Estimation of the percentage of cold gas with ϵ_g > 0 converted into stars during the replacement of the inner gas disk, which preceded the formation of the gas-versus-stars counter-rotating disks, for all the studied galaxies. We also show the variations with respect to the stellar mass of the main galaxies (upper panel), the gas fraction f_gas (middle panel) and V_∗/σ, all quantities estimated just before the retrograde gas accretion phase. f_gas and V_∗/σ have been estimated both within one effective radius but the same trends are obtained when estimated within 5 R_e. These plots first suggest that, during the removal of the pre-existing gas, on average, a higher fraction of cold gas is converted into stars rather than being expelled. Secondly, there is a clear correlation between the percentage of gas converted into stars and V_∗/σ. The original morphology of galaxies therefore seems to impact the efficiency of the star formation during the compaction of the central gas component.