I guess I didn't lay on the sarcasm enough. Heat management, lol.
Yeah, "heat management" was a lousy choice of words since it sounds like I was implying that the Al blocks would dissipate less heat than the Fe blocks, or something to that effect. Obviously that isn't going to happen, since Al has a thermal conductivity of ~3X that of cast iron. The point that I was trying to make (rather poorly, it seems...) is that the Al blocks are more likely to be adversely affected by long term exposure to heat than Fe blocks are. More specifically, the deck surface of the Al block is more likely to warp than a similar Fe block would under similar conditions, IMO. I'm not talking about structural failure here, but just enough warpage/distortion of the deck surface to cause head gasket problems after many thousands of miles, for example.
Obviously the Al blocks can stand the stresses of 1000+ hp engines for short periods of time, at least. But can they tolerate opertaing under stress at high temps for long periods of time without warping enough to cause head gasket problems? I dunno, but it wouldn't surprise me if deck surface warpage was an issue with the existing Al blocks that a simple switch to Fe blocks made "good enough" to pass Ford's durability tests. It might not be the ideal solution (especially for a car that is already too heavy), but it just might have been "good enough" in Ford's eyes to pursue. I have no doubt that the reduced cost of the iron blocks made the bean counters *very* happy, but I still suspect that cost wasn't the only issue. Only Ford knows for sure.