An assembly can include a turbine wheel; a turbine housing that includes a lower turbine housing surface that extends from an exhaust volute to a cylindrical surface that defines an upper portion of a turbine wheel space; a shroud component that includes a contoured surface disposed between an inner end of an upper shroud component surface and an inner end of a lower shroud component surface where the contoured surface defines a lower portion of a turbine wheel space; and a seal mechanism where the turbine housing and the shroud component form an axial gap between a lower axial position of the cylindrical surface and an upper axial position of the contoured surface where the axial gap is axially positioned between an axial position of an inducer portion of the turbine wheel and an axial position of an exducer portion of the turbine wheel.