Sift flour, sugar, baking powder and salt 3 times into a large bowl.
Open a well in the center and place egg yolks, orange peel, oil and orange juice.Fold gently with a rubber spatula, until thoroughly combined.
Whip egg whites with cream of tartar until soft peaks form. Add sugar, gradually and continue beating until stiff peaks form (as for meringue).
Pour yolk mixture over beaten egg whites and fold gently until combined.
Transfer to an ungreased chiffon pan and bake in oven 325°F (170°) for 55 minutes. Raise temperature to 350°F (180°) and bake chiffon 10 more minutes.
Remove from oven and cool on a rack, upside down.