1Preheat oven to 350 degrees F (175 degrees C). Lightly grease one 9x13 inch cake pan or one 10 inch bundt pan.
2In a large bowl stir together; lemon cake mix, lemon instant pudding, water, oil, eggs, and 5 tablespoons key lime juice, mixing well. Pour batter into prepared pan.
3Bake at 350 degrees F (175 degrees C) for 45 minutes. Pour key lime glaze over cake while still warm.
4To Make Glaze: Mix together the confectioner's sugar and 3 tablespoons of the key lime juice (or more if necessary), spoon glaze over warm cake.