A compressor housing is provided for a compressor impeller. The compressor housing comprises an outer shell including an outer section, a midsection, and a center section. The midsection of the outer shell forms an upper volute wall portion of the compressor housing, and the center section forms an inlet for the compressor housing. A diffuser is also provided that is comprised of a center section, a base section, and an outer section. The center section of the diffuser has a substantially cylindrical outer edge received within a complementary substantially cylindrical mating surface in the outer shell center section. The diffuser base section has a raised first mating projection for engagement with the first mating surface of the midsection of the outer shell. The diffuser outer section has a raised second mating projection for engagement with a second mating surface of the midsection of the outer shell. A back plate is also provided that is formed of a generally circular structure. The diffuser base section has a generally flat lower surface for engagement with a generally flat upper surface of the back plate. The outer shell midsection, the diffuser and the back plate form the volute wall portion of a compressor housing.