The Ford Mustang Boss 429 was a high performance version of the Ford Mustang offered by the company in both 1969 and 1970. The Boss 429 is considered to be one of the rarest and most valued muscle cars in history. The rarity of the vehicle comes as a result of the low number built, a total which only comes to 859. The Boss 429 engine was constructed from the Ford 385 engine. However, the Mustang’s body was not wide enough to hold the larger Boss 429 engine, consequently, Ford hired Kar Kraft to alter existing 428 Cobra Jet Mach 1 Mustangs to adequately fit the new Boss 429 engine.
Production on the Boss 429 began in 1968 in Brighton, Michigan. Kar Kraft made notable changes to the Mustang, including the widening of shock towers as well as extending out the inner fenders to make room for the engine. The mounts for the front suspension were chopped and displaced to create space for the block and exhaust manifolds. Additionally, the battery was moved to the trunk and a stiff sway bar was added to rear end. Also, a hole was cut in the hood and a manual controlled hood scoop was added to these cars. These cars were rated conservatively at 375 hp (280 kW) and 450 lb·ft (610 N·m) of torque. In reality, actual output was well over 500 horsepower (370 kW). Due to rising insurance costs and legal issues the dealers and manufacturers only listed 375 hp (280 kW).
Coompared to other Mustangs of the era both the 1969 and 1970 model displayed a toned down exterior. Generally, the car featured an especially clean look that was not typical of most Mustangs that Ford had built. Unfortunately sales started to drop off for the 1970 Boss 429 Mustangs and with rising production costs, internal Ford problems, and gas costs it was decided that 1970 would be the last year of the Boss 429. Currently, these cars are highly desirable. In recent years, auctions at Barrett-Jackson and on Ebay have brought bids of over $350,000.