A turbocharger having a sliding piston for regulating exhaust gas flow into the turbine wheel includes a set of fixed vanes mounted on a fixed first wall of the turbine nozzle and projecting axially toward an opposite second wall of the nozzle, and a set of moving vanes mounted on the end of the piston and projecting in an opposite axial direction toward the first wall of the nozzle. The two sets of vanes are circumferentially staggered relative to each other and overlap each other, the degree of overlap depending on the piston's axial position. The turbine wheel can be a splittered turbine wheel having long blades alternating with shorter blades.