Mix the sour cream into the biscuit mix, using a pastry blender or two table knives, until mixture is crumbly. Add 7-Up all at once, stir quickly with a large fork.
Turn out onto lightly floured board and quickly knead 6-8 times. Don't overmix or biscuits will be tough. Pat into a square and cut into about 18 equal pieces using a knife dipped in flour. Can also use a 2 to 3-inch biscuit cutter.
Preheat oven to 400° and cook biscuits for about 7 minutes or until golden.