There is a lot of misconception that you need rotary tools or special "compounds" to polish your plenum. It can actually be done with a few dollars.
- 3M Sandpaper.
80, 120, 220, 320, 400, 600, 800, 1500 grit
- 3M marine aluminum restorer (found at Advanced Auto/parts america)
- Mothers Aluminum Polish
- Polishing cloth
Start by removing the plenum off of the car. If you look at the plenum you will notice you will have to sand the plenum separately in some areas due to the design. (You will know what I mean once you start. )
You will also see the plenum has a "cast" type finish. This is what has to be removed. Take the 80 grit and start to sand the length of the plenum. .
You may want to use a small wood block to assist you in achieving a smooth sand. While you are sanding, make sure you view the plenum under different lights and angles to be sure you are removing ALL of the "cast". When the plenum looks smooth with no cast, move on to the 120 grit sand paper. Sand with the 120, then move on to 220…..320. When you get to 400, this is the most critical. 400 is actually the last stage you will work at that can "remove" scratches. Sand with 400 for 30 minutes or so. Do not cut corners in this stage. After you’re sure you’ve spent enough time, apply the 3M aluminum restorer on the the plenum. Buff it out with a separate cloth. This is a test buff. The shine should be dull with no scratches. If you see scratches, go back to 400. If it looks smooth, move up to 600. Again, take your time with 600 . Then move on to the 800, then on to 1500. Now buff out again with the 3M marine restorer.
Now, after you have buffed out with the 3m, wetsand with the 1500 grit. This is what gives you the "mirror" type finish. You may want to use some WD-40 to make certain the surface is lubricated. I cannot stress enough how wet you need the plenum to be.
After you have wetsanded with 1500, buff out again with 3M restorer. Follow with MOTHERS aluminum polish and you should have a "mirror" professional looking shine.
DO NOT use mothers or any other type of "aluminum" polish once the plenum has been high polished. Simply use Windex and streak with paper towels. Rubbing compound, Mothers, Blue Magic, and any other "aluminum" polish will leave fine scratches that will dull the shine.
It may take you a few trys to get this job done right. But it certainly can be done by anyone who has the patience. It took me 3 trys , and about 4 days to get it right.