The Variable Intermeshing Clearance (VIC) mixer possesses the unique feature of the ability to change the inter-rotor clearance during the compounding process. To improve the mixing performance of the VIC mixer new designs are proposed. A fluid dynamics analysis package-FIDAP, using the finite element method was employed to simulate the flow behavior in the VIC mixer. The problem of time dependent flow boundaries was solved by selecting a number of sequential geometries with 20 degree increments to represent a complete mixing cycle. Dispersive mixing was evaluated in terms of both the shear stress distribution and the elongational flow components generated in the flow field. Distributive mixing was studied numerically by means of tracking the evolution of particles originally gathered as clusters. Our studies indicate that the new design of an enlarged chamber gives overall better dispersive and distributive mixing performance than the traditional VIC. The VIC mixer with both an enlarged chamber and wider rotor blades design shows poorer dispersive mixing but better distributive mixing capability. The effect of inter-rotor clearance on mixing efficiency is also discussed.