I have a 6 pack style hood on my car & I dont or haven't yet tried to seal it up. However I have tried 4 different air cleaner assemblys & lost over a tenth when I went from a 14 inch round 2 inch high to a small thin style with an open top. So to add to what Bill is asking. Could it be that the larger air cleaner helped fill the hole & reduce turbulence or is something else going on.