Intake manifolds

It helps the engine run smoother in cold weather as it warms up. If you see fuel piddling from the boosters after you turn off the engine, or you can't hold your hand on the carb after the engine warms up, then you may have fuel percolation issues which can be rectified by blocking the cross-over. If you live in warmer climates, or only drive your car in the summer, you probably don't need the extra heat.