The interest in URANS/LES hybrids, for the simulation of turbulent flows in Internal Combustion Engines, is consistently growing. An increasing number of applications can be found in the specialized literature for the past few years, including both seamless and zonal hybrid formulations. Following this trend, we have already developed a DES-based zonal modeling technique, which was found to have adequate scale-resolving capabilities in several engine-like reference tests. In the present paper we further extend our study, by evaluating the effects of the underlying turbulence model and of the grid quality/morphology on the scale-resolved part of the flow. For that purpose, we consider DES formulations based on an enhanced version of the k-g URANS model and on the URANS form of the popular RNG k-e model. The simulated test cases include a static intake valve geometry and a reference reciprocating piston/cylinder assembly. All the numerical predictions are assessed against the available experimental datasets and with previous computational studies made by other research groups.