Engineers at Mahle (www.mahle-powertrain.com) recently completed a case study focused on reducing engine friction—using an existing 2-liter turbo GDI engine—resulting in a 2.2-mpg improvement in fuel economy. Their formula: The team reduced the main bearing size by 2.3 mm and redesigned the connecting rod and crankshaft to accommodate smaller journal sizes as a result of the bearing diameter changes. A revised assembled roller bearing camshaft design—the bearings are fitted directly onto the camshaft without an inner ring—replaced the plain bearing configuration and a 5-micron thick diamond-like coating was added, resulting in a 30% reduction in camshaft friction. The existing valves were replaced with hollow stem valves with two-piece welded heads—weighing 40% less while requiring 50% less spring force—resulting in further friction reduction during low-speed operation. “There is good potential for friction improvement on highly developed engines, but to achieve optimal results it’s important to look at optimizing the entire system,” says Neil Fraser senior principal R&D engineer at Mahle Powertrain.