All the hand wringing over recirculating exhaust gas through a truck engine's intake to meet October 1 emissions limits may have obscured the advantages of the variable-geometry turbochargers necessary to make EGR work. Cummins claims the Holset variable-geometry turbochargers on this year's ISX, ISM, and ISB (15 liters, 10.8 liters and 5.9 liters) are the EGR engines' most important features. The electronic controller adjusts vane positions in the turbine to make it push the optimum amount of air into the cylinders for complete combustion at all engine speeds. The result is significantly improved throttle response. The ISX, with dual overhead camshafts, is a weight-saving replacement for the venerable N14.
