Increasing Power and Efficiency

Over the years, 2 stroke engine manufacturers competed not only to build the most powerful engines, but also the most efficient ones. Efficiency becomes even more crucial when discussing engines in the 115 to 150 hp range. These outboards are best suited for boat owners who don’t mess around – they want to get from point A to point B quickly, and reliability is key. Still, it would be a shame to waste a perfectly good fuel/oil mixture.

Loop charging, also known as Schneurle porting, is a method by which transfer ports force the fresh fuel/air mixture into the combustion chamber as soon as it enters the cylinder. This discourages fuel from being lost through the exhaust port, improving efficiency as well as engine power. The method got its moniker from Anton Schneurle, a German scientist who invented a form of it in the 1920s.

Prior to the widespread of loop charging, 2 stroke engines trailed behind their 4 stroke counterparts in terms of power and efficiency. Today, Yamaha and other purveyors of 2 cycle oil feature a line of high-end, loop-charged engines that run the gamut from 115 hp to 150 hp. Without these innovations, boat owners wouldn’t be able to enjoy the speed and efficiency of modern outboard engines.