Combustion efficiency is a crucial parameter for assessing the quality of fuel-to-heat conversion in Diesel engine combustion. Improving combustion efficiency is essential for boosting engine power, increasing fuel economy, and reducing exhaust emissions. This research seeks to optimize the helical intake manifold design (the outer profile of the cylinder head) in the Vikyno RV165–2 diesel engine to enhance the vortex formation within the engine cylinder. Four different design options will be evaluated for the helical intake manifold (HIM) profile: model 1 - current model, model 2 - increased length with the same intake throat diameter, model 3 - increased bore diameter of the HIM only, model 4 - reduced inlet diameter with increased manifold length. The vortex characteristics of the airflow entering the engine cylinder will be analyzed using Ansys ICE simulation software. The research resulted in the development of a novel HIM geometry (model 2), which average increased the swirl ratio by 15.2% (from 570CAD to 688CAD, where CAD denotes Crank angle) and the tumble ratio by 11.27% (at 690CAD) compared to model 1. These findings provide the groundwork for improving the intake system of the RV165–2 engine.