Preheat oven to 325 degrees. Mix flour, sugar, baking powder, and salt. Beat in oil, egg yolks, and water with a spoon until smooth. In a separate bowl, beat egg whites and cream of tartar until stiff peaks appear. Pour egg yolk mixture gradually over the egg whites; folding just until blended. Pour into ungreased 10×4-inch tube pan. Bake 75 minutes or until top springs back. Invert pan on funnel until cake is cool.