Originally Posted by
ogitrev
Dont be foolish and get more injector than you need. And if you dont know why, ask yourself why high horse power cars, and sport bikes run dual sets of injectors. Hint: has to do with pintle inertia!
..which really dictates the minimum on-time and low pulsewidth linearity of the injector. Minimum on-time is somewhere around 1.0mS on the 740's sidefeeds. It seems to be pretty linear in the low end of the scale as well. I never had a problem idling my car on 740's with reliable/repeatable fueling at 1.2mS at 900rpms. Mazworx has a sweet plot of Bosch 1600's that go way non-linear around 1.5mS, if you want to see some ugliness.
Bottom line is, if you're going to see over 350whp frequently, you need more than 550's on standard fuel pressure. So your best options are 740's (see above) or running 550's on 4 bar of fuel pressure.