Cummins says its four-cylinder QSB3.3 and QSB4.5 diesel engines (75- to 160-horsepower) will meet EPA Tier 4 Interim emissions restrictions in 2012 with fuel efficiency improvements up to 5 percent. Proven 3.3- and 4.5-liter blocks and high pressure common rail fuel systems remain essentially the same. Emissions are reduced with cooled exhaust gas recirculation (EGR) for NOx control and exhaust aftertreatment for removing particulate matter (scaled-down versions of technology previously announced for the six-cylinderQSB6.7). An upgraded turbocharger with electronic control will manage EGR flow at all engine speeds. "Our four-cylinder development program for Tier 4 Interim was driven by the need to avoid the complexity of increasing displacement or overloading the engines with complications such as dual turbochargers,” says Hugh Foden, executive director, Cummins off-highway business.