The focus of this work is to determine the limitations of grain refinement and modification of hypoeutectic Al-Si-Cu castings alloys as well as relevent influencing factors. Investigations are made both in production environment and under laboratory conditions. The measurement and interpretation of the influencing factors of the grain refinement and modification are very essential, since they can affect the expected properties of the cast parts significantly. Therefore, thermal analysis, metallographic examination methods and spectral analysis are used as basic measuring methods. The first section focuses on the activation time and the fading of different grain refiners (AlTi5B1, AlTi3B1 and Tibloy) under laboratory conditions. Other topics include the activity of the grain refiners after re-melting and re-casting as well as the effect of the grain refinement and modification after blending of primary metal and returns in different proportions to each other. The results confirm all three grain refiners to be active within a few seconds. The best fading performance shows the grain refiner AlTi5B1. The fact that after the re-melting the effect of the grain refiners subside completely is not observed at very high blending ratios of primary metal to returns. In the second section of this work, the influencing factors were developed under production conditions. Here, the amounts of grain refiners and modifier additions, the holding and pouring temperature as well as the holding time of the melt in the holding furnace are varied. The experiments show, however, that only the additions of grain refiners influence the casting properties verifiably.