Hi Drof,You really didn't give much info as to why you are interested in posted vs non posted heads. For stock ECZ G heads, the shape of the combustion chamber and ports is the same for posted or non posted heads. So for more or less stock performance, non posted heads are just as good posted. But if you are building a high performance engine especially one with high combustion pressures (that is to say High Compression or supercharged applications) then posted heads are prefered. Also with Y's, especially smaller displacements of say 300CID or less, and flat top pistons, it is difficult to build much compression without radical head milling. The posted heads are very applicable in this case because when the head surface is thinned down a large amount (say over .050") the head gets weak and head gasket leaks start to happen. But posted heads are less likely to be weak when milled a large amount.