Do I need 24# Injectors with these mods? - opinions please!!

I think you should be fine with the 19lb injectors. Mabe just look into a fuel pressure regulator and add a bit more to help out.

There should be some sort of calculation that can come close to telling us around what WHP that our injectors will be in a heavy duty cycle.

SWYZ721 said:

There should be some sort of calculation that can come close to telling us around what WHP that our injectors will be in a heavy duty cycle.

Click to expand...

Fuel Injectors:



Just as the wrong sized jets in a carb can cause decreased performance and driveability problems, so can incorrectly sized injectors. The following calculation can be used for approximating fuel flow per injector based on horsepower (HP) and Brake Specific Fuel Consumption (BSFC).

Note:

1) Engine HP must be a realistic estimate.

2) BSFC is determined from engine dyno measurements. It typically ranges from 0.4-0.6 for gasoline engines. A BSFC of 0.5 is a safe, initial estimate.


BSFC =
Pounds of fuel per hour

--------------------------
Brake Horse Power




3) The 0.8 multiplier for the "Number of Injectors" helps derive a practical "Max Injector Flow Rate" for each injector based on an effective real world injector operating pulse time and fuel flow. It is unrealistic to establish the fuel flow to an engine based on an injector operating pulse time of 100% (wide open all the time). This calculation uses an injector operating cycle of 80%. Some full race engine management systems may operate at 85-95% duty cycle, but extended operation may eventually overheat the injectors and cause irregular flow rates and poor low rpm operation.

Injector Flow Rate (lbs/hr) =
HP * BSFC

---------------------------
number of injectors * 0.8



With a known injector fuel flow rate you can get a rough estimate of the systems capacity by using:

HP =
IFR * number of injectors * 0.8

---------------------------------
BSFC


where
IFR = Injector Flow Rate (lbs/hr)


Increasing the fuel pressure can often provide increased fuel flow and better atomization. If you know an injector's static (non-pulsed) fuel flow at one system pressure you can find its static flow at another pressure with this:

F2 =

* F1
where
F2 is the calculated injector static flow (lbs/hr) at the higher pressure

P2 is the fuel system pressure (psi) you want to use

F1 is the injector's static flow (lbs/hr) at it's rated fuel system pressure (psi)

P1 is the fuel system pressure (psi) the injector is rated for





Taken from Pro-M website hope this helps also from another website i got 24lbh for 310 hp.

It would be a good time to upgrade. Since your upgrading the MAF then just buy it with a 24# calibration. My car ran lean with 19's (heads, cam, etc.). Just couldn't get it to run right until the 24# upgrade. Not saying that will happen to you but it happened to me.

im getting 24# injectors with my mods in my sig + the waiting to be installed mods, i dont think it should hurt or hinder my performance if the fuel pressure is adjusted right...

you could prolly get by either way....i had the 24s in hand and decided to stay 19s...the thought being the AF ratio would show if the 19s weren't cutting it and showing up as being was lean...so I decided to go with that thought and follow it thru at the dyno..
wasn't the case...dyno showed me right where it needed to be...my last run was 262RWHP....AF stayed right in the sweet spot both pulls...
I swapped over to the 93 Cobra from a stock Tmoss lower..I was going to throw the 24s on for that dyno run...guess i'll never know what they would have given....

91LX_5L said:

yea so you think im fine for now, a used chrome maf and injectors will cost me way more then the $120 im paying...will it not?

Click to expand...

I have a Pro-M 77 on mine that is set for 19s, so it needed to go back for re-cal (115.00) and i had the 24s in hand...my thought was why do the swap if it wasnt really needed...I still run the stock EEC and didnt want no gremlims because of the swap, running 24s with a 19 EEC...
We have very close mods so are you ok with the 19s as its sits...my expierence says yes...mines been dyno run like 12 times, mostly for "whats it worth" info...My question was the same as yours last year...I pretty much followed the info from guys here and on the 5.0 tech side as to whether "upping" to 24s for my mods was needed...
I figured I'll step up to 24s when i add more sack to it...as its sits im 302FWHP and thats in the 19s comfort zone

Could you not run 24 or 30 pound injectors on a stock motor if the calibration was correct?

Would 24 or 30 pound injectors not be running at a lower percentage?

I ask because I don't know, please help me out.

Based on my signature I would like to upgrade and I would like to buy injectors only once, even if I supercharge one day.

Thanks

I'm running 24lbers and I still have to bump the fuel pressure to 43psi to keep it from detonating on the 125 shot.

My car runs rich all the time, but that's partly due to the fact I run 39psi of fuel pressure too.
If they were too big, wouldn't my CEL light be going nuts on stock fuel pressure settings???

Interesting question.... something I know little about.

Using larger inj's can be done with the method of the maf falsely reporting air flow values to the pcm. It works up to a point and the larger the inj the more likely this method will not work so great. A more accurate method is to use real values in the pcm cal file as opposed to the cheat method.

The Cobra is a good example. It and the GT use the same maf and it is ok for two reasons. One of them is the Cobra or GT does not move enough air to max out the maf. The other reason is that Ford tells the Cobra pcm that 24lb inj's are being used. Take note here that Ford did not use the cheat method.

If you don't have a tuning device or chip then you have to rely on mechanical methods such as inj size, maf calibrations, afpr's and the like. Again, the larger the inj the more ineffective the mechanical methods become. You can only do so much by adjusting fuel pressure.

A good example is the power adder combos. How many times have you seen those guys dump the fmu's and move up to 42lb inj's AND tell the pcm about those big inj's with a chip or tuning device.

Our car's pcm (94 & 95) is load based where the fox cars are rpm based. When you lie to the pcm in our cars about airflow (calibrated mafs) you throw the load out of whack for all of the other tables that use load to get a reference point. The more the lie the more of a problem it can cause.

Why do you think most everybody uses 24lb inj's and ups the fuel pressure.

The two reasons are:
1. It works and you don't need a chip or tuner. A lot of people are doing it with no problems and that is a fact. Ever notice that some just don't seem to have as much luck as others with this method. See number 2.
2. When using a maf caled for 24lb inj's the load error in the pcm is not far enough out to cause a problem for some but it is for others.

After you move up to 30lb or larger inj's the drivability usually starts to suffer without making some pcm adjustments.

A couple of common complaints you hear of when using large inj's is over rich idle (read here surging, stalling, & such) and hot starts.

This is one reason that a custom tune will return the drivability and more power as well when larger inj's are used.

I've used 30lb inj's with the stock maf and a ProM 80mm maf which I now run with no problems but I have the ability to change inj values in the pcm with a Tweecer.

Just a few things I've seen with my car and by reading threads from guys with large inj's on the tuner and power adder sites.

Later
Grady

Kewl man... thanks for the info. I guess if I focus on N/A performance I should probably start saving for a tweecer or chip.