The Hefley engine was a different style of engine. It could actually change the displacement depending on the demand required. It could in theory power everything from a Motorcycle to a Semi with the right combination. And it could provide full power at any of the displacements, which allowed it to sip the fuel when running at small displacement, and yet could give huge amounts of power and torque when needing a large engine.
The newer design of the Hefley engine was even able to run on different alternative fuels. This has been around for a century though. The first diesel engine ran on peanut oil. The Grand Canyon Railroad Steam Locomotive runs on recycled vegetable oil. Chrysler in the 60′s had a turbine powered vehicle that would run on everything from Whiskey to rubbing alcohol if needed. The ability to use so many different styles of fuel is definitely a worth while endeavor in the modern age.