In 1956, General Motors made a groundbreaking achievement in automotive engineering with the introduction of the XP-500, the world's first free-piston automobile. Developed by the General Motors Research Laboratories over a span of 14 months, the XP-500 made its public debut shortly before the dedication ceremony of the GM Technical Center.
Resembling the gas-turbine-powered Firebird II, the XP-500 featured a sleek design with a rounded all-glass roof and a low, horizontal grille opening. Its hood sloped down from the windshield, concealing the flat Hyprex engine housed in the engine compartment. The vehicle's rear fenders had an elegant wing-like shape that arched over the wheels toward the tail.
Powering the XP-500 was the GM 4-4 Hyprex engine, a revolutionary piece of engineering. This engine consisted of two parallel cylinders, each equipped with horizontally opposed pistons. The air-fuel charge ignited between the pistons, generating compressed air that was channeled into a turbine, providing additional power to the drivetrain. With an impressive output of 250 horsepower, the XP-500 showcased the potential of this innovative engine design.
However, despite its remarkable achievements, the free-piston automobile faced technical limitations and alternative propulsion methods showed more promise in subsequent research. Consequently, General Motors discontinued further development of the free-piston automobile just three years after the completion of the XP-500.
The XP-500 stands as a testament to General Motors' commitment to pushing the boundaries of automotive innovation. While it may not have continued its journey beyond the experimental stage, this pioneering vehicle has left a lasting impact on the automotive industry, inspiring further advancements and shaping the course of future development.
Images: Custom_Cab's photostream; General Motors Archive