In a large bowl with a mixer, beat sugar, eggs, and 1/2 cup oil until well blended, about 2 minutes.
In another bowl, mix flour, baking soda, cinnamon, nutmeg, salt, and cloves. Stir in pears, walnuts, and raisins.
Add flour mixture to egg mixture and stir just until evenly moistened. Spread batter in an oiled and floured 9- by 13-inch pan.
Bake in a 350° oven until top of cake springs back when lightly touched in the center, about 1 hour (about 45 minutes in a convection oven). Cool on a rack. Serve warm or cool; cut into rectangles and lift out with a spatula.