S13 Vs. S14 SR20det Waterpumps, why the change?

[Rezlo]

Im running a S13 bottom end with a S14 head with quite a few things done, when I did the combo (cracked sleeve on the s14 block) I noticed a large difference between the S13 and S14 pumps,

Both are completely swapable but the S14 pump has a cavity that seems to let it circulate less water, after swapping my neer new S14 pump out and putting the old S13 pump in I noticed a HUGE difference of about 20 degrees outlet temprature drop when cruizing at 4500rpm + along the highways and also around town it was a lot cooler.

Problem? my S13 pump desided to leak, now that ive thrown the S14 pump back in im right back to where I started with a mild overheating situation when im sending it along the highway. Im not sure if its my stock oil to water cooler (engine oil cooler) my S14 has stock that makes it raize the temps up more but it seems a bit odd that nissan would take a step back in the performance of the water pump in the later years.

My only problem now is that I can find a S13 SR20 pump here in africa, anyone know if any of the SR20DE's came with a similar pump? Ive seen a pic of a KA pump of a pick up truck here in SA, it also looks a little similar? can anyone confirm if there is a simple swap so I dont have to wait for one from the US or JP which takes like 6 weeks?

Ive also heard alot about an aftermarket S13 pump thats alot more effective, anyone have any info on this? ive searched but found nothing,,,