Whats the advantage of these then? ive seen a couple i think 10mm and 16mm. which is best then?. What improvement do you get and is it just a case of fitting with an inlet gasket eitherside and fit and forget or do it require an tweak to the cars map etc etc??. just asking as im taking the head of my 3 door soon to upgrade to wrc gasket and take it from its current stage 1 spec to about 325 bhp. thanks in advance