i have been sanding my plenum for over an hour now and it didn't change that much. it is a lot smoother and a little bit shinnier, but not even close to done. is this how usually long it takes?

 

now which is it? sanding or polishing? Sanding is just that, sanding. If you have smoothed the plenum to your satisfaction, then begins the polishing, using compound and a buff wheel mounted on a bench grinder, drill, dremel. Starting with the course compound you polish the plenum, going with finer compounds (and clean buff wheel), til its mirror shiny. Check out this thread for good info and links. cheers, Bob

https://www.thirdgen.org/techbb2/sho...hreadid=103187