1Move oven rack to lowest position. Preheat oven to 325 degrees. In large bowl, sift cake flour, 1 1/4 cups sugar and baking powder; set aside. In separate bowl, mix oil, egg yolks, orange juice and orange peel together; set aside.
2In mixer bowl, on medium speed beat egg whites with cream of tartar until foamy. On high speed,continue beating until soft peaks form. (Soft peaks are reached when the peaks drop when beaters are lifted). Gradually add sugar until firms peaks form. (Sugar needs to be added slowly so it will dissolve and not weigh down the meringue. Whites should look glossy when beaters are lifted. The tip of the peaks will pull back slightly but still hold).
3Beat flour mixture and orange juice mixture until well blended. Fold in egg whites. Gently pour batter into a 10" tube pan. Using a rubber spatula, smooth and level top of cake. Gently tap the pan against the kitchen counter to remove any large air bubbles. Bake for 50 to 55 minutes or until cake springs back when lightly touched. Immediately invert pan. Cool Completely (about 1 hour). To remove cake, run a knife against the sides of the pan. Turn out on a plate. Then run the knife in one swift motion around the base of the pan. Allow the cake to gently fall onto the plate. Glaze cooled cake.
4Beat butter and powdered sugar until smooth. Add orange peel and orange juice. Beat mixture until blended. Drizzle glaze over cooled cake.