Cylinder head aluminium v Iron

[Bob Culver]

All else equal, alloy heads enabled higher cr before pinging became a problem. (on the likes of sv V8 about 1 ratio advantage) On a Seven with either material breathing considerations limit cr to below where pinging becomes a problem. Heat loss from the combustion can be less with iron.
Iron heads are certainly resilient. Decades and 150000 miles ago I ran my iron head Hillman at 60 mph for miles dry . Added water boiled 15 minutes later! No effect. The same engine with alloy head was notorious for blown gaskets.