Preheat oven to 350°F. Spray 3 - 8 in. round baking pans with vegetable pan spray.
In medium bowl, combine flour, cocoa, baking soda and baking powder. In large bowl, beat eggs, sugar, and vanilla until smooth and creamy, about 3 minutes. Reduce speed to low; beat in mayonnaise and orange zest. Add flour mixture in 3 additions alternately with water, beginning and ending with flour mixture. Pour into pans.
Bake 30-35 minutes or until cake springs back when touched lightly in center. Cool in pans on cooling grid 10 minutes. Remove from pan and cool completely.
Makes about 12 cups batter.