Napier Deltic 18-Cylinder 88-Liter Opposed Two-Stroke Triangle EngineThe Napier is a complicated extrapolation of a basic opposed-piston engine. Your average “engine” has cylinders and pistons lined up with a cylinder head on top feeding the gas and air mixture. An opposed-piston engine replaces the cylinder head with another set of pistons, each sharing a common cylinder, like a boxer engine but with no heads.The engine you see here has three opposed-piston engines in a chain, forming a triangle. This setup made 3,700 hp when turbocharged. A much simpler bank of six cylinders (12 pistons) could power 18-wheeler trucks very efficiently. A company called Achetes Power is developing opposed piston engines in San Diego, Calif.