Talk about engine building here. New products, tricky questions or showcase your work - If it's engine building related it's welcome here.
Hey is there any modification I can do to the jz oil pump to improve oil flow?
I haven't had much to do with the 1 JZ personally but it appears the 2JZ oil pump is used as an upgrade. In terms of the 2JZ oil pump there's not too much concern unless you're considering massive rpm. If you want to do any improvements then you can focus on rounding any sharp edges in the oil pump passages to help flow.
This may be completely wrong - it is not my sort of engine, but it would seem that the 1JZ used a sintered gear on the crankshaft that fails - seems that this is a problem on any engine with a sintered gear and something to replace ASAP with a steel one on any engine. The 2JZ is apparently steel and why it is strongly recommended - it also seems that Titan make the most popular aftermarket pump* with the modifications already done - http://www.titanmotorsports.com/2jz-modified-oil-pump.html. There are also aftermarket billet oil pump drive gears available, but they just seem to be for the 2JZ and I don't know about their fitment or need regarding the 1JZ.
*Might be a little pricey, but it is a new pump with the work correctly (I trust, they've been doing them long enough) done ready for fitment - and considering the cost of a ****ed up oil supply, I figure it is cheap insurance. If you do go that route, you could also ask them about pump drive gears.