CorvetteRules

Prior to spring I'd like to clean up the valve covers and plenum cover on my 91. What grit sandpaper have you found to be best to use? And once prepped what protective coating would be best?

65Z01

There's another thread on cleaning Al parts that may be helpful.

Kmcoldcars

The answer depends on the condition of the parts to be sanded and how smooth you want them to be when finished and what coating you will use. If the parts are very smooth I would start with 1000 and water. If that takes too long to remove defects I would go to 600 or 400. If they do not work try 220. Then after you have removed the defects start wet sanding with finer sandpaper. If you want the parts to be clear coated and shine well finish with 1000 , 1500 and then 3000 sandpaper. Then buff.
If you clear with a thicker opaque coating 600 and water is probably fine enough.
The choice of coatings cannot be answered until we know what you want on the parts - clear, opaque, thin, thick, etc.

Kevova

Plenum is aluminum. The valve covers are probably magnesium. Sand or bead blasting to remove old coatings. The valve covers may take some work to get them smoothed out to paint. Might try YouTube to get an idea what's involved.