In large bowl of electric mixer, combine flour, sugars, baking powder and salt. Mix until blended. In another bowl, combine oil, egg yolks, water and maple flavoring. Turn mixer on medium speed. Add liquid ingredients to dry ingredients. Beat 1 minute. In large metal bowl (not plastic), beat egg whites until foamy. Add cream of tartar. Whip at high speed until stiff peaks form. Pour batter over egg whites. Fold together gently until blended. Fold in 1 cup of chopped nuts. Pour into ungreased 10" angel food pan. Bake at 325~ for 55 minutes. Increase oven temperature to 350~. Bake 10 minutes longer until top springs back when touched. Cool upside down. Remove from pan. Bring maple syrup to boil in a medium saucepan. Lower heat. Simmer 15 minutes or until almost reduced to half. Drizzle hot syrup over cooled cake. Sprinkle with toasted walnuts. Decorate with whipped cream.