As in other flat engines (sometimes called boxer engines for the way their pistons resemble two fighters trading jabs), OPOC's pistons move horizontally. Hofbauer's aha! moment came one day when the former Volkswagen engineer was pondering the shortcomings of VW's boxer engine. "I thought, my God, if you just replace the cylinder head with a moving piston and cylinder ports, it might be less complicated."

It is—by a long shot. The engine requires less than half the parts of a similar four-stroke engine and is 30 percent lighter. The net result, says Hofbauer, is a 15 to 50 percent increase in energy efficiency, depending on the configuration. And thanks to its unique architecture and several key innovations, the OPOC releases far fewer emissions than a typical two-stroke. With a 240-hp diesel prototype, EcoMotors is focused now on the truck market; last February the company signed a licensing agreement with Navistar. "When the economy has recovered, the world will add 85 million combustion engines for cars and light trucks," Hofbauer says. "If we can offer an engine that is efficient and competitive in production costs, it will be a success."