71 Boss Mustang: Ford’s Overlooked Muscle Powerhouse?
The Ford 351 Cleveland engine, particularly in its Boss 351 guise, held immense performance potential that was unfortunately stifled soon after its debut by tightening emissions regulations. While Ford’s 335-series engines could have been serious contenders, only one variant truly showcased its near-uninhibited power in the North American market: the Boss 351. This potent engine was exclusive to the 71 Boss Mustang, a one-year wonder before being detuned into the 351 HO for 1972, losing its “Boss” designation as emissions controls took precedence over raw power.
When enthusiasts recount legendary muscle cars, names like Hemi Mopars, Chevelle SS, GTOs, and various Mustangs—Shelbys, Boss 302s, 428 Cobra Jets, Boss 429s—dominate the conversation. The 71 Boss Mustang is conspicuously absent from these lists, often overlooked despite its remarkable performance credentials. It consistently punched above its weight, delivering performance comparable to much larger displacement engines and standing out as one of the era’s top small-block contenders. However, its legacy is tied to the larger, heavier 1971 Mustang body style, a design that remains controversial among enthusiasts even today.
The Controversial 1971 Redesign
For the 1971 model year, the Ford Mustang underwent a significant transformation, growing in length, width, and weight to become the largest iteration up to that point. Despite these changes, it retained the underlying Falcon chassis from its 1964 origins. The aggressive, racy styling represented one of Ford’s final designs before stricter government regulations took hold, embodying the extreme performance aesthetics popular at the time.
Side profile illustration of a blue 1971 Ford Mustang highlighting its fastback styling
Often criticized as “bloated,” the 1971 Mustang’s size increase wasn’t as dramatic as its styling suggested. Compared to the 1970 model, it grew roughly 2 inches longer and 2.5 inches wider. This put it on par dimensionally with the contemporary Chevrolet Camaro and actually made it smaller than the Dodge Challenger or AMC Javelin. The perception of excessive size stemmed more from the dramatic styling cues than the actual measurements.
Under the Hood: More Than Just Looks
A key reason for the 1971 Mustang’s redesign was to accommodate Ford’s larger engines. While the 1967 update allowed the FE-series engines, the bay still wasn’t large enough for the new 385-series big blocks. The ’71 redesign solved this, creating space for the mighty 429 engine, which replaced the 428 Cobra Jet for just that single model year before being dropped for 1972.
Engine bay of a 1971 Mustang showcasing the large 429 cubic inch V8 engine
Beyond the engine bay, Ford updated the front suspension and steering. The track width was increased, suspension geometry revised, and importantly, an integral power steering system was adopted, utilizing a Saginaw steering box sourced from competitor General Motors. Performance models like the 71 Boss Mustang received a quick-ratio version of this box, offering a faster response and superior road feel compared to previous Ford systems.
The Heart of the Beast: The Boss 351 Engine
The soul of the 71 Boss Mustang was its unique engine. Unlike the track-focused Boss 302 or the homologation-special Boss 429, the Boss 351 was designed as a high-performance street engine derived from the 351 Cleveland (351C). The Boss 351 featured the 351C’s best attributes: large-port, canted-valve cylinder heads (4V versions), a high-nodularity cast iron crankshaft, forged connecting rods, forged pistons yielding an 11.7:1 compression ratio (later revised to 11.0:1), a solid-lifter camshaft, an aluminum dual-plane intake manifold, and a large Autolite 4300-D carburetor. It was rated at 330 horsepower (gross), though likely underrated, and offered significantly better low-end torque and drivability compared to the high-revving Boss 302 it effectively replaced.
Performance Reviews: A Tale of Two Mustangs
Contemporary road tests confirmed the 71 Boss Mustang‘s impressive straight-line speed, but often criticized the platform itself. Car and Driver, testing the 71 Boss Mustang, praised the engine’s performance, deeming it comparable to cars with 100 cubic inches more displacement. Their test car ran the quarter mile in 14.1 seconds at 100.6 mph, with power-shifting yielding an even quicker 13.9 seconds at 102 mph – significantly faster than the Boss 302.
Car and Driver magazine cover featuring a yellow 1971 Boss Mustang during a road test
Excerpt from Car and Driver review showing 71 Boss Mustang performance specifications and commentary
However, Car and Driver had serious reservations. While noting the improved steering feel from the Saginaw box, they found the “Competition Suspension” overly stiff, resulting in a “punishing ride” without the handling finesse to justify it, unlike the contemporary Camaro Z/28. Significant understeer plagued the car, a step back from the well-balanced handling of the Boss 302. Furthermore, the dramatic styling came at a cost: the long hood, low seating position, high beltline, and thick rear pillars created poor outward visibility and compromised ergonomics, making the car feel larger and less agile than its predecessors.
Opening page of Motor Trend's 1971 Mustang comparison featuring the Boss 351, Mach 1 429, and 302 models
Motor Trend conducted a unique comparison, pitting the 71 Boss Mustang against a Mach 1 with the 429 CJ (370 hp gross) and a base model with the 302-2V (210 hp gross – corrected from original text error). Their Boss 351 test car was even faster than Car and Driver’s, clocking a blistering 13.8-second quarter mile at 104 mph. This handily beat the more powerful but heavier (by approx. 350 lbs due to engine, automatic transmission, and options like A/C) 429 CJ Mach 1, which ran 14.61 seconds at 96.8 mph. The significant weight difference, much of it over the front axle in the 429 car, likely exacerbated the Mustang’s inherent understeer.
Motor Trend comparison chart showing performance data for the 71 Boss Mustang, 429 CJ, and 302 Mustang
Motor Trend was more diplomatic about handling, noting the improved lateral grip and minimal body roll but also mentioning the need to use power to overcome understeer. They also reported wheel hop issues across all three tested Mustangs. While acknowledging the base 302 offered adequate performance and was perhaps closest to the original Mustang concept, the review highlighted how the extreme styling compromised comfort, particularly for taller drivers.
Why is the 71 Boss Mustang Often Overlooked?
Despite its potent Boss 351 engine and impressive drag strip performance, the 71 Boss Mustang struggles for recognition primarily due to its association with the larger, heavier, and stylistically controversial 1971-1973 Mustang generation. Criticisms regarding its handling dynamics, punishing ride, poor visibility, and deviation from the original pony car ethos overshadowed its engine’s brilliance. It remains caught between the more nimble earlier Mustangs and the later, emissions-choked Mustang II era, often forgotten in favor of its Boss siblings (302 and 429) or the Shelby models.
The 71 Boss Mustang was undeniably one of the quickest Mustangs of the muscle car era, powered by an exceptional engine. Had Ford fitted the Boss 351 engine into the lighter, better-balanced 1970 chassis, its legacy might be vastly different, potentially ranking it among the most legendary Mustangs ever built.
Bright red 1971 Ford Mustang Boss 351 parked outdoors, showcasing its aggressive stance and styling
Nevertheless, the 71 Boss Mustang remains a fascinating and formidable machine. It perfectly encapsulates the excesses and compromises of the late muscle car era – incredibly fast in a straight line, aggressively styled, and powered by one of the great V8 engines, yet flawed in its execution as an overall package. For those who appreciate raw power and the unique character of early 70s muscle, the 71 Boss Mustang stands as a potent, if imperfect, testament to Ford’s performance heritage.
