As the climate change is influenced by fossil fuels burning cars, the emissions of exhaust fumes should be reduced. Therefore the usage of twin-scroll-turbochargers which uncouples the exhaust flow of specific cylinders from each other is essential. However, the requirements and specifications for the production process are more complex than for the previously produced turbochargers. This represents a challenge for the development and production process, because established standard casting process procedures are not directly applicable any more. This master thesis is concerned with the quality and process optimization of the steel casting process for new twin-scroll-turbocharger housings involving complex core technology. The requirements of the sand cores during the steel casting process are to reproduce the complex geometry accurately, as well as, to prevent veins, cold runs and gas emissions from the core. Sand additives can help to prevent these casting defects. By intelligent selection of organic and inorganic components it is possible to create an effective antidote against veining. However, the effects of additives are not limited to this specific casting defect. Their effect on geometric accuracy and emissions of gas has to be considered as well. For that purpose a quality study with nine different additives of the inner sand cores for two types of turbocharger housings was initiated. In total about 1200 housings were produced and investigated for the study. The quality of the sand cores at the core shooting machine as well as an analysis of the casting defects after the fettling shop were monitored. With this approach it was possible to monitor the whole production process and to obtain conclusions on the effectiveness of the additives. Additionally, the geometric accuracy of the cast was measured via an optical measurement system. The reference for any comparison was the currently used standard sand additive. In addition, all sand additives were investigated to elucidate their ingredients and behaviour with temperature. Research was conducted on core sand and core samples. Their specific mechanical strengths and stiffness as well as their expansion properties were determined. These investigations helped to understand the results of the quality study and specifically the veining mechanism.