If you pop the hood on your car and yank out the plastic cover beneath it, you'll see a beautiful bit of mind-boggling engineering: the internal combustion engine. Today's engines harness around 100 explosions of fuel and oxygen each second, generating massive power with minimal emissions.

That's great, but tightening pollution standards around the world mean automobiles must become increasingly efficient. Electric cars offer one way forward, but they remain expensive and hobbled by range anxiety—the fear, often unfounded, that you'll end up stranded with a dead battery. Internal combustion isn't going anywhere anytime soon, with advancements like turbochargers, direct injection, and variable valve timing squeezing more miles from every gallon.

Achates Power in San Diego believes it has a better way: Ditch the design that has dominated engine design for the past 130 years in favor of an idea abandoned in the 1940s and see a 30 percent bump in efficiency.

Most automotive engines, from the single-cylinder, one-horsepower unit Carl Benz created in 1885 to the 16-cylinder, 1,500-horsepower beast in the Bugatti Chiron, use a four-stroke reciprocating design. It's a relatively simple idea: A piston in a cylinder draws in air and adds fuel during the intake stroke. The compression stroke squishes that mixture and introduces a spark, creating an explosion that drives the piston down, generating power during the power stroke. The cylinder then rises during the exhaust stroke, expelling spent gasses. The cycle repeats, thousands of times each minute.

Achates wants to chuck that out the window in favor of the opposed piston engine. This setup uses two pistons in each cylinder. The ignition of fuel and air creates an explosion that drives the pistons apart, generating power. Such engines are simpler, because they don't use valves or camshafts. They saw some use in locomotives and military vehicles until engineers abandoned them in the 1940s because of the difficulty of making them run cleanly and efficiently. Achates thinks it has cracked that problem. We paid a visit to find out how—check out the video above to see what we learned.