In my series on the Ford 335-Series engines, I covered in detail the performance potential designed into Ford’s 351C. Unfortunately, this engine really had little opportunity to shine with minimizing engine emissions becoming far more important than all out performance shortly after the 351C’s introduction. In the North American market, Ford built one 351C variant that was nearly uninhibited – the Boss 351. This engine was a one year wonder, limited to Ford Mustang Boss 351. After 1971 the Mustang Boss 351 was dropped. Although the engine continued into 1972 as the 351 HO, it was substantially neutered to meet the tightening emissions and therefore lost the Boss moniker.
When people talk about legendary muscle cars, they talk of Hemi Mopars, Chevelle Super Sports, GTOs and Ford Mustangs. Getting specific about Mustangs, people will mention Shelby Mustangs, Boss 302s, 428 Cobra Jets and Boss 429s. Rarely, is the Boss 351 ever mentioned. Yet, despite the lack interest, the Boss 351 was one of the best performing Mustangs of the era. The Boss 351 punched above its weight class. It was significantly smaller in displacement than most other cars that had similar performance and was definitely one of the best performing “small-block” cars of the era. However, this excellent engine was only available in the larger and heavier 1971 Mustang. This is a Mustang that wasn’t totally accepted then or now by enthusiasts.
For 1971, the Ford Mustang was heavily reworked and restyled. The Mustang grew in length, width and weight, becoming the largest and heaviest Mustang up until that time. Despite these major revisions, it continued to use the old Falcon chassis that it had been based off since its inception. The new racy styling was one of Ford’s last cars to be styled without the soon to be imposed government regulations. And the stylists took it to the extreme, creating a car with all of the performance styling trends of the day.
While often people think of these as the big bloated Mustangs, realistically, the size growth wasn’t as substantial as the styling may have suggested. Over the 1970 model, the 1971 Mustang grew about 2” in length and about 2.5” in width. Yet even with this growth, the Mustang was on par with the Camaro in size and was actually smaller than the Challenger or the Javelin.
Ford enlarged the engine bay in the 1967 Mustang to fit the larger FE engines, but it still wasn’t large enough to house the new 385-series engines. This was resolved with the 1971 Mustang, which had a new larger engine bay, capable of housing the 429 engine that replaced the former 428 engine. When the front end was widened, Ford also updated the front suspension and steering. The track was widened, the front suspension geometry was altered, and Ford finally used an integral power steering system. Ford actually went to its competitor for steering, and used a Saginaw steering box. The Boss 351 and other performance Mustangs used a quick ratio box that was superior to the Ford built boxes, with a faster ratio and better road feel.
Despite the growth in size and width, the elements were still there to make a great pony car. It had trendy racy styling, a hot engine line-up, and improved suspension and steering. Yet, despite all this this Mustang largely missed the mark in the eyes of the press and many enthusiasts. Car and Driver tested a 1971 Boss Mustang, and were impressed with the performance of the 351C, but had many reservations about the Mustang itself. The drag strip performance was very good, deemed to be comparable to cars with 100 cubic inches more displacement. It ran with some of the quickest Mustangs of that era, with a 14.1 sec quarter mile at 100.6 mph. Car and Driver achieved an even better 13.9 secs at 102 mph with power shifting. It certainly was a substantial improvement over the Boss 302 it replaced and the extra displacement improved the low end response.
Car and Driver noted the improved steering and praised the Saginaw steering for its precise feel, but it had serious reservations about the suspension. Ford’s competition suspension consisted of very stiff springs which resulted in a “punishing ride.” However, unlike Chevrolet’s Camaro which had excellent dynamics, this Mustang did not have the dynamics to justify the overly stiff ride. Further, Mustang suffered from significant understeer. This certainly wasn’t an improvement over the Boss 302 predecessor, which had handling that Car and Driver praised for being well balanced. The 1971 Boss 351 had the ingredients for a decent suspension and it had the potential to be improved upon over the 1970 Boss, but ultimately the execution was poor. On the plus side, the large wide tires, stiff springs allowed for good lateral grip – just make sure you keep it on smooth roads.
