How Much HP did the ’69 Boss 429 Mustang make?

Some say that the Boss 429 mustang is one of the Greatest Muscle cars of All Time. It was originally designed for NASCAR at a time when the Chrysler 426 Hemi was the car to beat. The car was rumored to be capable of speeds near 175mph even in street trim.

Many of these cars still have the original Magnum 500 wheels and the flat black front chin spoiler is unique. Other than the sculptured fenders, wider tires and the Boss 429 logo, the Boss 429 looked very similar to the other mustangs of the same year. The large air scoop on the hood was also a bit of a give-away about the beast of an engine.

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Although the factory rated the Boss 429 SOHC engine at 375Hp, it was really closer to 600HP. It was a thin-wall block with a 4.36-inch bore and 3.59-inch stroke which was based on the 429/460 engine design. The most unique feature was the massive Semi-Hemi cylinder heads developed to go up against the canted valve Chevy motors and the Hemi head Mopar engines on the speedways at the time.

The NASCAR prepared engines came out of the Holman-Moody race shops in Charlotte, North Carolina. They were Ford’s unofficial technology center for stock car racing back then. In 1969 and 1970 which were the only years when the Boss 429 was legal in competition, Holman-Moody’s driver was the famous David Pearson. Porting heads in the shop was Robert Yates.

Ford was so secretive about the development of this engine, it had an almost cult-like following. Because of being designed to compete on the track, the 7 liter semi-hemi engine was able to be run at 9000rpm for extended periods of time.

Since NASCAR rules required 500 production cars to be built with the Boss 429 engine, Ford produced 857 Boss Mustangs in 1969 from the KK-Brighton plant in Brighton, Michigan. 2 of the Boss 429 engines were reported to be installed in ’69 Mercury Cougars. 500 more Mustangs were produced in 1970. The cars were actually sent from the assembly plant to be hand built at the Kar-Kraft shops in Michigan.

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Ford Designer Larry Shinoda was in charge of the Boss 429 Mustang project and it is said that he came up with the Boss name as a tribute to Bunkie Knudsen who was President at Ford during this time because he always just called him “Boss”.

Read more at gearheads.org

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