Keep seeing this in Diesel Mags and was curious about it.
EDM is where they electrically enlarge the nozzle (not sure of the specifics). EH is where they force a fine abrasive paste through the holes to enlarge them.
From my experience EDM make more power with less smoke than a similar flowing EH nozzle. I started out with .0085" EH nozzles on my 530's and was running SLOWER than i was with hybrid inejctors (.010 EDM), stock hpop and a smaller turbo
. I picked up over 50rwhp just by switching to .012 EDMd nozzles from the .0085 EH. Yes i know the EDM are bigger, but they flow very similar to the .0085 EHd nozzles. Ive been told EDM tend to have a rougher hole finish and i think this helps the fuel atomize better resulting in more power and less smoke