[amerdunbar]

Just bead blasting will give a rough, silvery look to it that will corrode and stain really quickly if left as is. I haven't worked on aluminum car engines enough to know what's on yours, but my guess is the block has some type of anodize seal to protect it. The intake manifold, on the other hand, is probably silver powder coated. Are you just trying to fix the finish on the intake manifold? What type of finish do you want? Did you just dull it, or has it started peeling?