Make cake: Preheat oven to 325°F. Sift flour, 3/4 cup sugar, baking powder and salt. Separate eggs. Whisk yolks, oil, juice, zest and vanilla. Whisk oil mixture into flour mixture.
Beat whites until frothy. Add cream of tartar; beat until firm. Beat in 3/4 cup sugar, 1 Tbsp. at a time, until peaks form. Fold 1/4 of whites into batter; add remaining whites.
Bake in an ungreased 10-inch tube pan 1 hour and 10 minutes, until a tester comes out clean. Invert pan over neck of a bottle to cool. When cool, run a knife around edges to remove cake. Place on a rack.
Make glaze: Stir juice into sugar; drizzle over top of cake and down sides.