Preheat oven to 325°.
Combine sugar, oil, eggs, and vanilla in a large bowl and beat for 1 minute at medium speed of an electric mixer.
Combine 2 ½ cups flour, baking soda, salt, and cinnamon.
Gradually add flour mixture to sugar mixture, beating at low speed of electric mixer until blended.
Toss apples with remaining ½ cup flour and fold into batter.
Spoon batter into a greased and floured 10" bundt pan.
Bake at 325° for 1 hour and 30 minutes or until wooden pick inserted into center comes out clean.
Cool in pan for 15 minutes.
Remove from pan onto wire rack and let cool completely. Sprinkle with powdered sugar.