A previous investigation  has demonstrated the wide variation of grain size found through the cross-section of a Direct-Chill (DC) cast ingot due to the position dependent solidification rate inherent to the process. Recently we have demonstrated  that the use of a turbulent jet as a metal entrance method has the potential to significantly reduce the size and variation in the grain structure. We here report a series of experiments investigating the influence of jet power on the grain size and distribution in Al4.5Cu DC cast ingots. Our findings indicate that significantly increasing the jet power does not appreciably decrease the grain size. Instead, a threshold jet power required for grain refinement is anticipated, beyond which there are only marginal improvements. S.R. Wagstaff, and A. Allanore: Light Metals, TMS, 2015, pp. 877-882 S.R. Wagstaff, and A. Allanore: Light Metals, TMS, 2016, pp. 715-720.