Ford Mustang Boss 429
The mythical Mustang Boss 429 is a proper muscle car legend. Conceived in 1969 as a pure racing engine intended for use in the NASCAR championship, the Boss 429 featured a different engine architecture than the rest of Ford’s big blocks. First, the Boss 429 was much broader and had semi-Hemi combustion chambers, which ultimately produced more power and torque (via Mustang Specs).
Rated at 375 hp by the factory, in reality, this unit produced over 500 hp and much more in race trim. Ford decided to put this engine into the Mustang, creating a limited-production Boss 429. Still, NASCAR chose not to homologate it since the series only accepted intermediate and full-size cars, and the Mustang was a pony car model.