Injector confusion

[lazyxj]

Here is what I'm building
2001 XJ California emissions
4.6 Russ Pottenger short block
Russ Pottenger 0630 P&P, with big valves
CompCam 68-231-4.
Ported late-model intake manifold
62mm TB
Banks header

My build looks very similar to Dino’s 4.6L 268-HP low-buck stroker, which specifies a 24-lb injector.
Problem is, almost every build sheet specifies 24-lb injector, regardless of the horsepower rating, no matter if the projected output is 240 or 268-hp.
Logic would seem to dictate a larger injector for a higher output engine.

According to the injector size formula, on Dino’s site (and many other sites), a 268-HP 4.6 should use 27.9-lb injectors
Injector size (lb/hr) = (horsepower x 0.5)/(no.of cylinders x 0.8)
Let’s say my engine will produce a conservative 260-HP
(260 X .5) (6 X .8) = 27.2-LB
So, should a 27-lb @49psi injector be used or am I missing something?
Are the formulas invalid or do they not take into consideration other aspects to the build? Black magic maybe?

Something like this?
https://fuelinjectorconnection.com/coll ... r-27lb-set

[Cheromaniac]

My build looks very similar to Dino’s 4.6L 268-HP low-buck stroker, which specifies a 24-lb injector.
Problem is, almost every build sheet specifies 24-lb injector, regardless of the horsepower rating, no matter if the projected output is 240 or 268-hp.
Logic would seem to dictate a larger injector for a higher output engine.

I did indeed specify the Ford 24lb injector on more than one build but note that in each case, the fuel pressure (and injector flow) is different for each application. On the Jeep I6 you'll need an injector flow in lb/hr (adjusted for fuel pressure) that's 1/10 of the expected crank HP.
The Ford Racing 24lb injector is rated to flow ~24lb/hr at 39psi. On a 49psi injector rail it'll flow 26.9lb/hr which is exactly what you'd need on an I6 engine in a '96-'04 Jeep that produces ~270hp. The injectors you referred to in the link would also work.

[lazyxj]

Thanks Dino for confirming what I had hoped I understood.
Like so many forums, the core group of knowledgable people is shrinking, as they move onto new interests and hobbies.
Thanks also for continuing to participate in the forum...even if you do own a Ford.

I own a Ford too, used to pull our Jeep around the USA.
https://www.flickr.com/photos/lwade/alb ... 7829693253

[Russ Pottenger]

Thanks Dino for confirming what I had hoped I understood.
Like so many forums, the core group of knowledgable people is shrinking, as they move onto new interests and hobbies.
Thanks also for continuing to participate in the forum...even if you do own a Ford.

I own a Ford too, used to pull our Jeep around the USA.
https://www.flickr.com/photos/lwade/alb ... 7829693253

Total agreement with you Larry.
Dino's continuing participation in the Jeep community is truly appreciated

[Cheromaniac]

Thanks also for continuing to participate in the forum...even if you do own a Ford.

Yeah, but not just any old Ford. It's this one:

http://www.angelfire.com/my/fan/Mustang2006GT/Home.html

Dino's continuing participation in the Jeep community is truly appreciated

Thanks Russ.

[RockyMtn96XJ]

Is there any harm in buying injectors that are "too big" for my build? As in, can I use the 26.9lb injectors in my ~245hp modified poor man recipe?
Just curious, so I know what my options are when buying injectors next week. If I find bigger ones I just want to know If I can use them or if I need to find the "24.x lb" injectors.

If I use larger ones, would I need an adjustable voltage regulator for my MAP to turn the fuel down at high RPM?

[Cheromaniac]

There's no harm in buying bigger injectors than you might really need as long as you have an ECU that can be reprogrammed to reduce the injector duty cycle. Luckily yours is OBD 2 so that makes it possible.

[RockyMtn96XJ]

Thank you for the info.

[RockyMtn96XJ]

I need a reminder now...

In my (late build) '96... no fuel rail regulator.... would I need the DIY MAP voltage regulator for my injectors? I dont want to mess with tuning the ECU if i dont have to. Are there any other "quirks" I should remember about with the fuel pressure and all that?

But..... I think I saw the voltage regulator is only needed up to 1995, or for models with the regulator on the fuel rail (including early build 1996 models).

Or will the ECU auto adjust for fuel/air in my case? (OBD2 and fuel tank regulator, larger injectors, a lot more air flow)

Facts: poor man stroker, typical cam swap, opened intake and exhaust ports on head, and air intake about 1.5" deep (port matching) but header left alone) , big throttle body with opened intake.... the usual stuff. Just wondering if I need to do anything I have forgotten about regarding fuel since its been a DANG year since I started this project.

I can give the info on the injectors I bought if needed. I'll have to get home and look at what I bought because I forgot, but I know they should be correct for my build. I highly doubt I purchased injectors that were slightly under the calculated requirement. I'm sure I bought the size that is just above the calculated requirement.

Thanks for the reminders.

I'll start a new thread in the project section once I'm done and can spend time posting pictures and useful info on my stroker build.

[mpgMike]

Here is my experience with my '95 ZJ (no fuel rail pressure regulator) with a 4.6 stroker:

Stock injectors ran just fine. Wanted to "upgrade" to the Ford 12-hole. Stock flows (I think) 21 lbs/hr, while the Fords flow 24. (Even if the numbers are wrong, the relationship is right.)

It would run rich on cold start until the O2 sensor warmed up, then within seconds lean back to normal. The more I drove it, the better the stock PCM seemed to work with the larger injectors. Had one die, replaced it. Had another one die and..

"Upgrade" to GM EcoTech 2.4 FlexFuel E-85 compatible 12-hole injectors -- which flow at 27 lbs/hr. So at this point, I've gone from 21 to 24 to 27. It took much longer for the stock PCM to adjust, but it now starts and drives just fine.

Note: I have been toggling back and forth between the stock PCM and rusEFI UAEFI stand-alone. I've mostly used the stand-alone for ignition control, as I have 6 individual GM LS coils for it. I swapped the NB O2 for a Bosch 4.9 LSU and took control of the fuel. That lasted about 1 tuning session before I lost injector #4 driver. Put it back to stock control. I'm putting together a replacement, but with flyback diodes on the injector drivers.