9-10 boost psi on stock injectors will work for a short while. However with the stock 420A fuel pressure you should be at 50-55psi with no boost. When you boost on stock injectors you will see 100+ FP to compensate. Now on stock 235cc injectors, 100psi is a lot of pressure. Some have good luck with them, others crap out. It all depends on how good the injectors are and if such small injectors can take the added abuse. Keep in mind everyone that not all fuel mods for the 4G63 will work with the 420A (ie resistor pack) It all depends on the car. The most "standard" mechanical tuning for a setup like this (meaning most 2gnt'ers are running a stage 2 setup) would be to use 30lb/330cc injectors and with an SFMU lower your idle fuel pressure to 22psi. When you hit boost you would be right at 45-55 psi on fuel pressure. This setup has worked out a lot for people due to the ECU thinking while the car is under boost, it is still reading the base fuel pressure of 50-55 and not correcting by having you run ridiculously rich or going into fuel cut due to running lean.