Heat oven to 325. Lightly grease an 18 cup tube pan. For streusel: In a medium bowl, stir brown sugar, flour, butter and cinnamon with a fork, or rub mixture with fingertips until crumbly. Stir in walnuts. For cake: With an electric mixer on high speed, beat butter, pancake syrup, brown sugar, vanilla, baking powder, baking soda and salt in a large bowl until blended (mixture will look curdled). Add eggs, one at a time, beating well after each (mixture still looks curdled). With mixer on low speed gradually add flour, beating just until blended and smooth. Spoon half of the batter into prepared pan. Sprinkle with half the streusel. Pour in remaining batter and spread evenly. Sprinkle with remaining streusel. Bake for 1 hour, 15 minutes to 1 hour 25 minutes or until a pick inserted in center of cakes comes out with moist crumbs clinging to it. Cool in pan on a wire rack for 15 minutes. If necessary, run a thin sharp knife around edge of pan to loosen cake. Place cookie sheet over pan and carfully invert both. Remove pan. Place rack over cake and turn cake streusel side up. Cool completely. Store wrapped airtight up to 3 days at room temperature or freeze up to 3 months.