Also I've noticed less expansion in valve lash when dealing with oe .. World etc cast heads as opposed to dart Brodix.. ( on adjustable setups)

Maybe less fear of rocker stud breakage with iron when no shaft or girdles are added..

Aluminum is become easier to mass Cnc .. Plus it looks cool

Good thing about aluminum transferring heat faster is the exhaust valve.

I like the weight savings of an aluminum head, but one thing I think about is the expansion rates of aluminum on an iron block vs iron on iron. I have no idea what issues it causes but the rate of expansion between the two are huge, could be a non issue, just throwing it out there. What does it do to head gaskets with the differential?

Agreed. Point in my original post, was that there's more to cooling an exhaust valve, then the cylinder heads material. Things like seat widths, stem clearance, water temps, seat materials etc.

Its like the GM truck and RV engines. For years, they powered huge motorhomes, tow rigs pulling heavy trailers, up mountains. Heat was enough of an issue, that they installed inconel valves in these engines, which were cast iron headed. These engines ran 200+ degree water temps, and even saw 230+ pulling heavy loads, on hot summer days, ingesting 100 degree hot desert air. While they were only maybe making 400-450 ft lbs of torque, there exhaust temperatures had to be extreme. Many of these engines went 200 plus thousand miles in those conditions. They made quite a bit of low rpm cylinder pressure, with tiny camshafts as well. Tons of stock mercury engines running around in boats, everything from iron 4 cylinders, to merc racing supercharged engines, that proved to be extremely reliable.

I've seen some exhaust temperatures from N/A engines making half the power of supercharged , or even other N/A engines , be the same or greater.

aluminum heads on iron block has been done for 50 years so me think it is ok.

A little of topic, but coating a chamber won't cause "heat soak" and pre ignition. Coating valves and piston tops does help keep the heat out of them as you said - this is a good thing.

haxor,if the head gets coated would that make it retain heat and hinder the transfer of heat to the cooling water flowing through the head?

Coating piston tops is designed to reflect or transfer heat.. We have coated skirts to help with scuffing that occurs with short skirt piston. Helps not to scuff cyl walls..

The coating is designed to reflect the heat back in to the chamber to help from losing the energy. It is not designed to retain heat. Transferring excess heat in to the actual head material is often why aluminum heads require more timing advance.

i understand that but my question is----will coating the head in the chamber impede cooling of the chamber?example,throttle,s pinned for 5 minutes in a 42 foot fountain.