Injector help w/ my P1SC

I ordered my P1SC setup for 24# injectors, most people have told me to go ahead and get 42# injectors and just get a custom chip burnt. After looking into that option I have pretty much decided that at this point right now that sort of setup is a little beyond my pricerange.

I have seen 19# injectors, aftermarket FPR and aftermarket pumps work with 12# of boost on a stock engine with the FMU, The main question i have is What are the advantages of going to a bigger fuel injector if the FMU can compensate for smaller ones? Is there anything wrong with running the 24# injectors on the FMU like the kit is setup for? I only plan of pushing 9 PSI, and I have the fuel pumps and FPR to make them work.... Also has anyone tried to use a boost a pump type device off the ignition? do these work well if you have smaller injectors? reccomended?


any advice much appreciated.

dear Helmsdini :
I have done many testing after many people advices too.
I have all the resources since I have all the tools because I sell them, like a fuel injector testing machine, a 4 gas bench and dyno.
So I decided to give it a try and do all the work.
here is what I learned.
Let me explain to you all the details about the injectors size theory:
1) increasing the fuel pressure to an injector with the use of an FMU has these effects: the injector has to battle to open and close due the increase of fuel pressure , this would lead into: a) lean condition when the injector tried to open at very high pressure ( about 80psi) and b) rich condition when it tries to close because the same high fuel pressure.
These means that the injector "on time" set would not be at the moment it is really needed, maybe 2 or 4 millisecond away from where it supposed to open and close.
2) running bigger injectors cure the problem, because you don't need to run high fuel pressure as you do with smaller size injectors, and the "on time" would not be affected.
But also running bigger injectors have its down effect, this is; a very rich condition at idle and most of the times idle problems.
Also this can be cure in some point with the use of an adjustable fuel pressure regulator, and set it at about 28 psi at idle with the vacuum on, but still you will have a rich condition at idle onto about 2,000 rpm..it depends on the mods of the engine ( cam, intake, heads...)
As you see using bigger injectors does have its pros and cons, but still it is common to all racing fans.
The best thing to do is always to have a CHIP burned into you stock PCM or a programmable engine management engine computer like FAST or ADS or better.
These way you can program you PCM to open and close at a very different points or "maps".
let me give you and example"
I have a stock engine, only roller rockers inside, p600b running 10 psi and 3 core intercooler, edelbrook intake, 73 mm CL flow meter calibrated for 24 injectors, also have 24 pounds injectors, msd 6AL, blaster coil, 75 mm throttle body and egr spacer, equal length headers into cat back and flowmasters, adjustable fuel pressure regulator, inline 255 pounds fuel pump, and procharger FMU.
I have the A9L computer, it the best to do all the mods.
I adjusted the FMU to about 80 psi of fuel pressure to the 10 psi of boost, and I also adjusted the fuel pressure regulator to 30 psi
at idle with the vacuum line on.
I burned a chip so the "on time" of the fuel injector is 3 milliseconds before of the original "map" opens the injector and 4 milliseconds of the original "map" when it close the injector, but only when the engine is at 3,000 rpm and up and the PCM see more than 40% and up of throttle position sensor.
I also played with the advance ignition set of the PCM and retarded 4 degrees of full advance at WOT.
By doing these mods I stayed with a good idle and also I have plenty of fuel at all rpm when its needed.
So as you see it is all a combination of fuel pressure, and injector size, but I have to make clear that running 24 psi injectors it is only good for about 450-500 hp, because the "on time" injection can not be advanced or retarded too much by a simple chip or programmable computer because intake cam timing would not allow the injector to supply enough fuel for higher HP demands.
I also advice you not to go over 450 hp on your stock block, it is a fact that the 5.0 and 4.6 modular engine would not handle more that 450 hp, going over would lead into a blown block, sure you can make 600 hp on a stock block for the street, maybe you can make 1 or 2 passes at 1/4 mile strip, but for sure you would not make 3 passes, no even 1 if you power shift your stang.... this is for sure, so please keep it safe my friend.
I hope this small explanation would help you on your project.
take care and enjoy the boost!!!
Pablo

THanks alot pablo, you shed alot of light on my question. A big concern of mine was to have a well-rounded engine setup. I wanted it to be able to handle the boost on the high end with the injectors, yet also not have many idle issues. I think for now ill stick with the 9lbs of boost and just have a fun street car.


thanks again, Jeremy