Learn me: Injector differences and hole count

I have a few issues with my truck right now.  I'm going to be digging into the head again, one of the things I didn't do during my engine rebuild was replace the injectors.  Truck has 360k+ on it right now, so I figured I should look into it.

My brief start of research, combined with this article https://grassrootsmotorsports.com/articles/can-retrofitting-newer-injectors-really-provide-qu/ shows me that I'm not really up on what the differences in injectors are.

For my truck, The stock injectors are rated for 14 lbs/hr @ 39 PSI.  At the 58 PSI pressure of a 300 they put out 14 * (58/39)^0.5 = 17.1#

Are all injectors rated at a normal 39PSI?  Do I look for 58PSI rated ones?  I seem to remember reading somewhere that the late model 5.4L Ford injectors have a multi-hole design for better fuel atomization, but I haven't verified that or their flow rate.  Is there a general database somewhere with the which injectors are the best for a given flow rate?

Is there any substantial difference in the fat bodied injectors and the skinny ones?  Do I need to worry about impedance or anything other than making sure they are 12V?

'93 F150, 4.9L, Auto

Related topic.... not sure if they'll work in your 4.9L, but I have a spare set of reman injectors from my Ford 4.0L.  Never installed.  I think they're 18lb/hr.  Maroon tops.

UREMCO 9316 is the application, reman in the US.  I could sell them to you if they work.

I think I'd need to do some upgrades for those to not be spraying too much.  19lb injectors are a semi-common swap when you start building HP, but that requires messing with the regulator and a couple other things I think.

1993... maybe.

You have quite a bit of flexibility.  I believe 27% is the magic number.  Once the ECM has gone 27% richer or leaner to keep stoich at the O2 sensor, it will throw a code.  It goes "off the map."  Otherwise, it will run a little rough for a few miles until it learns.

I double checked... looks like yours were 15 lb from the factory (but could be rated at a different PSI) and mine were 16 lb.  But the same exact engine in the Aerostar had 21 lb injectors (probably with different tuning or fuel pressure).

But, I understand the desire to not go nuts on altering things.  Just know that you can hit a pretty wide range and be ok.

Anyone else want to chime in with anything?

So the era of your truck- you likely have some very simple, basic pintle style nozzle.  I'd doubt there are any holes or angles or anything special on your truck.  It's going to have pretty basic emissions requirement, so no expense for high end injectors.

You *can* get better injectors, but they are not likely going to make much difference.  It will help some with cold engine vaporization, so if you have any hesitations on your old injectors, it could get better.  

Not sure why you are asking about 58psi.  Your truck should be running 39, as that was common in the era for PFI.  The higher PFI injection pressure came along with returnless systems.  

IMHO, KISS- just send your injectors off to be cleaned and blue printed.  

alfadriver (Forum Supporter) said:

Not sure why you are asking about 58psi.  Your truck should be running 39

Exhaust manifold immediately adjacent to the intake.  Ford went through a bunch of tries at fixing it, ducted fans and heat shields and such.  Ultimately they upped the pressure to prevent boiling.  It runs at 58PSI or so

In reply to Mr_Asa :

Forgot about that.  Still, the injectors are rated at 39 as that's what they ran at for most cars.  Even though you run higher pressure, they were sized via 39psi flow.

Industry standard for flow rating is 43.5psi 3bar