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Its Woody Time HOT! Mustang Content Archive

1969-70 BOSS 429 MUSTANG




859 (Includes 2 Boss 429 Cougars)




The Boss 429 is one of the most unique Mustangs made. Its uniqueness lies in its rarity, its engine and simply for the fact that so much effort went into modifying the basic Mustang to make the Boss 429 engine fit.

Visually, the Boss 429 sits lower than other 1969-70 SportsRoof Mustangs. And compared to the Mach 1 or Boss 302, it has an understated image. Save for the Boss 429 fender decals and large hood scoop, the Boss 429 doesn't have any stripes, blacked-out trim, wheel or rocker panel moldings or even chrome dual exhaust tip outlets.

The Boss 429 Mustang was a limited production Mustang designed to homologate the Boss 429 engine for NASCAR racing. It would have been more logical to use the Torino, after all that was the body style used for NASCAR, but for image reasons, Ford decided on the Mustang instead.

All were built at the Kar Kraft facility in Brighton, Michigan. This was the same facility that Ford used to build the Le Mans Ford GTs. Partially completed SportsRoof Mustangs that were destined originally receive the 428SCJ engine, were modified at Kar Kraft to accept the large 429 engine. The main difficulty was getting the Boss 429 engine to fit the Mustang's engine compartment. To do so, the shock towers were relocated outward (by hand) and while they were at it, the suspension was lowered and moved further outwards 1 inch, using spindles and control arms unique to the Boss 429. This made the Boss 429 handle much better than other big-block equipped Mustangs. Other features included Boss 429 fender decals, manually controlled hood scoop, a front spoiler that was shallower than the Boss 302 spoiler, color keyed dual racing mirrors, engine oil cooler, trunk mounted battery, close-ratio four speed manual transmission 3.91 rear axle with Traction-Lok, 3/4 inch rear sway bar (the first Mustang ever to have a rear bar), chrome 15x7 Magnum 500 wheels with F60x15 Goodyear RWL Polyglas GT tires. All Boss 429s came with the Deluxe Decor interior, 8000 rpm tachometer and AM radio.

The Boss 429 engine was based on a strengthened version of the production 429. These blocks have HP429 cast into the front of the block (driver's side). It used four bolt mains, a forged steel crank and forged steel connecting rods. The big deal with this engine are its aluminum cylinder heads which featured a modified Hemi type combustion chamber which Ford called "crescent". These heads used the "dry-deck" method, meaning no head gaskets were used. Each cylinder, oil passage and water passage had an individual "O" ring to seal it. The Boss 429 used a single Holley four-barrel carburetor rated at 735 CFM mounted on an aluminum intake manifold. 1969 versions used a hydraulic lifter camshaft; 1970 models got a mechanical lifter camshaft along with an improved dual exhaust system.

Each Boss 429 Mustang came with a KK sticker placed on the inside of the driver's door above the Ford Warranty Plate which signified Kar Kraft's production number. The first Boss 429 was numbered "KK NASCAR 1201" while the last 1969 is numbered 2059. Some Boss 429s may have this silver tape stripe missing; a small brass plate was substituted by Kar Kraft on a small number of cars.

Besides the Boss 302, the Boss 429 was the only other Mustang that had its Serial number stamped on the back side of the engine block assembly, on the inner front fender panels, on the transmission housing and on the chassis itself.

1969 Boss 429 Mustangs were available in five colors: Wimbledon White, Royal Maroon, Raven Black, Black Jade, and Candy Apple Red. 1970 versions were painted Grabber Blue, Grabber Green, Grabber Orange, Calypso Coral and Pastel Blue. All 1970 Boss 429s came with a gloss black painted hood scoop.

One would think that the Boss 429 would have been a street terror- given its impressive specifications. At best, in stock form, it equaled the 428CJs performance. The usual after market bolt-on modifications were extremely effective on waking the engine up. But as far as Ford was concerned, there was no reason to promote this Mustang- it's only purpose for being was to get that monster engine homolugated.




1969 Boss 429 Mustang



375hp Boss 429 V-8


Four-speed manual

Axle Ratio:






0-30 mph


0-60 mph


0-100 mph


Standing 1/4 mi

14.09 @ 102.85 mph

Top speed

118 mph


Car Life 7/69