Following a review of cubic equations-of-state (EoS), a new identity linking the heat of vaporization, for pure components, to the EoS is derived. The identity is applied to simple cubic EoS to allow tuning of both the attraction (a) and repulsion (b) constants to experimental vapor pressures and heats of vaporization at subcritical temperatures. These new tuning procedures are compared with previous procedures for benzene and for methanol. The results show marked improvements to the point where the simpler Redlich-Kwong EoS provides better results with our procedures than does the usually superior Peng-Robinson EoS with conventional procedures.