Over the last few years, engine development has succeeded in reducing friction by up to 30 %. This corresponds to a reduction of fuel consumption in urban traffic of around 10 %, thus, making friction reduction - aside from the introduction of Otto DI engine and the transition from IDI to DI Diesel engines - an effective measure to reduce fuel consumption.Investigations of engines and engine components show that even today's “Best in Class” engines still harbor a reduction potential of least 20 %. Possible ways to realize this potential lie in: Adapted dimensioning of the friction relevant engine parameters Lightweight design of dynamic components Optimized layout of the timing drive (especially in valve train designs with roller followers and chain drives) Optimization of the piston group (up to 50 % of the parasitic losses can occur here)The investigations are based on detailed friction measurements of over 100 sample engines and their components. The analysis of the measured data, together with more in-depth measurements using special measurement techniques give insight into current trends and directions for new designs. With the help of benchmarking and simulation programs, the influence of individual design parameters on the friction behavior and variants can be found.This paper is meant to highlight the often hidden role of engine mechanics in the development of fuel consumption favorable engines and compare it to the development steps of SI and Diesel engine procedures.