In-cylinder flow in diesel engines plays an important role in the combustion, thus affecting the emissions from the engine. Swirling flow inside the cylinder during intake and compression stroke is one of the important parameters that improve combustion. This paper deals with comparison between two different intake manifold geometries in a direct injection diesel engine in terms of their swirl generation mechanisms in the cylinder during suction stroke. The modified geometry involves a twisted tape inserted in the intake manifold for swirl generation. A three-dimensional numerical study of the flow behavior is performed using Computational Fluid Dynamics (CFD) and experimentally validated using a steady flow test bench. The effect of twist ratio on the swirl generation is simulated using CFD. The CFD study involves a transient case applied to a dynamic mesh which characterizes the downward movement of the piston during suction stroke. The in-cylinder swirl is generally characterized by swirl coefficient and swirl ratio. These parameters are evaluated to understand the effect of twisted tapes and their geometries in the intake manifold of a diesel engine. An experiment is also performed with the initial and modified manifold geometry to understand the emission characteristics of the diesel engine. © 2013 SAE International.