A two stage radial compressor assembly comprising: first and second radial compressor wheels assembled in a hub-to-hub orientation; an annular baffle comprising: an outer edge; and a substantially parabolic portion that comprises an inner edge that defines an opening having a central axis; and opposing surfaces that extend from the inner edge, wherein one of the opposing surfaces comprises an annular notch adjacent to the inner edge wherein the annular notch is defined in part by a radial notch width, wherein: one of the opposing surfaces comprises a low pressure surface portion to one side of the inner edge for facing a hub portion of a first radial compressor wheel and the other of the opposing surfaces comprises a high pressure surface portion to the other side of the inner edge for facing a hub portion of a second radial compressor wheel, and wherein one of the opposing surfaces comprises a first substantially semi-parabolic shape and wherein the other of the opposing surfaces comprises a second substantially semi-parabolic shape wherein a radial offset between ends of the opposing surfaces defines the radial notch width; and the annular baffle and the hub portions of the compressor wheels (244-1, 244-2) define at least in part a passage that causes the flow of gas therethrough to bend. first and second radial compressor wheels assembled in a hub-to-hub orientation; an annular baffle comprising: an outer edge; and a substantially parabolic portion that comprises an inner edge that defines an opening having a central axis; and opposing surfaces that extend from the inner edge, wherein one of the opposing surfaces comprises an annular notch adjacent to the inner edge wherein the annular notch is defined in part by a radial notch width, wherein: one of the opposing surfaces comprises a low pressure surface portion to one side of the inner edge for facing a hub portion of a first radial compressor wheel and the other of the opposing surfaces comprises a high pressure surface portion to the other side of the inner edge for facing a hub portion of a second radial compressor wheel, and wherein one of the opposing surfaces comprises a first substantially semi-parabolic shape and wherein the other of the opposing surfaces comprises a second substantially semi-parabolic shape wherein a radial offset between ends of the opposing surfaces defines the radial notch width; and the annular baffle and the hub portions of the compressor wheels (244-1, 244-2) define at least in part a passage that causes the flow of gas therethrough to bend. outer edge; and a substantially parabolic portion that comprises an inner edge that defines an opening having a central axis; and opposing surfaces that extend from the inner edge, wherein one of the opposing surfaces comprises an annular notch adjacent to the inner edge wherein the annular notch is defined in part by a radial notch width, wherein: one of the opposing surfaces comprises a low pressure surface portion to one side of the inner edge for facing a hub portion of a first radial compressor wheel and the other of the opposing surfaces comprises a high pressure surface portion to the other side of the inner edge for facing a hub portion of a second radial compressor wheel, and wherein one of the opposing surfaces comprises a first substantially semi-parabolic shape and wherein the other of the opposing surfaces comprises a second substantially semi-parabolic shape wherein a radial offset between ends of the opposing surfaces defines the radial notch width; and the annular baffle and the hub portions of the compressor wheels (244-1, 244-2) define at least in part a passage that causes the flow of gas therethrough to bend. one of the opposing surfaces comprises a low pressure surface portion to one side of the inner edge for facing a hub portion of a first radial compressor wheel and the other of the opposing surfaces comprises a high pressure surface portion to the other side of the inner edge for facing a hub portion of a second radial compressor wheel, and wherein one of the opposing surfaces comprises a first substantially semi-parabolic shape and wherein the other of the opposing surfaces comprises a second substantially semi-parabolic shape wherein a radial offset between ends of the opposing surfaces defines the radial notch width; and the annular baffle and the hub portions of the compressor wheels (244-1, 244-2) define at least in part a passage that causes the flow of gas therethrough to bend.