Method for producing a turbine housing and the turbine housing

Objective of the turbine housing (2) made of cast according to the present invention is to realize a simple configuration capable of reducing the ventilation resistance and to enhance the efficiency of the exhaust gas turbocharger. From the axis of the turbine Ye Lun (K) of the shroud portion (23) of the radial distance of the front end (23d) set up to R1, scroll to the inner Zhou Duan portion (21) of the hub side wall surface (21c) of ( when the radial distance R2 21d) is set up, satisfying R1 scroll portion (21) of the hub side. Then, the front end than (23d) shroud portion (23) facing radially outward spiral flow passage (12) of the shroud portion (23) and a scroll portion (21) of the passage face (21a, 21b, 21c,) the inner 23a, a predetermined range in the front end (23d) from the shroud portion (23) from the set region a, the region adjacent to the predetermined range a is set areas B, channel surface area a configured roughness smaller than the area B.