Is there a difference between "ductile iron" and "hardened ductile iron" valve seats? I am planning a big-inch street machine (4.42" x 4.3") with moderate (9.0-9.5) compression and don't know which way to go on the heads. Basically the choice is between a set of D3 iron heads and Edelbrock aluminum versions, both with 95 cc chambers. The D3 heads are on hand, already cut for screw-in studs and for oversize valves. They require a complete port job on the exhausts (including taking off the EGR bosses) plus valve grind, valves, etc etc. The Edelbrock Performer heads are "ready to go" but of course much more expensive. They also feature "ductile iron" seats. Hence my question, is ductile iron the same as hardened ductile iron? If I would have to change to "hardened" exhausts, then the aftermarket heads cost goes up exponentially. Also, any opinions on the quality of the Edelbrock heads, and whether or not hardened seats are even necessary on an engine that will never see hard use on the street?