Well ya know everyone calls it a boat anchor because its a cast block. So I figured lets see just what a bare block weighs. I bet it cant be 200lb. Aluminum weighs aprox 36 percent the weight of steel. As far as cast aluminum compared to cast iron Im not sure on actual weights. Still figuring on that X.36. If the block did weigh all of 200lb an aluminum block would weigh 72lb which would be a savings of 128 lb. I believe aluminum casting are built heavier though so that would make the aluminum casting heavier.
128lb would be a decent savings and justify the critisizm GM gets for still using some iron castings. However if the block only weighs 150 you only save 98lb maybe but we know an aluminum bolck would need reinforcement that an iron does not.
I have built some of my stuff out of aluminum over the years. A full aluminum box for my old 81 Toyota 4X4. Complete with pockets, even in tailgate and removable side racks. It was very light and is now on a trailer frame (that gets little use).
Also the belly pan on my log skidder is heavily reinforced 3/8 with some 1/2" aluminum. It need to be two pieces and I needed something I could hold up there myself and get the bolts started so Its aluminum w/countersunk bolt heads. Very much a work of art. Aluminum panels on my log trunk bed, a few other odds and ends.
So Im not anti aluminum but I know its benefits and its short comings. On something as big as a PU box where using 1/8 steel sheet would give you a loaded truck before you started compared to 1/8 aluminum. But Im not so sure a cast bare block is all that heavy. I loaded my straight 6 diesel block myself into the back of that Toyota in fact with no problem.
Aluminum is or at least was 3X the cost of steel. !/3rd the weight 3X the money.
86 LeSabre coupe, 90 Regency, 90 Ciera Cruiser and the 97 LSS have a new stable mate............06 G6 GTP coupe, white with taupe & black interior