Preparation : Sift dry ingredients together into mixing bowl. Make a well in center of mixture. Add salad oil, egg yolks, water, bananas and vanilla. Beat until smooth. Into large mixing bowl put egg whites and cream of tartar. Whip until very stiff. Do not underbeat they should be stiffer than for angel food or meringue. Gradually pour cake batter over whipped whites. Gently fold until the two mixture are blended. Do not stir. Pour into ungreased tube cake pan. Bake in 325 degrees oven for one hour then increase temperature to 350 degrees for 10 minutes until top springs back when lightly touched. Immediately turn pan upside down let hang in pan until cake is cool. Remove cake from pan and frost with: Cream cheese and margarine well and add vanilla. Beat in sugar a little at a time until of spreading consistency.