Root Beer Float Cake II

Preheat oven to 350 degrees F (175 degrees C). Grease and flour a 9x13 inch pan.
In a large bowl, combine cake mix, 1 1/4 cup root beer, oil, and eggs. Beat on low speed until blended. Scrape bowl, and beat 4 minutes on medium speed. Pour batter into prepared pan.
Bake in the preheated oven for 30 to 35 minutes, or until a toothpick inserted into the center of the cake comes out clean. Allow to cool.
To make the frosting: In a large mixing bowl, combine the whipped topping mix and 1/2 cup root beer. Beat until soft peaks form. Spread on top of cake.