Preheat oven to 325 degrees. Prepare tube pan. Beat egg whites with cream of tartar, set aside. Combine flour, sugar, powder, and salt. Make a well and add yolks, oil, water a nd vanilla. Beat 2 minutes medium speed. Fold in egg whites. Pour into pan, bake 55 minutes. Increase temperature to 350 and bake 10 minutes more. Invert pan and cool completely. Frosting follows.