RE: Exhaust tips
Castrol Superclean is actually a very good cleaning product for removing this type of crud... HOWEVER.... it is quite noxious and will probably remove the flat black paint inside the tips along with the crud. Based on my experiences with the product I would not use it in this application for that reason. Be aware... if you do use it you may have to repaint the inside of the tips after a few applications.
Individual results may vary...