Fuel Injectors - 30's too big?
 

OK,

I'm trying to match up an engine combo so I can rush out and buy it before my wife takes away all my money :)

So far it looks like this:

TFS Heads (most likely out of box)
TFS Street Heat Intake
New Cam - Something with a lift around .5
70mm TB
75mm MAF

Which injectors? 24's or 30's. I'm leaning to 30's as I've heard the Pro-M MAF doesn't work too well with the 24's. Plus if I ever have the intake and heads ported I don't want to run out of fuel.

No 30's should be just fine.

I don't think you would run out of fuel with the 24's - even if you do port the heads/intake. Just my opinion.

I have heard the same thing about the problems with the Pro-M MAF & 24# injectors - however, I have this setup and have no issues. ???

Good luck,
E

You won't be running out of fuel with 24s even if you get the heads and intake ported. Just get an adjustable FPR to go with them.

30's would be just fine, Holley does recommends them for their systemax kit. They would be the better choice, especially if you add a power adder down the road.

Thanks guys. I won't be adding a power adder yet, but I'll also be paying off the car completely and down the road I should be able to convince the wife I need ;) to get a blower.

Fuel pressure won't be too low would it? I don't know what the minimum fuel pressure needs to be to maximize performance.

I'd say your minumum fuel pressure would be like 37psi with the 30's and an aftermarket fuel pump. You probably would not run out of fuel with the 24's, however if you create a great combo like Skyman and pull 330rwhp then 30's would be a great idea. The only way you would max out your 24's would be by getting a custom tune (recommended) and adjusting the pulse width and duty cycle.

But if you ever want to go with Nitrous, 30's would be better. ;)

Keep in mind that with a Ford based MAF, the meter reads up to 4.8 volts accurately (I think it can go to 5 volts max), with that in mind, a meter calibrated for 24# injectors will lose resolution on anything putting out about 350 hp or better at the crank. 30# injectors are good for 430 hp in the same scenario.

It's interesting to note that 19# injectors at about 230 hp are only pulling about 4.5 volts. which I suppose is food for thought seeing as how a 5 liter from the factory produced 225 hp in its prime

On another note 24 lb. injectors are good up to 450hp "supposedly".

Dont forget a new fuel pump too, and a regulator.

HA! **cough** BULLCRAP **cough** And the king cobra clutch can hold 400hp no problem. :rolleyes:

Im running 30's and they are just fine. You will need a custom chip though. I bought the 30's because I plan to squeeze a few horses later.

MM&FF says that you can never go too big with an injector. Im not sure if thats true but thats what they printed. Though if you use the Mustang Analyzer on this site it will tell you that with 30's you are over injected.

But Im running them and they are working fine for me. BTW I killed another LS1 tonight on the freeway. He was really sore about it too.:D

Well with my combo the 24# weren't enough up top so I went to a set of 30# and man was there a difference, nice smooth power curve and it doesn't go lean up top no more. I run 40psi of fuel pressure.

You will need atleast a 190lph fuel pump to feed the 30#, a 155lph just doesn't cut it, trust me been there done that.

I say get the 30#'s I hate buying parts twice;)

I say go with 30#'ers, even though the 24#'s are "rated up to 450hp" too many people have experienced they aren't enough for moderate hp combo.'s. Hence Holley suggests 30#'ers with their systemax kit.

Thanks guys, 30's, adjustable fuel pressure reg., and a 190 lph pump will be in my combo. :cool:

I suppose if you crank up the operating pressure, the injectors will support 450 hp? but the system is designed for a lower operating pressure (as well as a shorter duty cycle) and raising it knocks things out of wack if your using stock electronics which try to compensate for the irregular injector flow.

The computer could actually care less about how much hp the engine makes, how much air it needs, or how much fuel it needs or even how big the engine is. Heck it could care less what type of engine it is on (well within the realm of 8 cylinder 4 stroke internal combustion engines)

What it sees, is the MAF is using this much voltage so I'll compare this to the voltage from the the throttle posistion sensor, and what RPM the engine is turning and apply voltage this long at the injector so when I check the voltage from the oxygen sensor it should compare with the table and look like this. Leading the computer to say "kewl" or "opps".

When Ford designed the table, they had a specific pressure operating range in mind so the injector would flow this way when there was this much manifold pressure observed. Cranking up the pressure at the injector changes its flow characterisitics, which forces the computer to alter its operations in order to comply with the table Ford provided as best it can.

The whole trick to selecting an injector and a meter is to maintain resolution within the operating range the sensors were designed to accurately read

injectors
 

Geez, I'm still running 19lbers with AFPR and 75MM mass air. But if you want a power adder later go with the 30's, that is what I will be doing.

WITH 19# INJECTORS! GET EM OUT OF THERE MAN, IT'S TIME FOR 30#'ERS.