I got a pocket programer ordered and will soon start burning chips.I want to start with the right size injectors so so I dont have to start all over later. I am shooting for 300HP with the combo in my sig. I was thinking that 55pph injectors running at 15-16 psi might be enough. I got about 250HP out of my 40pph injectors at 15psi with my old combo

 

Fastbroker had to run 20psi on his 55lbs/hr injectors to make 300hp.

 

55 pph @ 13 psi

so...

@ 15 psi = 63.4 pph
@ 20 psi = 84.6 pph

that's if the P/V = P/V rule applies to fuel injectors. I've done it this way before and had good results. I was tuning 90 pph injectors @ 17 psi and everything worked out ok.

 

Don't know if this will help, but:
I'm making a little over 300 HP (at the flywheel) with a 350, using 350 truck injectors (55pph?) and 20 PSI (with a custom chip).
Crane Compucam 2030,Turbo City TB and SLP Headers.
-Rich-

 

350 injectors are 62.5 pph @ 13 psi.

So at 20 psi they will flow like a 96 pph injector.

 

new flow capacity = square root of new pressure/old pressure x old flow capacity

So, sqrt of 20/13= 1.24

1.24 x 62.5gph = 77.5gph

 

What would be easier to tune? 55s at 20psi or 65s at a lower psi?

 

Good question, too bad there isn't an answer. Some people like to run higher pressure because of a better atomization under WOT while some people think that too much pressure and the fuel pump won't support as much power. It's best to run TBI injectors in the 10 to 20psi range, either way, so long as the injectors fire the better. I'm a big injector, low fuel pressure guy.
sq.rt of (new fuel pressure / old pressure) times the flow rate of the injectors at the old pressure = new flow rate.

 

Ooops. I thought the P/V = P/V formula worked here. Am I wrong?

...I don't want to be dishing out wrong info. This is how I did mine so I would like to know so I can fix it

 

higher pressure is better it atomizes the fuel more effectively and the fuel pump is only a concern if you are running a stock one and even then i know people running up to 25 psi with one. The only thing increased pressure does other than increase the volume the injector delivers is slightly increase the lag time for injector opening and closing but its a really tiny amount of time and not a concern. There is an adjustment in the prom for it even.