We wish to investigate the giant magnetoelastic transition of Ba3BiIr2O9, which shows an extremely rapid, large (1%) and anisotropic volume increase on cooling through a critical temperature T = 72 K, and isostructural Ba3BiRu2O9. The volume increase is driven by a 5% increase in the Ir-Ir bond length at T, and is accompanied by a sharp drop in magnetic susceptibility. We believe the most likely explanation is the opening of a spin-gap, where the observed rapid decrease in susceptibility is related to the formation of local spin singlets (dimers). We previously collected TOF INS data for Ba3BiIr2O9 and Ba3BiRu2O9 on IN4, observing a spin-gap signal for the Ru compound at 33 meV. We now wish to explore this feature in greater detail and search for the gap in Ba3BiIr2O9, which ab initio calculations indicate should have approximately half the energy. We also wish to search for evidence of a magnetoelastic wave associated with the phase transition.