The 1969 Ford Mustang BOSS 520 Was The Ultimate Mustang

The forgotten Mustang BOSS 520 was a track weapon from the 1960s that never went racing

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The legacy of the Ford Mustang dates back to 1962 with the Ford Mustang I concept car. Since then, we have gotten many iconic interpretations of the car, including high-performance variants like the Shelby GT350, GT500, BOSS 302, and the BOSS 429, which is considered to be the ultimate ’Stang. The BOSS 429, itself, was the basis for other interesting projects such as the mid-engine Ford Mustang LID, but there was another, more conventional version that, sort of, made it - the Mustang BOSS 520.

Built to compete

The 1969 Ford Mustang BOSS 520 Was The Ultimate Mustang
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In 1969, Ford was doing quite well in NASCAR but was getting annihilated at Trans-Am racing. Former GM executive, Simon "Bunkie" Knudsen who moved to Ford in February 1968, commissioned a Ford Mustang that would utilize the brand’s NASCAR technology for SCCA racing. However, clashes with other Ford executives, mainly Lee Iaccoca, led to Knudsen getting fired from Ford in September 1969. The project ended up being executed by Ford subsidiary, Kar Kraft Engineering, which is also responsible for the Mustang BOSS 429.

The two original BOSS 520 prototypes still exist

The 1969 Ford Mustang BOSS 520 Was The Ultimate Mustang
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Kar Kraft Engineering managed to complete two prototypes, which were officially designated as "Composite Mustangs" and unofficially, "Quarter Mustangs". The latest reports indicate that both prototypes still exist. Moreover, about 40 years later, someone did a faithful, money-no-object replica of the BOSS 520.

Performance & Drivetrain

The 1969 Ford Mustang BOSS 520 Was The Ultimate Mustang
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The basis for this ultimate 1960s Mustang was, of course, the BOSS 429, with which the BOSS 520 shared a chassis. However, the engine was a 520 cubic-inch (8.5-liter) V-8. While there are no exact output figures quoted, we know that the single replica that exists makes 770 horsepower and 720 pound-feet (976 Nm) from the same 520 cubic-inch, carburated, Kasse-tuned BOSS Nine engine, found in the original prototypes. The BOSS 520 replica, reportedly, features a few aftermarket goodies and a custom tune by Jon Kaase, himself.

The V-8’s massive power goes to the rear axle through a Tremec T56, six-speed manual, and a Currie nine-inch rear end with 3.89 rear gears, Detroit Locker, posi differential, and 35-spline axles. Stopping power is entrusted to Baer power brakes with six-piston calipers and 14-inch drilled and slotted rotors. The slightly stretched wheel arches accommodate BF Goodrich G-Force T/A tires with 245/40ZR18 size at the front and 335/30ZR18 at the rear, and there are RideTech coil-overs installed.


The 1969 Ford Mustang BOSS 520 Was The Ultimate Mustang
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We only have the replica images to go by, but we know that the BOSS 520 featured a 1969 Mustang Fastback body with a 1969 Shelby GT500 nose and rear panel - something the replica has recreated to the letter, which makes it a good reference point. A lot of custom work was needed to faithfully replicate the aesthetics of the BOSS 520, which included Dynacorn metal and fiberglass as well as a bespoke front hood and valence, and side air scoops. The replica features a few modern touches such as the LED headlights and wheels, but other than that, it is as faithful to the originals as it can be.


The 1969 Ford Mustang BOSS 520 Was The Ultimate Mustang
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The interior is heavily customized and the most notable feature, just like on the original BOSS 520s, is the Mercury Cougar dashboard, which has been heavily customized here to accommodate vintage A/C, modern infotainment system, and other modernities, neatly integrated into the car’s interior.

There’s leather throughout the whole interior except in the back where the rear seat has been deleted and instead a custom panel has been fabricated in order to house the two Kicker subwoofers, Kicker QS speakers, and a Kicker IX amplifier. Being a powerful muscle ca, there’s plenty of

Can a replica be better than the original?

The 1969 Ford Mustang BOSS 520 Was The Ultimate Mustang
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While it’s not easy to answer this question, the BOSS 520 replica is a truly high-end build where no expense was spared, in order to reimagine a long-forgotten classic Muscle car. While the original Ford Mustang BOSS 520 prototypes never went into production, they are still out there, most probably, secluded in a prototype warehouse with cars like the Ford Roush GN34 and the mid-engine BOSS 429 we mentioned earlier. As for the BOSS 520 replica,it last changed hands about 10 years ago, for the price of $119,900, according to the Classic Cars listing.

Source: RK Motors

Dim Angelov
Dim Angelov
Born in 1992, I come from a family of motoring enthusiasts. My passion for cars was awoken at the age of six, when I saw a Lamborghini Diablo SV in a magazine. After high school I earned a master’s degree in marketing and a Master of Arts in Media and Communications. Over the years, I’ve practiced and become skilled in precision driving and to date have test driven more than 250 cars across the globe. Over the years, I’ve picked up basic mechanical knowledge and have even taken part in the restoration of a 1964 Jaguar E-Type and an Alfa Romeo Giulia Sprint. Lately, I’ve taken a fancy to automotive photography, and while modern cars are my primary passion, I also have a love for Asian Martial Arts, swimming, war history, craft beer, historical weapons, and car restoration. In time, I plan my own classic car restoration and hope to earn my racing certificate, after which I expect to establish my own racing team.  Read full bio
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