A mold and method for gravity casting may integrally cast a turbine housing having a twin scroll unit and a bypass unit and an exhaust manifold having a plurality of exhaust runner units. A turbine housing-side riser may be formed based on the end portion of the twin scroll unit within a first mold and a second mold in the state where the cavity of the turbine housing is formed so that the end portion of the twin scroll unit which is the outlet of the turbine housing is upward disposed.