About the only advantage that aluminum heads have over iron is heat dissipation. Admitably that is a BIG advantage when considering compression ratio, timing flexibility and overall performance. But iron heads have their own set of advantages as well: 1. material stability there-by reducing head gasket problems. 2. no adverse reactions to anti-freeze engine coolants. 3. Generally longer life especially in normal non-competitive, street driving. If you have aluminum heads you should check the bolt torque reqularly and at least change your anti-freeze more often. I believe the three biggest reasons that manufacturers will produce the aluminum heads is because 1. they are cheaper to produce, 2. the market wants them (oh god ya gotta have an aluminum head), 3. The sanctioning bodies allow them. One last commentary, I had a new engine built a few years ago ,by a professional race engine builder, for my '70 Vette. It is a roller cam, roller rocker, 383 cu in stroker small block. It dyno'd at 467 hp. I specified Iron Eagle 180 Iron Heads. I specified the 180 runners verses the larger sets because of the theory of velocity over volume. I specified the Iron heads because I told the builder that even though I want high power that since this was strictly a street driven car I want to never touch this engine again after I install it in the car. Long term durability that's why I use Iron.