i assume you have some sort of aftermarket ecu jobby?

if so it depends on how your ecu is setup, and how much fuel its giving it, and how much fuel pressure it expects.

if you are able to aquire a ecu map and you should be able to figure out/be told what fuel pressure it is designed for.

worst come to worse...start high (50psi or something) and just keep dropping it till it runs good enough to get it to where you need to.

btw stocko 4age spec in the manual sais 35psi or so. so thats a good place to start. but yer if your running an aftermarket ecu its not really much use if its setup differently.