Thanks all for your advices.
The damage on the engine finish looks like as if the oven cleaner fluid has etched the aluminum. No paint was peeling off at all. Even sanding the spot off didn't help at all but only made them look unaturally brighter and shiny compared to other surface area.
Here are the sample photos what I want my engine to look like.
http://www.boomplustoys.net/images/J...e_Manifold.jpg
http://www.prostreetonline.com/pso/p...ox/bloxim3.jpg
http://mlbz521.scorchgaming.com/Prel...ntakeafter.jpg
http://www.civictyper.ca/Civic/K20A%...20Manifold.jpg
http://www.clubcivic.com/board/showthread.php?t=108068
The last link shows good contrast between the new and the old. Mine has more ugly dark silverish looks on many different spots though. I'm not an expert on the aluminum finish but from what I've seen, the aluminum doesn't look like it's powder coated at all. No paint was peeling from mine when scratched. As you can see from the links, the silverly color looks almost bare natural, but also it looks too even to be bare. There must be some kind of electroplating treatment the factories must do to make them look clean and nice. I prefer the factory look than polishing ones.