Styling trends of the early 1970’s American muscle cars were taken to the extreme, and the 1971 Mustang falls into this category. Many, including me, like this extreme uninhibited styling, but it does come with compromise. The ’71 Mustang was definitely a stylist car and much of the other elements of the car were compromised to achieve the stylist vision. Car and Driver admitted the Mustang had attractive and attention getting styling, but much like a modern Camaro, the visibility of the Mustang was compromised for this styling. The long hood, low slung interior with high sills and large rear pillars made for terrible outward visibility and poor interior ergonomics. The styling not only made the car look larger than it was, it also made the car feel like it was much larger than it was when piloting it from the driver’s seat. The Mustang certainly no longer had the small agile feel of the original Mustang.
Undoubtedly, Car and Driver was impressed by the performance of the Boss 351 engine, but it was quite apparent the car did not live up their expectation of what they thought a proper GT car should be. In comparison, the Chevrolet Camaro of this time was generally better received, despite its same large size and lack of space efficiency. The 1971 Camaro was hindered by a lower compression LT-1, which didn’t perform as well as the Boss 351. However, the Camaro’s racy styling didn’t compromise visibility and it had some of the best handling dynamics of any American made car of that era. Even with less straight line performance than the Boss 351, the Camaro was simply a better executed performance car.
The Boss 351 was tested by numerous publications in 1971, but Motor Trend took had a unique comparison. It tested the Boss 351 along with two other variations of the Mustang. One was a Mach 1 equipped with a 429 CJ engine, making 370 hp (gross), while the other was equipped with the base 302-2V, making 200 hp (gross). Although the Mustang had changed considerably since its introduction, it still could be equipped for a wide variety of customer tastes, which was part of the original concept. This concept was very well executed in 1965, by 1971 things had gone off track somewhat.
As much as the high-performance and sporty image had helped sell Mustangs, the majority of the Mustangs sold were not high performance machines. The styling of the 1971 Mustang was raciest yet, and it sure looked like it was going 100 mph standing still. Nonetheless, this extreme styling compromised the Mustang when it was used for more ordinary transportation. One of these compromises noted by Motor Trend was that the low slung styling limited comfort for people over 5’10” tall.
Like Car and Driver, Motor Trend was impressed by the Boss Mustangs straight line performance. Interestingly, Car and Driver claimed its test car was probably the fastest Boss 351 you could get due to its expert tuning, but it actually had one of the slowest recorded times of the 1971 Boss 351 road tests. Motor Trend was able to beat the C/D time with, ripping through the quarter mile at 13.8 seconds and 104 mph. It handily beat the more powerful, but heavier and taller geared 429 CJ, which ran 14.61 secs at 96.8 mph. It was notable that the 429 Mustang was considerably heavier, about 350 lbs, which was attributed to the heavier engine, the automatic transmission, and the additional options, such as air conditioning. The weight distribution isn’t listed, but the 429 car would be significantly heavier on the nose, which certainly wouldn’t have helped with Mustang’s understeer.
Motor Trend was more tactful when addressing Mustangs handling, focusing on the improved lateral grip from the wider track, and the minimal body roll from the sway bars. Of course they do mention that power could be used to induce oversteer – a technique that would be helpful as the Mustangs inevitably starts plowing through the corners. Motor Trend complained of wheel hop problems with all three Mustangs.
The 302 Mustang is noted to have adequate acceleration and handling. Motor Trend says it doesn’t handle as badly as they expected, but their description of trying to violently induce oversteer to overcome understeer in corners doesn’t suggest it would be a corner carver by any stretch. Motor Trend claims that the 302 Mustang is the best buy of the group and was closest to the original Mustang concept. I would agree that this car was the closest to the original concept, but I have to question what, if anything about this particular ’71 Mustang is improved upon compared to a 1965 Mustang 289-2V?
The 1971 Mustang Boss 351 was an impressive performance car. It was one of the best performing Mustangs of the era, even if it wasn’t the most balanced or best handling. Had the Boss 351 been used in the lighter and better balanced 1970 Boss 302, it may have been remember as one of the most legendary Mustangs.
Nevertheless, despite all of its flaws, I like the Boss 351 Mustang. It looked great in my eyes, was fast and had one of the coolest muscle car engines of all time. It’s far from perfect, but what muscle car was?