Reliability of functionally graded metal matrix composites (FGMMCs) for automotive components is still dependent on the detailed knowledge of the mechanisms of the microstructural build-up, for instance on the mechanisms leading to the distribution and relative positions of the reinforcing particles. In order to assess the influence of the SiC particle size on the 3-D inter-particle connectivity in functionally graded Al/SiCp composites produced by centrifugal casting, X-ray microtomography experiments were performed at the ID19 beamline in ESRF (European Synchrotron Radiation Facility). The FGMMCs consisted of an Al-10Si-2Mg alloy matrix, reinforced by an average SiC particle volume fraction of 0.10; two different average sizes were used: 37 mu m and 12 mu m. The holographic modification of the X-ray CMT (Computer Micro-Tomography) method allowed to obtain neatly contrasted images, as opposed to classical CMT. Good agreement was found between the particle size evaluated by CMT and by laser interferometry. Particle clustering has been evaluated in number and volume, showing that a lower mean particle size is related to more clustering. Such an adverse effect relies on the importance of particle/liquid alloy surface tension. Also, the mean particle size has been evaluated as a function of particle number within a cluster: as expected, the larger a cluster, the larger the particles inside it.