The underside of the gasket is exposed to the valve valley, which can draw oil into the intake ports. I remember seeing a NASCAR race at Talladega where one of the cars would blow a 100-foot long plume of oil smoke on caution laps, and then clear up at speed. Some sneaky crew chief had built in an intentional air leak to cheat on the restrictor plate rules. I did something similar on my claimer engines by drilling holes in the Allen bolts that held the carburetor adapter to the intake manifold, allowing a little air to bypass the 350 CFM 2-barrel Holley carb.
Jerry
