Progress in Laser powder bed fusion manufacturing has led to greater use of Additive Manufacturing in combustion chambers/nozzles. This allows for the creation of more intricate and efficient solutions, but generates the need for a better understanding of how surface roughness in micro-channels used for engine cooling relates to build angle and performance. The research presented in the framework of this thesis assesses the friction factors and internal surface roughness of 18 additively manufactured channels, through the means of flow testing and microscope inspection. Positive correlations between build angle and friction factors were found, and further investigation revealed relative roughness levels outside the applicability range of Moody charts. Comparison of open and closed contour channels confirmed roughness similarity, providing valuable input for the manufacturing of witness channels in cost/time sensitive applications. Finally, the relation between surface roughness parameters and sand-grain roughness were investigated, revealing their dependency on flow properties.