Navistar has unveiled several upgrades to its International A26 engine, contributing to a 10% overall boost in fuel economy since the engine was first launched.

The latest enhancements – representing a 4% improvement – come from combustion enhancements, optimized engine temperatures, air management, and a higher horsepower output.

The compression ration rises from 18.5:1 to 20.5:1, and combines with maximized fuel injection pressures. Cylinder head coolant passages have been designed to reduce parasitic losses at the water pump, and combines with a variable water pump that optimizes run time.

Meanwhile, an optimized exhaust gas recirculation cooler and intake throttle vale improve charge air flow, Navistar says. A variable geometry turbocharger also delivers desired boost pressure across a wide range of engine speeds and loads.

The higher horsepower output makes it possible to operate at a lower rpm.

The 13-liter A26 is based on MAN’s D26 engine crankcase, and deliver up to 515 hp and 1,850 lb-ft of torque.

Previous updates such as optimized engine and transmission calibrations mated with an Eaton Endurant transmissions, a direct-drive 2.15 ratio, and aerodynamic wheel coverings accounted for a 6% improvement in fuel economy since the engine was first released.