[mrrec]

The GM engineer has some good info and I believe a good deal of it applies.

I own a small mfg co and have experience with new alum castings. Not all castings are media blasted, though, after shakeout (removal from the mold) and I don't know what they did in the musclecar era on trans parts and intakes. You can bet there is not one right answer!

Sand castings (intakes, trans main cases) are very bright (almost aluminum paint bright) as cast in many cases. You can duplicate this with an older casting (regardless if it has been blasted before) with a "brite dip" in acid. There are several formulations including 94% Phosphoric acid, 6% Nitric acid. I glass bead first, then dip. Contact time of the acid determines brightness. It works.

Die cast aluminum cannot have the original finish (skin) restored by media blasting. As cast, diecast has a much darker, smoother look. Once you blast it (vibratory, tumbling, media blasting), you're done. I have not found any procedure to accurately replicate this finish (just find a tailshaft housing someone hasn't messed with!).

The "reskinning" thing is a misnomer. You really can't "reskin" (and like the GM engineer said, sand cast aluminum doesn't have a skin anyway). I had McNeish do an intake to see what he was doing and it is appears to be just a media blast (media unkown). I've done the same with glass beads. It does look nice, though.

Cast iron "reskining" by those saying they do that is probably ceramic coating. Sand cast cast iron does have a bit of a darker colored "skin" in some cases. I had a set of exh manifolds for my Z16 ceramic coated in grey, then painted them Chev orange as proper. Hopefully, as the orange burns off over most of the body, they'll reveal the grey and stay that way.

Dave