i just finished installing my harwood 4" fiberglass cowl induction scoop on my factory metal hood and was wondering what grit dry sandpaper should i use to sand the scoop and the hood before priming? the hood has the original factory paint(1973 chevelle)and the scoop has the gelcoat primer.i know to wipe them down with paint prep wax and grease remover before sanding.does the type of primer i use dictate what grit paper to use? also would it be okay to use a pneumatic jitterbug sander to sand the metal hood to bare metal and maybe sand the fiberglass scoop by hand? thanks for your advice.by the way,i know the fiberglass scoop/metal hood combo isnt a good practice but my budget wouldnt allow other options.

Remove ALL the old (original) Paint. You didn't say if the scoop was moulded in with fibreglass and filler yet. You can use as coarse as 80 grit on the metal surfaces, to strip, switching to 180 prior to prime. 240 is probably the best grit for the gel coat. For the areas with chemical filler use 180 prior to prime. Remember the coarser the grit the deeper the scratch that the primer has to fill. A DA (orbital) sander is fine. Keep it flat, and speeds low, so as not to gouge out gel/fillers, or overheat metal. Block sand primer with 240, maybe even 180, depending on how good you body work is, reprime, final sand 320 or 400 depending on paint product.
Karl

thanks,man!i haven't filled in and shaped around the hood scoop yet.the paint store sold me some Dyna-Glass fiberglass filler to smooth out the transition between hood and scoop.i also bought some USC AUTOBODY ICING polyester finishing putty to do the fine finishing and fill in scratches.the scoop is the style with the flat flange around it that mounts underneath the hood up through the opening i had to carve out.cutting out the webbing and cutting the hole was tedious work but it looks real good.i used the 3M AUTOMIX panel bonding adhesive to glue the scoop on.its good stuff! i just hope it holds. ;)