Hi, it's just a case of first putting a straight across ( 1-5 ports) the ex. manfold then see if it's flat, if it's warped take it to a local engineering firm & see if they can skim it for you (my Son & I had both ours done £40 each). The hardest part was finding someone who could clamp it at the correct angle for skimming due to it's odd shape or you can buy them skimmed & de-webbed on flea bay. We didn't cut through our webs.