[rbohm]

aluminum bloxk are more reliable than iron blocks are, especially with aluminum heads. you have far fewer head gasket problems when the heads and block are the same material. also aluminum blocks use STEEL sleeves in the bores. if you want some real fun, get ford to set you up with a plastic block and head they were experimenting with in the 80's. they actually used it in a race car, the mustang probe, and it did ok. the block, head, oil pan,etc were all plastin. the only metal it used were steel sleeves, bearings(cank and cam), valve guides pistons, rods, valves, and cam. the engine made like 650hp from 2.3 liters.