Try some of your wheel cleaner on your exhaust tips before going at them with your polish. I maintain my supra's stainless tips well, but the car runs rich...and they build up with carbon in just a few days. I was cleaning my wheels and walking around the back of the car with my raceglaze wheel brus hand AG CWC and saw the tips. thought "what the hell" and applied the CWC and aggitated quickly. when I rinsed the next wheel, I did the same to the exhaust and it left a nice shine. no more getting my MF's needlessly dirty
Any APC will clean the exhaust pipes nicely, APC + 0000 steel wool is epic win for keeping them super shiny, I do it for every wash.
^ yeh exactly ive had titanium burnt tips on previous cars, and soon on the GTR, and ive used regular car wash soap to maintain them (cant use metal polishes) the trick is to give them a wash each time to prevent the carbon building up - i do it while im going around the car soaping the under panels
I learned that tip a while ago by JL. He uses Megs WB on them and they come out great. Check out the 3 series I just posted..you'll see it did it there although unfortunately I didn't get a close up pic of them at the end. It cuts the work considerably.