If we assume the stock 4-14#/hr injectors, a fairly safe 80% injector rate and the .6 BSFC listed above....you get a max output of 74.67hp. Wow, how does Ford ever make these trucks run?
There's something funky with that math . . .
Here's the formula I'm familiar with:
InjectorSize = (HorsePower * BSFC) / (#Injectors * DutyCycle)
BSFC should be around .55, and I wouldn't go higher than an 80% duty cycle. With this formula, I come out needing 19 pound / hour injectors for my 130 horse engine. Honestly though, I've never seen anywhere NEAR an 80% duty cycle on any of the datalogs I've done while tuning. (With my foot REALLY into the throttle while racing uphill, my injectors are humming along at 60% or so, and it's not running lean, either!) On one hand, that demonstrates how gentle I am with my truck--which, if it sees 4 000 rpm means that someone ELSE is driving--and on the other, how the math enables us to properly size injectors before we ever drive the machine!
Of course, all of this depends on fuel pressure, too. Once we boost an engine that has a rising rate regulator (like the factory fuel pressure regulator on my truck), one psi of boost = 1 psi of additional fuel pressure. This is why George is able to run 15 or so psi in his machine using the same injectors I'm using at 5 psi.
Also, weren't the stock injectors 15 pounds / hour?
It's easier to tune for a good idle with small injectors because there is more room to play with pulse widths when the need for fuel is small. The engineers at Ford are WAY smarter than I am. Since I've begun this journey into the realm of abnormal aspiration, I've developed healthy respect for those guys!