"We’ve been covering Achates Power’s highly unusual inline-three-cylinder two-stroke engine with six pistons and two crankshafts for some time now, and it’s finally installed in a Ford F-150 truck for demonstration and fine tuning. The stats are pretty impressive if they prove reliable in production trim: 270 hp, 480 lb-ft, and 37 mpg combined fuel economy. The test engine is running 18.5:1 compression with direct gasoline injection. The long stroke of this 2.7-liter engine allows the pistons to extract maximum work, and because there are no cylinder heads (intake and exhaust flows through ports in the cylinder walls that get exposed at the extremes of the piston travel), there’s far less heat rejection to the cooling system. Achates says this helps deliver thermal efficiency of near 50 percent—and that’s before any in-vehicle thermal-management optimization work."