[ This message was edited by: scratch on 2007-01-26 13:52 ]I learned this simple method from Lang Hindle (Hindle Exhaust) a few years ago. I tried it after a marathon dyno session (100 pulls!) on my R1. The pipe turned all kinds of crazy colors, and was put through more heat than we will ever see. I just cleaned my S3 this morning, after a 4 hour dyno session in a 100 degree dyno room the other day, and you can see how nice it turned out.
Will it make it look "brand new"? Of course it won't...nothing looks brand new unless it is, well, brand new.
It will however, make it look better than anything else will. The very top of your header pipes will be the toughest, and not all of the discoloration will go away because there is a lot of debris, chemicals, fluids, etc that have burned into the surface.
The secret formula...TOILET BOWL CLEANER! The key ingredient is Hydrochloric Acid. Personally, I use Lime Away.
First, you need to thoroughly clean the pipes as good as you can.
Now, put on your rubber gloves. You do not want this stuff eating into your skin.
You do not have to take your pipes off, but it's definitely the safest and most thorough.
Put some Lime Away in a bowl (full strength) and get yourself a very small brush...you want a small one so you can fit it into tight areas without getting it all over everything.
First do a test in a conspicuous area of the pipe. Wipe a little onto the pipe, sit back a few seconds, and watch the discoloration disappear like magic!
Now GENTLY rinse the stuff off so you can see how clean it is. Don't just spray the hose all over because you risk getting Hydrochloric Acid all over your painted surfaces...which is bad.
Now that you're comfortable with what it does, start doing small sections of the pipe at a time, then rinse, then go onto the next section. For the top of the header pipes, I took a plastic trash bag and put it in between the pipes/engine, and pipes/coolers to protect them from splash. In the stubborn areas, you might need to hit it twice to clean it up.
If you have a brushed stainless steel section of exhaust (midpipe backwards) that looks really bad, you can clean the color with this method, and then hit it with Scotchbrite. DO NOT use the scotch brite on the shiny chrome!
It won't stay bright forever, as it's simply not possible. It will however clean it up very nicely, and you can just re-do the 10-minute process every now and then to maintain it.