I've used Simple Green to clean aluminum parts that had greasy hand prints and dust and dirt. But it was still fairly new (a few months old). Cleaned it right up and made it look fresh out of the box. But as far as anything real old, I would suggest maybe media blasting?
Lemon pledge. Give it a good soaking then let it air dry for a few hours. Wipe it down. You'll have to repeat the process about once a year, but it will keep your intake in a condition that a quick rinse once in a while will keep it looking like new.
Jet-Hot coating. You can polish any fuel stains off and most will wipe off if you get to them quick enough.
I use MAC's aluminum cleaner from NAPA. It's basically Phosphoric acid that re-etches the aluminum. Looks brand new when done.
When I restored a set of aluminum valve covers, I media blasted them first and then coated them with fresh/new engine oil and let it soak in before wiping it off. Later, if it got dirty oil of them, it wouldn't soak in a leave a stain, it would wipe off. They looked great, looking new for several years until I sold the car. Sounds strange, but it worked better than any other method I've tried.
I had mine ceramic coated dull silver...looks just like brand new cast aluminum, and has been looking that way for 2 years and lots of driving. Fuel and other stains wipe off easily.
Media blast , then use Eastwoods Aluma Blast. This is the closest color I have found to keeping it look like it was never fooled with. Simple Green when it gets dirty.
If you want to keep the raw cast aluminum look it will as you know be vulnerable to stains from a variety of things. A solution as mentioned is to have it powder coated, Eastwood sells a cast aluminum looking powdercoat. If the raw aluminum is what you prefer to keep, look up a product called Aluminum Jelly. It's a cleaner that will best keep your manifold looking new. Edit : By the way if you use any form of mechanical cleaning method like the next poster suggests - wire brush, say goodbye to the untouched raw aluminum look. You may as well have it powder coated in color. And I can't believe someone actually suggests WD40 as a cleaner
as said, a good cleaning with an abrasive, I like WD40...with steel wool...seems to help sealing it as well...the PO had painted mine so I cleaned it up as good as I could and hit it with cast paint...media blasting would be the ticket to really clean out the pours though...
Try Meguiar's Hot Rims aluminum wheel cleaner. Spray it on, rinse it off with water. Remove a lot of gas stains.
Painting with Aluma blast works just fine, I do all the underhood aluminum with it alternator etc. I do not do valve covers and air cleaners however.
I used "Etching Mag Cleaner" - It works great! Labeled - Not recomended for painted or polished wheels! AVAILABLE? I haven't seen it in the store lately...maybe they discontinued it...? I have a stash at home though! SOON: To do it again (I'll be doing it shortly when the intake is out) I plan on removing all the stuff, injectors, sensors, hoses etc. .....It is etching! Aloha Tommy
Same thing as Eslpe T, I use eagle one mag and aluminum cleaner. Spray it on, rinse it off, easy! The only problem is then you have to clean the rest of the engine compartment.
a good cleaning, and a clear coat.........I have also painted silver and clear coated, made cleaning it later alot easier. Dirt and stains seem to not stick to the coated surface. Don't clean the clear coat with an agressive abrasive or it will scratch.......