15 Muscle Cars That Were Born to Break the Rules—And Did

9. 1969 Ford Mustang Boss 429

The 1969 Ford Mustang Boss 429 was built with one purpose: to dominate NASCAR.
Its massive, hand-built 429-cubic-inch V8 engine was designed for the racetrack, but Ford put it in a Mustang and unleashed it on the street, making the Boss 429 an instant outlier.
With its bulging hood and race-bred engineering, the Boss 429 broke the rules of factory muscle, offering an overbuilt powerhouse that remains legendary for its rarity and performance. Car and Driver