Injector question

[IanSzgatti]

hey... my co-worker has 60 lbs injectors that he's offered me. Now im wondering... the computer doesnt change, it just pulses the injectors like they would my stockies... but when the 60 pounders open, the allow more fuel... is this right???

it'sa a friggen miracle... he's got these injectors for me, plus upper and lower manifolds from a 3400... i am truely blessed... it's all free! This guy started at our shop like two weeks ago... anyways... I tried to tell him about the coolant line fitting and all this, and he's got scads of parts galore... it's like I just won the fucking lottery!!

[JMo60]

60lb is pretty much huge. actually its outrageous for a 3400. There will need to be insane amounts of tuning, and even then it will pry run like junk... Where did 60 lb-hr injectors come from??

[IanSzgatti]

thats what i thought.... i'll find out where he gottem from... but with this guy, I believe him when he says they'd work... or else he's not 100% and assuming... i'll find out more tommorow

[sprucegagt]

I would only use 60 lb injectors on a HIGHLY modified engine. That's alot of fuel for a 3400/3500. I think Tejohnson has a set and he said that idle quality really becomes a problem.

[IanSzgatti]

so with that amount of fuel i'd probably foul everything up.... you know, the guy is a mechanic, so i don't doubt he understands that these things will fit... but i dont think he knows precisely what injector would be a good upgrade... as i understand it, I have a 19lb injector now...

so if this dudes got some other shit for me.. what would be more suitable as an upgrade? 26? 30+? I want them to spray as much as possible, without causing to much harm... idle a fraction poor, I can handle... but I want this thing to be good at 4000+ rpm... someone teach me something here....

does a stock 3400 have the same 19lb injectors as a 3100?

[sprucegagt]

3100/3400 had 19 lb @ 43 PSI fuel injectors up to 99. Starting in 00 it increased to 22.5 lb @ 50 PSI.

As for a good upgrade, well it depends on your mods. Right now I would say GTP injectors would be the max if you got a cam, UIM/LIM, heads, headers, CAI and 65 mm TB. Even then, they are a little overkill. But a little nitrous can cure that problem.

[JMo60]

you are aware that when you using larger injectors, tuning is mandatory?? if you dont tune it, you will be dumping "willy nilly" amounts of fuel

[IanSzgatti]

i should at least be going to 25lb.. 30 something would probably still be ok... without tuning... i dont see why the cylinders couldnt handle that with all the manifold and intake and exhaust work...???

[JMo60]

i should at least be going to 25lb.. 30 something would probably still be ok... without tuning... i dont see why the cylinders couldnt handle that with all the manifold and intake and exhaust work...???

Um, yeah... air fuel ratios..

[Superdave]

Im using 36lb injectors running at about 70% duty cycle @ 315 crank HP


There is no way in hell my engine would even start if i was using these injectors on the stock tune. my BPC is WAY different..

[IanSzgatti]

ok... good enough for me, except that your only saying.... "air fuel ratios" without giving further info.... like why the 02 sensors cant compensate and bring the rich mixture under control.... If your flowing more air, the 02's will do what?... richen richen the mixture... if your flowing more fuel...etc, you get the idea. I know to some degree my stock tuning can compensate for more or less fuel, I'd just like to know how much

JMo60, dont leave me hanging with incomplete remarks. back up all your statements. my question initially is about injector sizes... knowing now it's not possible to go to big on my stock tune, tell me... is 25lb ok without tuning, concidering the modifications i've listed.

[JMo60]

ok bud, your car will somewhat compenstate at part throttle operation, but the tables in the mapping of the computer only go so far.. with injectors that large, your computer will be comanding as far lean as it can go, and you will still be injecting too much fuel.

At WOT, your computer kicks into "open loop" mode, which means that your oxygen sensor is not being used as an input to your computer. The computer adjusts fuel from the other sensors without the o2 input, so you will still go super rich.

by the way, what mods do you have? give me some details on the car, and maybe i can lead you in the right direction

any time you go to bigger injectors, you will need to tune. 25 lb injectors might get the car running on a stock tune, but it will still not run "correctly". your best bet will be to obtain some means of tuning and get a wideband

[IanSzgatti]

Ok, making a lot more sence to me now... im understanding. I'm talking about mods to a 3100 (1997) with ported 3400 manifolds (TB 56mm), an intake, and low restriction exhaust.
I still have the same heads though, so I know thats kind of shity. Thing is, even the things I have done to it so far have made a noticeable (though not really impressive) changes; mainly throttle response.

I figured that since I'm spooling up so nice and fast, a little more fuel would be good. What your saying makes sence... I'd need to see some numbers, but something tells me the 2000+ injectors for the 3100 would be alright... i'll bet the 'tables' are different though, so maybe not... im no expert on these things like you guys.

Mainly what I do as a mechanic is all the general day to day repairs. I know what sensors do, can diagnose and test them... but really, if your not having to tune a car for modification or performance, you never really get to look so in depth at these things as an inter-working system.

I'm really impressed with your knowledge... I respect your opinions, and apreciate the time you take to reply. I just don't want anyone to get the wrong idea here... i'm not just throwing around ideas for nothing... i am totally a student here.
Anyways, I've listed what I've done. Obviously it's never enough though... do i now have to shell out 400+ bucks for a DHP tuner or something? or just bite the bullet and order a custom PCM?

[91parkave]

In all honesty, You dont need injectors with your mods, and yes shelling out 400 for a powertuner is the best investment. Until you can scasn the car a couple of times and know what your injector,s are actually doing, plus your o2 counts, okus your short term,long term fuel trims, Knock counts...etc otherwise a factory tuned car is on the rich side anyway so youll be fine with the mods you have. i wouldnt recomend any kind of injector upgrade until a cam or ported heads...just my .02

[JMo60]

you could use an apexi safc or something to tune if you have to, its not as good as DHP, but it should get the job done. i really dont think with your mods you will need bigger injectors yet.