What is the highest fuel pressure that the stock regulator and fuel pump can produce?

 

The question is a non question as long as your talking all stock parts.
First, the regulator is non-adjustable so the pressure remains fixed unless there is a return line restriction or the regulator has an internal problem.
Second, the pump is able to pump at pressures nearly as high as 100 psi but the volume goes down to a very low value.
The two are an inverse relationship, meaning higher pressure is not more fuel flow when large amounts of fuel are required to support more power.
Re-state the reason behind the question so a better/different answer might be possible, meeting what you are after.

 

I want to install smaller injectors with higher pressure which produces a better atomized spray pattern. It will compliment some other mods that will be going along with it.

 

That's an interesting concept.
Some things to know about injection are that the injectors are rated at 39 psi for the specified fuel delivery rating of 19 lbs per hour..
Next, the pulsewidth design is usually to run them between 10% and about 85 to 90% open time so there is a margin at both ends of their range.
Next, metering below about 5% pulsewidths is no longer reliable for idle use.
Next, running them in a power situation at WOT that takes the pulsewidth to 100% open is the limit of fuel flow unless the fuel pressure is raised. Even at that you can only drive them to about the next injector size with increases in fuel pressure before being forced to replace with the next larger size and pulling pressure back down again to prevent over rich conditions at low speeds and idle. The sizes are set so there is the possibility of overlap use in ability to deliver fuel.
Without knowing more about your intent with the hardware, my opinion is that to accomplish the goal, I would try 16 lb per hour injectors and raise the fuel pressure up to arrive back at the same fuel delivery the 19 lb injector would normally deliver.
I have experience with this type action but on a super chargeing application where the fuel pressure is raised by a fuel mangement unit that does this in response to blower outlet pressure rise, forcing the injectors to flow more fuel to meet the additional power of the blower.
For your application, the smaller injectors and an adjustable regulator to raise the fuel pressure should do the trick.
Use injection tables to review this action and set pressure with a gage on the rail to arrive back at the 19 lb delivery rate or the motor will be lean at large throttle openings.
Be awhere that forcing smaller injectors to run at higher pressure will change the fuel delivery curve to a certain degree and max open pulewidths vs high power demands.
The stock fuel pump should be able to handle this application because the pump has a lot of capacity not approched in stock use.
There are single pintal single hole injectors and 4 hole types in 19 lb sizes.
There is one more issue you have to be concerned with and that is the mass air meter output is set to track with 19 lb injectors so it may or may not be an additional tuneing issue in this type application.

 

Thanks for your detailed post!

Some Chevy guys have converted their SBC's injectors to 4.3L Ford units for this very same reason: Higher pressure + Smaller injectors = better fuel atomization. This equates to more power and better mileage.

David Vizard at GoFastNews.com has said that a fuel injector can only compete with a pro-built carb at around 100psi. I'm not going to go that far, but the concept still holds true.

 

I'm getting conflicting information on the actual "stock" injectors in my pickup. Some say 19 lb/hr, others say 21, and still others say 23. Where would I find the most accurate info?

 

Is this a returnless fuel system?

 

HI!... Your "99" 5.4 has a return fuel system and comes stock with 19LB INJECTORS. (ORANGE tops)