What size injectors?

[SilverXJ]

I know most people recommend 24 lb injectors for a 4.6L stroker. However, I have tried 5 different calculators and all say I need a 27 lb injector. This is basing the input numbers on 260 hp and .5 BSFC.

24 lb or 27 lb?

[Flash]

I know most people recommend 24 lb injectors for a 4.6L stroker. However, I have tried 5 different calculators and all say I need a 27 lb injector. This is basing the input numbers on 260 hp and .5 BSFC.

24 lb or 27 lb?

24......unless your going with some sort turbo/blower.

Flash

[gradon]

I just calculated the flow rates of the FMS 24#(rated @39#) on the 49# rail=26.9#; the LT1 24#(rated @43.5psi)on the 49# rail=25.5#. The LT1s on the 39# rail =22.7#. The equation is {square root(rail#/injector rail rating#)xinjector # rating}.

[John]

As there is a recognized difference in identical models PCM's there is a little latitude I find the gray top OEM 23.2 # dial in sweet running OBDI With adjustable FPR set at 43# and adjustable map sensor set at 5.1V. If you run too large a injector, you are going to wash the oil from your cylinder walls during warm up when the O2 sensor is out of the picture, and increase cylinder wall/ring wear. For na motors I really have not found a need for larger than around 24# injectors, actually have found them a problem when going larger.
John

[SilverXJ]

24 it is then. Thanx.

[Cheromaniac]

I know most people recommend 24 lb injectors for a 4.6L stroker. However, I have tried 5 different calculators and all say I need a 27 lb injector. This is basing the input numbers on 260 hp and .5 BSFC.

24 lb or 27 lb?

The BSFC is probably nearer 0.45 so 24lb injectors will suffice. I'm running Ford 24lb'ers with stock 39psi regulator and MAP adjuster set at 5.10v. Emissions are excellent and A/F ratios are right on the money.

[AlexTJ]

I just read this and now I'm kinda worried.

I put 30lb injectors on my titan 4.7L

they were cheaper for some reason.....

should I change them NOW? what will happen???

[gradon]

Give them a shot, since you have them in. You will most likely want to use an adjustable map to turn down the voltage. I am running rich at idle with the LT1s on the 96 rail--25.5#, so I can imagine how rich the 30# are gonna be.

[AlexTJ]

Give them a shot, since you have them in. You will most likely want to use an adjustable map to turn down the voltage. I am running rich at idle with the LT1s on the 96 rail--25.5#, so I can imagine how rich the 30# are gonna be.

I thought it was running rich lol

Thats why Im heading out to radio shack right now lol

[gradon]

Also, since you will be turning the voltage down from the 5.10V, you don't need a 12v input(those who are turning the voltage up using stock injectors will need the higher 12v input to turn down), so you can use the existing voltage input to turn down. I recommend using male/female crimp ons(you can solder the wires to them too) to make it easier to connect/disconnect the adjustable map in case of whatever.

[Comanche91]

As there is a recognized difference in identical models PCM's there is a little latitude I find the gray top OEM 23.2 # dial in sweet running OBDI With adjustable FPR set at 43# and adjustable map sensor set at 5.1V. If you run too large a injector, you are going to wash the oil from your cylinder walls during warm up when the O2 sensor is out of the picture, and increase cylinder wall/ring wear. For na motors I really have not found a need for larger than around 24# injectors, actually have found them a problem when going larger.
John

John, I too am running the gray top OEM 23.2# injectors on my Hesco 4.5L stroker, and have been using these injectors for about three years now. On a recent dyno test at Hesco, the best HP/torque readings came with the adj. FP regulator set at 39#. I do not have an adj. MAP installed as yet, so it's sending the stock 5V. My mileage sucks (about 15MPG overall). I have an adj. MAP; do you think it would help mileage by sticking it in there and going to another higher (or lower) voltage? I'm running the Champion RC10YC plugs.

[John]

I would think if it was dyno turned at HESCO's it is about right.. RC10s would be too hot a plug for my motors. You might try the adjustable map sensor set to 4.9 but watch for pinging, Sounds like it is running well and mpg is your concern, it is unlikely the map voltage change will help that very much, but if you have one it might be a interesting test.
John

[John]

By the way nice truck. 3 inch lift, what size tires and what is your gearing presently, this might be a area of improved mpg.
John

[Comanche91]

Thanks John. RC10s too hot? Interesting. No pinging at all. The color looks good with these. 31" tires, 4.11 gears w. the AW4. Correct speedo gear installed. I think I'll stick in the adj. MAP just for kicks and grins and go down to 4.9 or so, but I'm with you, I'm not expecting any miracles.

[John]

Your gearing sounds good with the tires and AW4, not much to be gained there. Sounds like you have checked the RC10s for a while. the RC9s dial in sweet for me. Let me know how the MAP adjuster works.
John