[Pampered-Z]

If your looking to go 500+HP then I would go with the 42 injectors if your N/A, with boost or NOS then you might want bigger because you'll need extra fuel. You really want to go no higher then 80% DCs or your holding the injectors open too long and you run the chance or shortening the life of the injectors or having a cylinder(s) go lean.

Note that you are also going to need a fuel pump that can feed those injectors at that HP target. A stock pump is most likely not going to be able to feed 500 HP.

You don't need to be too concerned with fuel pressure itself, more with it staying consistent. That is, it matters less if you 40 or 60 PSI of pressure throughut the RPM range, but that you're pump can feed bigger injectors throughout the RPM range.

Your PF is not going to change based on the pump, if you want to change the pressure then you need an adjustable FP regulator. But the need to change it is somewhat of a mute point. Once your tuned, if you change the pressure the ECM will adjust the injector pulse to compensate, you only need to change the pressure if your using it as a tuning aid. But remember the stock ECM is a bit limited, if you go real high with fuel pressure you could have more trouble getting a quality idle, higher RPMs is less of an issue then better the ECM to control a very short injector pulse for idle and tip in.

The LT1s I've built that are near 400RWHP are geting close to maxing out the stock fuel pump. One at 380RW is close to the limits of the stock injectors, another is just over 400 HP running 42# and the next upgrade will have a new FP on the parts list.

My 383 engine ( blower = extra fuel needs ) made just over 500 RW with 9 lbs of boost and the 42's were getting pushed just to the 80% duty cycle. (racetronic pump and wiring harness) So when the time comes to raise the boost level I'll need larger injectors and probably a second fuel pump as well.