Clean Turbo Cover

With a polishing pad on a drill I used

Wenol and it did a pretty good job of cleaning it up. Used it on the uppipe too and it actually shined up.
Give it a try.
Are you trying to polish the housing to a mirror like finish? If so start with 80 grit and move up to 1000 grit. You can use a 90 degree grinder with a sanding "cookie" on it and a flapper wheel works good also. It takes a while to get the tight spots but can be done.