpets (front only).
The fold-down rear seat option included a Space-saver spare tire.
The Mach I for 1971 used a different grille-bumper combination. The 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 NASA hood was standard equipment (non-functional). 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 I decals.
There was also a small Mach 1 decal on the rear deck above the pop-open gas cap.
Boss 351 side stripes were optional.
Standard engine with the Mach 1 was the 302 V-8, and all other V-8s were optional, except the 330 hp 351 found on the Boss 351.
The Boss 351 replaced the Boss 302 and the Boss 429 as the premier performance Mustang. Like previous Boss Mustangs, it was a complete package, with limited options.
Standard was the 330 hp 351 Cleveland featuring a four-bolt main block, large port cylinder heads and valves, a wild lifter camshaft, an 11.7:1 compression ratio and aluminum valve covers.
Other standard features were Ram Air, 3.91:1 rear axle with Traction-Lok, four-speed manual transmission, Competition Suspension, power front disc brakes, front spoiler, the Mach 1 front grille and lower body side paint treatment, bodyside tape treatment and Boss 351 decals in place of the Mach I decals.
The Boss 351, however, came with the standard chrome front bumper. The hood differed from the Mach l's as the black or argent paint covered most of the hood.
Standard wheels on the Boss 351 were 15x7 with trim rings/ hubcaps. Optional were the l5x7 chrome Magnum 500s. Tires in both cases were Goodyear F60xl5 RWL.
The Grande was still promoted as the luxury Mustang, available only on the hardtop body style. A full vinyl roof, Grande lettering on the "C" pillar, dual accent paint stripe, color-keyed racing mirrors, bright rocker panel and wheel lip moldings, and special Grande wheel covers were all standard equipment on the exterior. In the interior, the Grande came with the Deluxe two- spoke steering wheel, black dash panel appliques, woodgrain applique in the center dash, molded door panels, Lambeth cloth seat inserts, electric clock rear ashtray and bright trim on the pedals. All 1971 Mustang engines were available on the Grande.
Further watering down the overall performance image of the Mach I and Boss 351 Mustangs was the availability of the Sports Hardtop option late in the model year. Based on the hardtop body, it used the Mach I's honeycomb grille and color-keyed bumper, the standard Mach 1 hubcap/trim rings, the non-functional NASA hood and the Boss 351's side stripes.