We investigate the impact of the star formation efficiency in cluster-forming-cores (i.e. local SFE) on the evolution of the mass in star clusters over the age range 1-100Myr, when star clusters undergo their infant weight-loss/mortality phase. Our model builds on the N -body simulation grid of Baumgardt & Kroupa (2007). Assuming a constant formation rate of gas-embedded clusters and a weak tid...