Ive always just polished them with a little mothers aluminum polish,works great.I have heard of people getting their alum parts coated, and ive heard sometimes it leaves a yellowish tint behind ,cant say for sure because ive never seen it yellow myself but have read that?
I had my aluminum valve covers ceramic coated. They are an old set of Mickey Thompson covers with the fins and the M/T in the middle and are very hard to polish thoroughly. After polishing one of them about half-way I decided I had enough and decided to have them coated. They look really good, just like polished aluminum. It cost about $60 if I recall.
Well this is for a set of brodix race rites heads, a set of brodix valvecovers and a brodix intake. The surfaces are pretty rough as you know so Im only looking for some stuff to protect the surface from dirt, miscolouring, alu-corrosion. Im not into polishing those parts...
Get some Eagle One Aluminum Wheel Cleaner. It's made for "Non Coated" bare aluminum wheels...it's a light phosphoric acid. Spray it on and hose it off after a couple minutes...it makes the aluminum pieces look brank new. I've used it on intakes, heads etc.