Preheat Oven to 325 F. Grease 10 inch tube pan; set aside.
In a large bowl, beat 1 1/2 C granulated sugar, 1 C vegetable oil, 2 tsp vanilla, and 2 eggs until well blended. Stir in 2 C chopped peeled tart apples. In another bowl, stir together 3 C flour, 1 tsp ground cinnamon, 1 tsp baking soda, 1 tsp salt, and 1 C chopped walnuts. Add apple mixture to dry ingredients. Stir in just until moistened.
Batter will be thick. Spoon batter into the greased tube pan; spread evenly. Bake in the 325 F oven for 1 hour or until a wooden toothpick inserted in the center comes out clean. Cool cake in pan on a wire rack for 10 minutes. Remove from pan; cool completely on wire rack. Sprinkle powdered sugar over cake.