Preheat oven to 180 degrees C. Grease and flour a 23cm ring tin.
Cream butter or margarine and 1 cup sugar. Add eggs and beat well with an electric mixer at medium speed. Mix in sour cream and vanilla. Combine flour and bicarb soda: add to creamed mixture, blending just until moistened. Stir in raisins, walnuts and orange zest. Mix well. Pour batter into prepared pan.
Bake for 60 minutes, or until a wooden pick comes out clean. Cool cake in pan for 5 minutes.
Dissolve 1/2 cup sugar in orange juice. Pour over hot cake. Cool completely in pan.