A turbocharger configured to receive an exhaust gas stream from an engine, and input air from an air source, comprising: a turbocharger housing including a turbine housing and a compressor housing; and a rotor configured to rotate within the housing along an axis of rotor rotation, the rotor including an axial turbine wheel, a compressor wheel, and a shaft extending along the axis of rotor rotation and connecting the turbine wheel to the compressor wheel; wherein the turbine wheel and the turbine housing form a turbine configured to extract energy from the exhaust gas stream, and to thereby drive the rotor in rotation around the axis of rotor rotation; wherein the compressor wheel and compressor housing form a compressor configured to compress the input air into the pressurized air stream when the rotor is driven in rotation around the axis of rotor rotation by the turbine wheel; wherein the engine is configured to operate over a range of standard operating conditions; wherein the turbine wheel is configured with a hub, and with a plurality of axial turbine blades configured to drive the rotor in rotation around the axis of rotor rotation when the turbocharger receives the exhaust gas stream from the engine, the blades having an axially upstream edge, an axially downstream edge, a hub end, and a tip end opposite the hub end; wherein the engine exhaust gas stream has gas-specific attributes including a specific gas constant (R sp) and a Boltzmann constant (k); wherein the axially upstream edges of the turbine wheel blades define a turbine wheel inlet, the turbine wheel inlet having an area; characterized in that; the turbine housing forms an inwardly spiraling turbine primary-scroll passageway which has a primary-scroll inlet port which has a centroid that is radially external to the axially upstream ends of the blades; wherein the primary-scroll inlet port is further characterized by an area (a i); wherein the combined turbine housing and turbine wheel are characterized by a primary-scroll radius ratio (r r) defined as a radius of the hub at the axially upstream edge of the blade, divided by a radius of the centroid of the primary-scroll inlet port; wherein the combined turbine housing and turbine wheel are further characterized by a corrected mass flow rate surface density at the primary-scroll inlet port when driven at a critical expansion ratio (E cr); wherein, and this in order for the turbine to produce substantially no axial load on the rotor, the primary-scroll radius ratio (r r) and the primary-scroll inlet port area are sized such that the corrected mass flow rate surface density at the primary-scroll inlet port when driven at the critical expansion ratio (E cr) is greater than a critical corrected mass flow rate surface density (D cr); and wherein the values of D cr and E cr are determined by the equations D cr = r r 101325 288 R sp 1 − k − 1 r r 2 k + 1 1 k − 1 2 ⁢ k k + 1 and E cr = k + 1 2 k k − 1; and wherein, and this in order for the compressor to produce substantially no axial load on the rotor, the compressor is a dual-path parallel radial compressor. a turbocharger housing including a turbine housing and a compressor housing; and a rotor configured to rotate within the housing along an axis of rotor rotation, the rotor including an axial turbine wheel, a compressor wheel, and a shaft extending along the axis of rotor rotation and connecting the turbine wheel to the compressor wheel;