Although rated at 375 hp, it is rumored that they escaped the factory with close to 500 hp.The Mustang Boss 429 is the dream of most Mustang enthusiasts and it was made to meet NASCAR regulations. Fewer than 1,400 were built making the Boss 429 Mustang a rare horse indeed.
The Boss 429 engine was derived from the Ford 385 engine. It used four-bolt mains, a forged steel crank and forged steel connecting rods. The engine featured aluminum cylinder heads, with a modified Hemi type combustion chamber which Ford called “crescent”.
This car was basically hand-built. Because the engine wouldn’t fit in a standard Mustang without extensive modifications, Ford farmed out its assembly to Michigan-based Kar Kraft. In appearance, very little distinguished the Boss 429 other than a hood scoop and trunk-mounted spoiler.The Boss 429 (also known as the “Boss 9″ by enthusiasts) is arguably one of the rarest and most valued muscle cars to date. In total there were 1358 original Boss 429s made. The origin of the Boss 429 came about as a result of NASCAR. Ford was seeking to develop a Hemi engine that could compete with the famed 426 Hemi from Chrysler in NASCAR’s Sprint Cup Series (then known as “Grand National Division”). NASCAR rules required that at least 500 cars be fitted with this motor and sold to the general public. After much consideration, it was decided by Ford that the Mustang would be the car that would house this new engine.
The Boss 429 engine was derived from the Ford 385 engine. It used four-bolt mains, a forged steel crank and forged steel connecting rods. The engine featured aluminum cylinder heads, with 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 style seal to seal it tight. The Boss 429 engine used a single Holley four barrel carburetor rated at 735 CFM mounted on an aluminum intake manifold that flowed well for its time. 1969 cars featured a hydraulic lifter camshaft while 1970 models got a mechanical lifter camshaft along with an improved dual exhaust system though rated power output stayed the same.
You could call this a run-away Mustang as it sure ain’t a pony!