The purpose of the present work was to bring further improvements to the simulation of the crystallization process in terms of morphology and crystallinity in quenched slabs of isotactic polypropylenes (i-PP). Incorporation of the temperature dependence of specific heat, density, and thermal conductivity into a previous simulation program based on their constant values does not influence the predicted results. A new approach to calculate the nuclei concentration to obtain the gapwise distribution of spherulite diameter was proposed and tested. A microthermocouple was placed in the PP slabs to follow the crystallization process during their quenching. The temperature traces as a function of time were measured. With this technique, it was possible to determine the correct heat transfer coefficient and the induction time for crystallization at high cooling rates relevant to injection molding. The present results indicate an importance of the decrease of the heat release during crystallization at high cooling rates.