Very large scale, 3D, viscous, turbulent flow simulations, involving 840,000 finite volume cells and the complete form of the time-averaged Navier-Stokes equations, were conducted to study the mechanisms responsible for total pressure losses in the entire intake system (inlet duct, plenum, ports, valves, and cylinder) of a straight-six diesel engine. A unique feature of this paper is the inclusion of physical mechanisms responsible for cylinder-to-cylinder variation of flows between different cylinders, namely, the end-cylinder (#1) and the middle cylinder (#3) that is in-line with the inlet duct. Present results are compared with cylinder #2 simulations documented in a recent paper by the Clemson group, Taylor, et al. (1997). A validated comprehensive computational methodology was used to generate grid independent and fully convergent results. The methodology is comprised of four major steps forming an effective hierarchy: (1) proper computational modeling of essential flow physics; (2) exact geometry and high quality grid generation; (3) higher order discretization schemes for low numerical viscosity; and (4) suitable turbulence model. Only when these four tasks are dealt with properly will a computational simulation yield consistently accurate results. Importance of a complete understanding of the relative magnitude, location and source of total pressure losses as the proper basis for original or future design modifications is demonstrated. Agreement between predicted and measured results was found to be good and, just as importantly, very consistent.