Summary form only given. Magnetohydrodynamic simulations provide a powerful tool for improving our understanding of the complex physical processes underlying the behaviour of wire array Z-pinches. We show how, by using a combination of high resolution 3D simulations of a single wire in an array along with lower resolution simulations of the array as a whole, it is possible to encompass all of the important features of the wire ablation, implosion and stagnation phases and to observe how these phenomena control the X-ray pulse that is achieved. Comparison of code results with experimental data from 'Z', MAGPIE and other pulsed power generators is shown to provide a detailed benchmark test for the models. Predictions for the X-ray performance of future machines can then be made along with the dependence on maximum current and rise-time. The design of novel array configurations also allows improvements to implosion symmetry and X-ray rise- time, and more compact radiation sources to be investigated.