Acid dipping is not sufficient prepping for any coating.
Acid is only for loosening the coating that needs to be removed, most of it will come off but not all of it, this is where sandblasting comes in, it is the best way to clean and prep a surface for paint/powder coat at the same time. Most powder coat plants will then put the parts through a cleaning process to remove any grease/deposits before they coat, cheap ass places will just coat them though which is where you end up with bits in the finish/crazing/oil spots etc.
Sand blasting is THE best finish to have on any metal part before it is powder coated, it sticks to this like s hit to a blanket 
 
 
Be careful who you give your cast ally parts to, if they go into acid (proper stripping acid) there is a good chance they will deform/soak it up and they will be scrap, ive had it happen with my stuff in the past.
If you want the standard bare ally finish then have a look at the parts diddler got soda blasted in his thread, it doesnt get much better IMO 
 
 
When I did my alpina inlet I sandblasted it and painted it satin black, I wouldnt want it powder coated TBH, it fills the detail and looks a bit gash