High pressure experiments have been performed by thermobarometric analysis on two compounds of chiral non-symmetric dimesogens, which both exhibit the S-(C) over bar* and S-A mesophases. The pressure-temperature phase diagrams were determined. Molar volume changes for all phase transitions, and the pressure coefficients at constant volume-of the phases were also deduced from the recorded thermobarograms. The thermobarometric analysis allows us to easily separate the entropy of the phase transition into a configurational part and a part dependent on volume.