"The drastically different expansion/contraction rates of the dissimilar metals cause major head gasket problems, and the engine needs to be designed to deal with that situation as it's developed as a prototype."
Jerry, I encountered whay you describe on a 1988 Nissan Sentra. When I pulled the head (aluminum head and iron block) I found that the block and head were still perfectly flat but the head gasket had simply worn out from the differential thermal expansion. It took about 180,000 miles and almost 20 years for that to happen.
Because it took so long for the problem to show up, I'm not overly worried that my street rod that accumulates about 2000 miles per year will be affected in my lifetime. I see aluminum heads on a lot of iron blocks in street rods around here. Nobody has mentioned any head gasket problems.
As for shedding heat into the cooling system, my research indicated that is dealt with by creating a compression ratio about one point higher than would be used on the same engine with iron heads. I set my engine up with 9.0 compression and it runs fine on 89 octane, even in the hottest weather around here, about 100 degrees in August.
In any event, I went for the aluminum heads for a cost savings over totally reworking OEM iron heads, avoiding the labor of bowl blending that I have found takes me about 20 hours, weight savings and the undeniable cool appearance of an all aluminum top end.
I'm a geologist, not an engineer or master mechanic so I went with my research and time will tell. So far, after about 7 years and 15,000 miles it's working out OK. I would be interested in hearing about the long term experience of aluminum heads from other Stovebolters.
