Make cake according to directions, make 2 (8") layers,
cool, slice each layer in half making 4 layers.
Blend together sugar, coconut and sour cream.
Chill for about an hour.
Spread all but 1 c. of mixture between the layers of cake.
Blend the remaining cup of icing with 11/2 c. of cool whip.
Spread on top and sides of cake.
Seal in airtight container and refrigerate for 3 days before serving.