Hi peter, the cobra oval air cleaner is not worth a damn as far as breathing is concern. the 14" is the best all around. After installing my PI manifold I did not have enough clearance between the hood and the carb to even use the Ford 14" filter. I installed a 1960's GM unit which cam stock on BB 66 to 71 Corvettes, Chevelles, etc. It's the lowest 14" air cleaner I have seen. It's not only the size of the filter but also the height which determines the breathing!
Emmanuel