The urgent need to reduce green house gas emissions from the transport sector, particularly from heavy-duty trucks, has underscored the importance of developing more efficient internal combustion engines. Using computational fluid dynamics (CFD), this work investigated the impact of valve seat geometry on in-cylinder swirl, addressing a gap in research. Additionally, the suitability of steady-state simulations for providing valid qualitative data on port flow was assessed. To answer both research questions, two approaches were followed: steady-state port flow RANS simulations, and transient RANS simulations in a running engine setup. The results from the steady-state simulations highlighted the limitations of this approach to qualitatively predict swirl, as this quantity is highly dependent on the mesh. Despite these limitations, the steady-state simulations were still able to capture the trade-off between swirl and discharge coefficient, outlined in the literature. Transient simulations revealed that in-cylinder swirl is affected by the geometry of the valve seats. It was found that valve seats that direct the flow towards the liner, while avoiding strong flow separation tend to promote higher swirl, whereas valve seats that induce strong flow separation lead to lower swirl ratios. Despite the trade-off between swirl and volumetric efficiency, the volumetric efficiency losses were found to be practically negligible. The study emphasizes the need for a more comprehensive set of simulations, including more valve lifts and pressure ratios. Given the unsuitability of the steady-state simulations to predict swirl trends, future investigations should focus on replacing this approach by transient simulations with steady-state geometry and boundary conditions, properly addressing flow time-dependency at relatively low computational cost, and facilitating validation with experimental data.