Using a 3 liter, 4 valves per cylinder, V6 Diesel engine model, this study investigates late intake valve closing (LIVC) time in an effort to reduce the fuel consumption of the engine. Two different intake cam duration technologies for diesel engines are evaluated using a 1-D engine simulation software code. The first method utilized for duration control delays the effective closing of the intake valve by moving one intake cam lobe with respect to the other baseline intake cam lobe. In the second method, the closing of both intake valves is delayed by the introduction of an adjustable dwell period during the closing portion of the valve motion. During this mid-lift dwell period, the lift is held at a constant value until it goes into the closing phase.The systems are evaluated and compared at 4 operating points of varying engine speed and load. At each operating point, while engine load is held constant, intake valve closing time is varied. The engine investigated uses a variable turbine geometry (VTG) turbocharger and at each operating point, two operating modes of the VTG are investigated; one with a constant boost pressure and the other with a constant vane position. Besides reporting the fuel consumption benefits of these devices, a full thermodynamic analysis is provided which explains why the devices perform in the manner claimed.