Cut squash in half; discard seeds and membrane. Place squash halves, cut sides down, in an 11- x 7-inch baking dish. Add water to a depth of 1/4 inch.
Bake at 375° for 35 to 45 minutes or until tender; cool slightly.
Scoop out and mash pulp; discard shells.
Toss together 1/4 cup flour and raisins. Set aside.
Combine remaining 2 1/2 cups flour, cinnamon, nutmeg, and cloves; set aside.
Combine squash pulp, sugar, and next 3 ingredients; stir in flour mixture until blended. Stir in raisins. Pour into a 12-cup Bundt pan coated with vegetable cooking spray.
Bake at 350° for 45 minutes or until a wooden pick inserted in center comes out clean. Cool in pan on a wire rack 10 minutes. Remove from pan, and cool completely. Sprinkle with powdered sugar, if desired.