This work presents a phenomenological analysis of a minimal nonlinear gravitational model applied to a subset of disk galaxies from the SPARC database.The model introduces a single characteristic acceleration scale g* through a nonlinear modification of the Poisson equation, without invoking explicit dark matter halos. The fitting of six galaxies with heterogeneous morphologies (UGC 128, NGC 3198, IC 2574, DDO 154, NGC 6503, NGC 2403) yields acceleration scale values in the range (0.55–1.73) x 10^-10 m s^-2, with mean value (1.10 ± 0.46) x 10^-10 m s^-2. The relative stability of this parameter suggests the emergence of a universal dynamical scale governing the asymptotic behavior of galactic rotation curves. A possible phenomenological connection between the fitted acceleration scale and the cosmological quantity cH0 / (2pi) is discussed. The analysis remains strictly dynamical and does not claim a complete relativistic or cosmological theory. The work is intended as a preliminary phenomenological contribution to the study of flat galactic rotation curves and the possible existence of an intrinsic acceleration scale.