You got my gears turning, John! The weight differences you describe between the cast and the forged pistons may be as you say. I however, believe that an aluminum forged piston is denser than a cast piston due to the fact that it is pounded/beat into its rough shape and then machined to final dimensions. Denser material equates to more weight. During the forging process, the materials' molecules align themselves more uniformly than if the same material were poured into a mold and cooled. As I said before, stress is induced into a part whenever it is machined. Stress is also relieved as a part is machined. This all depends upon the machining operation and part geometry. It should also be noted (again) that a good quality set of aftermarket slugs are gonna be very close to each other with respect to their weights. It doesn't matter if they are cast or forged, manufacturers have designed (into the piston) areas where material may be removed for the sole purpose of matching the weights on a set of pistons. The way I see it, there must've been valid reasoning behind AMC engineers' decisions to use forged cranks, rods, pistons, etc in their engine designs. Most likely for the same reason their blocks have high nickel content; it's all about durability. My belief is that one shouldn't skimp when it comes to reciprocating parts in any high output engine. The piston/rod assembly materials are subject to both tension and compression. Cast parts are good (depending on application) to a point and for many of the reasons you stated. Ideally, I would prefer to have all of my stuff manufactured by the sintering process. You have the best of both worlds and no stress in the part when it's made this way. Bob Rapp NN, VA 70 Machine