Im running 750's on my Scoob and producing 380bhp (not sure on the duty cycle but at 3bar) but I used to run 550's on my GTiR and was producing 400bhp (4 bar fuel pressure). I would say it is always better to get slightly bigger than you require but they are just fine.
So if I want 350hp and run 1.4bar boost then I'll need near on 600cc injectors. I suppose the more boost I run the more the fuel pressure will be so this figure drops...
I may get some 550cc injectors then; like you say mate they should be fine
[FONT="]Injector Sizes and BHP limits[/FONT]
[FONT="]Remember that the stock fuel pressur regulator will raise fuel pressure in a 1:1 ratio with the boost. For every psi of boost above ambient pressure the FPR will add 1 psi of fuel pressure.
If you are running 14psi of boost, your fuel pressure at WOT (wide open throttle) will be 43.5 + 14psi = 57.5psi. This is why you should not raise your base WOT fuel pressure above 4 bar. @ 4bar base fuel pressure and 14psi you will be running 58psi + 14psi = 72psi of fuel pressure @ WOT. This is why its important to find the right sized injector. I garuntee any stock rubber hose will be a bit stressed at this pressure and your fuel pump will be hard pressed to keep that pressure. Also your injectors may stick because the valve cant over come that high a fuel pressure.
You would have to adjust the fuel pressure regulator to supply less fuel than standard then, so that the amount of fuel served by the injectors is the same as with the 444cc ones.
If you are going to increase injector size, you _have_ to tell the ECU that the injectors are bigger, or it will overfuel.
The amount of time the injectors are open will be the same, but as the 555cc injectors flow more fuel, thus leading to the overfuelling.
...and while we´re at it - I need bigger injectors. Running 600cc injectors at 4 bar, but I´d like to lower the fuel pressure to 3 bar. Anyone have real life experience here? It´s for my 3071´d Pulsar at... let´s say 1.9 bar for argument´s sake. Looks like the 700cc SARD option is discontinued, so perhaps the 800 ones?