For the lightest, tenderest, and highest cakes ever, use 7-Up as the liquid with your favorite cake mixes. Try it with chocolate, yellow, white, angel food, or devil’s food mixes.
From You're Really Cooking When Your Cooking With 7-Up, 1957
Substitute the recommended liquid on the instructions with the same amount of 7-Up.
Continue preparing cake as directed by the package instructions.