Preheat the oven to 325F.
In a medium sized bowl, add the cake flour, sugar, baking powder and salt. Whisk together and form a well in the middle. Add the egg yolks, oil, juice, zest and vanilla and set aside.
In a large bowl, add the egg whites and cream of tartar. Using a handheld mixer, beat the egg whites until stiff.
Using the same handmixer/beaters, mix together the egg-flour-orange bowl until smooth.
Fold the egg yolk batter into the bowl of egg whites, 1/4 at a time.
Pour into an ungreased 12" angel food/tube cake pan. Bake in the preheated oven for 1 hour, or until a toothpick comes out clean when inserted. Invert pan while cooling. Remove from pan.
To make the icing: In a large mixing bowl, beat together all frosting ingredients until smooth. Frost cake all around and serve.