1969–1970 Mustang Boss 429: The Epic Road-Legal Pony Car With a NASCAR Engine

1969 Ford Mustang Boss 429 11 photos
Photo: Ford Motor Co.
1969 Ford Mustang Boss 4291969 Ford Mustang Boss 4291969 Ford Mustang Boss 4291970 Ford Mustang Boss 4291970 Ford Mustang Boss 4291969 Ford Mustang Boss 429 Interior1970 Ford Mustang Boss 429 Interior1970 Ford Mustang Boss 429 Interior1969-1970 Boss 429 EngineFOrd Mustang Boss 429 Assembly Line
To homologate a new engine destined for NASCAR use, Ford decided to squeeze it into a road-legal Mustang, creating the Boss 429, one of the most iconic pony cars ever built.
In the 1960s, the Blue Oval was hellbent on dominating motorsport and competed on many fronts. This ambition resulted in the birth of several legendary cars, including the Boss 302 and Boss 429 Mustangs, which were both built to meet homologation requirements for two distinct racing classes.

The former was built to topple the Z28 Camaro in the Sports Car Club of America (SCCA) Trans-Am championship, while its more powerful sibling was born to homologate the new 429 cu in (7.0-liter) V8 for NASCAR.

The powerplant in question was a humongous big-block unit rated at 375 hp and 450 lb-ft (610 Nm) of torque, although many speculate it could produce more. It was fitted with a forged steel crankshaft and conrods made from the same material, four-bolt main caps, and aluminum heads that stood atop combustion chambers with an innovative semi-hemispherical design. Additionally, it used free-flowing header-style exhaust manifolds, while a lightweight aluminum high-riser intake housed a big 4-barrel Holley carb.

1969\-1970 Boss 429 Engine
Photo: Ford Motor Co
The 1969 cars featured a hydraulic lifter camshaft, while those built for the 1970 model year got a solid lifter version along with an improved dual exhaust system.

Although the Mustang was extensively redesigned to accommodate big blocks in 1967 and another major revamp had just been completed, the engine bay was still not wide enough for the colossal 429.

To solve the problem, Ford contracted Kar-Kraft, an independent company located in Dearborn, Michigan, that worked closely with the carmaker on numerous projects, including the GT40 race program.

FOrd Mustang Boss 429 Assembly Line
Photo: Ford Motor Co
The carmaker shipped 4-speed Cobra Jet SportRoofs Mustangs to the Dearborn facility, where Kar-Kraft engineers stripped them down and modified them extensively. The shock towers were moved slightly forward, the A-arms were lowered, and heavy-duty shocks were mounted, along with stiffer sway bars, a locking differential, and high-performance front disc brakes.

The Boss 429 was essentially built as a test mule for the race-bound engine, but its appearance was by no means neglected. Larry Shinoda, the ex-GM employee who designed the C2 Corvette, was in charge of making both Boss variants stand out from other Mustangs, and as we can see, he undoubtedly succeeded.

Unlike the 302, this high-performance model didn’t feature a custom decal package, but the massive scoop mounted on the hood made it instantly recognizable. Installed to feed the hungry engine with plenty of air, it was (and still is) the largest ever fitted on a mass-produced Mustang. For the 1970 model year, one of the few aesthetic changes saw the scoop painted flat black.

1969 Ford Mustang Boss 429
Photo: Ford Motor Co
Other exterior upgrades included widened rear fenders with integrated air ducts (removed in 1970) and a chin spoiler shared with the 302, meant to reduce drag at high speeds. Also borrowed from its sibling was the rear spoiler that, in this case, was optional.

Inside, the story was different. Unlike the Shelbys of the era, the 429 came standard with the Interior Decor Group, which included vinyl bucket seats and wood-grained trims. The first-year models were only available with black interiors, with a predominantly white option added a year later.

Among the notable features that set it apart from lesser Mustangs were a set of knobs for a manual choke and ram-air actuation, as well as deluxe seat belts. The optional air conditioning offered on all other models was unavailable due to the sheer size of the engine.

1970 Ford Mustang Boss 429 Interior
Photo: Ford Motor Co
The Boss 429 is extremely sought-after nowadays, but customers weren’t so eager to buy one during the two years that it was available. Fans were hoping that this would be the best pony car ever built from every point of view, while Ford just wanted to homologate the powerplant and didn’t put too much work into anything else. It was priced in the same region as the GT500, which was better equipped and wasn’t far off in terms of performance, so only 1,357 units were sold.

Both the 429 and 302 Boss models were discontinued for 1971, along with the iconic Shelbys. A 351 Boss was sold that year, but it was also dropped due to poor sales, ending the high-performance era of the first generation.

Fitted with one of the largest big-block engines ever utilized by Ford in a production vehicle, the legacy of this iconic Mustang lives on even if it was never a commercial success.
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About the author: Vlad Radu
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Vlad's first car was custom coach built: an exotic he made out of wood, cardboard and a borrowed steering wheel at the age of five. Combining his previous experience in writing and car dealership years, his articles focus in depth on special cars of past and present times.
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