I understand that.
I found a good link (after closer inspection):
http://www.delta-tcompany.com/nozzles/sizes.php
Of course I'll have to convert SCFM to gpm/gph! I'm still not fond of the straight section in that nozzle, so it's gonna have to go.
I just got a call back from a rep from TechRep. He's going to fax me some numbers. He says that the calculation of a restriction of a nozzle is similar to that of an orifice plate, but with a factor added.
We'll see!
[edit] the link above has a chart for air, not water [/edit]