Heat oven to 350 degrees.In a large bowl, stir together the dry cake and the entire can of crushed pineapple with its juice. Stir well until all the dry mix is incorporated. (The mixture will get really foamy.)Pour the batter into a 9x13 pan. (DO NOT GREASE THE PAN.)Bake at 350F degrees for time specified on the box for size pan. When the sides pull away from pan and toothpick inserted in the center comes out clean, the cake is done. (About 30-40 minutes for a 9x13-inch pan.)Remove from the oven and place on a wire rack to cool.