1. Adjust rack to lower-middle position and heat oven to 325 degrees. Whisk sugar, flour, baking powder, and salt together in large bowl (at least 4-quart size). Whisk in two whole eggs, five egg yolks (reserve whites), oil, orange juice and zest until batter is just smooth.


2. Pour reserved egg whites into large bowl; beat at medium speed with electric mixer until foamy, about 1 minute. Add cream of tartar, increase speed to medium-high, then beat whites until very thick and stiff, just short of dry. With large rubber spatula, fold whites into batter, smearing in any blobs of white that resist blending with flat side of spatula.


3. Pour batter into UNGREASED large tube pan (9-inch diameter, 16-cup capacity). Bake cake until wire cake tester inserted in center comes out clean, 55 to 65 minutes. Immediately invert pan to cool. Let cake hang until completely cold, about 2 hours.


5. To unmold, turn pan upright. Run frosting spatula or thin knife around pan's circumference between cake and pan wall, always pressing against the pan. Use cake tester to loosen cake from tube. For one-piece pan, bang it on counter several times, then invert over serving plate. For two-piece pan, grasp tube and lift cake out of pan. Loosen cake from pan bottom with spatula or knife, then invert cake onto plate.