Ariel increased the bore of the feed piston around 1950 (based on the part number). I had an early small bore one (0.186" dia piston) reconditioned by Drags and it came back at 0.267" (They sent me a reconditioned later body not the 1936 body I sent them ). Working out the surface areas of the two (0.027" and 0.056") that's just over a 50% increase in piston surface area. So in theory (stroke was unaltered) that should give a 50% increase in pump output per stroke. (The recon return piston was only slightly bigger (20 thou) and was therefore still 2x the surface area of the feed at 0.120").
Looks like Drags don't do exchange recon pumps anymore, they do their Hawker brand which is listed as 50% increase flow rate over standard. They list it under the older pumps part number (2212-29). So I wonder if that 50% more flow than standard relates to the old small bore pump or the later large bore pump? If its 50% more than the large bore then that's a lot of oil flow !!
I will give them a ring next week to see.