Preheat oven to 350ºF. Grease and flour a 10-inch fluted tube pan. Set aside.
In a large bowl, beat sugar and butter with electric mixer on medium speed until mixture is light and fluffy. Add eggs; beat well. Beat in sour cream and vanilla just until combined.
In a small bowl combine flour, baking powder, and salt. Beat into creamed mixture until combined. Pour half of the batter into prepared tube pan.
In a small bowl stir together pecans, brown sugar, and cinnamon. Sprinkle 1/2 cup of the nut mixture on top of batter in pan. Carefully spread remaining batter on top of nut mixture. Sprinkle with remaining nut mixture; press lightly into batter.
Bake in a 350º F oven for 45 to 50 minutes or until a wooden toothpick inserted near the center comes out clean.
Remove cake from oven; cool for 5 minutes. Invert cake onto a serving plate. Cool 15 minutes more. Dust with powdered sugar. Serve warm or cool.