Question about safc and fuel control

[uncle_louie83]

ok....i know the safc can control fuel injectors twice there size...our stock injectors are 260cc injectors....so with the safc i can go to 520cc....I was wondering what would happen if i put 550cc injectors on this...how would it affect my idle...i heard 10psi over base fuel pressure is like 25cc....our stock fuel pressure is 42.5psi....well 550cc is 30cc over....all i need is some insight...im not so worried about gas...im more worried about idle...i need someone who is an expert in this sort of field...or someone who can just plainly help me out. will i be ok putting 550cc on an safc?

lewis

[DRIFTEADOR]

im pretty sure the stockers are 270cc so in theory 540cc is the biggest a safc could control. however, the ecu can correct for some fuel in closed loop operation (you wont need full -50% correction except at idle anyways). I'm almost positive even 600cc would be fine. I know there are some here running at least 550's on a piggyback.

[Checkered-Member]

Can I ask why are you running such large injectors

[Import_Ant]

Can I ask why are you running such large injectors

cuz when u run teh nitrous and turboz you gotta have all kinds of fuel!

seriously though there's a guy selling RC DSM style 550cc injectors locally for 150$... might as well overcompensate now if you have grandiouse plans for the car in the future

here was my reply on the other site though:

Quote »after some research:

since the SAFC can only adjust injector duty cycle UP TO 50% +/- it would seem like the idle would be very rich if you could get the car started at all. it is possible to add an aftermarket FPR (like the Nismo) that replaces the stock FPR and reduce fuel pressure to compensate. I think the Nismo FPR is only a 1:1 rising rate FPR though. Anyhow if your not pushing the 550's to within an inch of their life and you have an adjustable FPR, I'd say it's do-able since you're going to have to push them more since you are at a lower level of fuel pressure, or add an 5:1 FMU in as well. but that kind of defeats the point and if you're getting a good deal on the injectors, you are negating that by spending more $$ on the FPR and FMU.

I'd say for what it's worth on your application (and mine for that matter) don't get bigger than 520cc injectors unless you are planning on buying those items right now anyway.

now someone else plz chime in and offer another opinion

(edit) here's where I got the 5:1 FMU from:

if your info is right and every 10psi in increase over base fuel pressure is like adding 25cc to your injector's capacity, the same would work in reverse. so you're dropping your base fuel to approx 32.5 psi. now as you increase your revs (we'll assume you're going to push 15psi) now you are raising your fuel pressure 5lbs to every 1 lb of boost. by 15psi your fuel pressure is increased to 107.5psi. still allowing you to use your injectors at mid-to-minimal duty cycle but not stressing your fuel lines/system past their limits (edit)[/quote]I didnt think about the ECU's ability to compensate too... hmm..

[Florida240sx]

I'm fixing to be running tomei 555cc on my SAFC II. It can handle past but just isn't recommended because past that point it doesn't control as effective. Our stockers are 260cc side feed

[uncle_louie83]

yes the stockers are 260cc...now if they were 270 then id be more then happy to buy some 550's when i finally need them. for now my 450cc injectors will compensate just fine. all in reality with 555 tomei injectors you will be 35cc's over the capacity...only if i could find a set of 550's to just experiment with...oh and aaron...i know since the dsm injectors will need resistor packs, if you end up getting a set like i did i can get you a resistor pack for like 5 bux...so let me know if you need one or not when the time comes. i know a place with an abundent supply of them. anywho i think if i can ever find some 520cc injectors i will go with them until then ill go with what i have.

lewis

[Checkered-Member]

yes the stockers are 260cc...now if they were 270 then id be more then happy to buy some 550's when i finally need them.

no....stock injectors ARE 270cc

[uncle_louie83]

read it and weep

Side FeedEngine Style Size Impedance* Years / ModelsNissan KA24DE Side feed 260cc High S13/S14Nissan SR20DET Side feed 370cc High S13/S14Nissan SR20DET Side feed 480cc High S15Nissan RB25DET Side feed 370cc High R33/R34Nissan VG30DETT Side feed 370cc High Z32

this right here is from WDracing....if you look in the main ka-t directory under injector spread sheet...you know the top thread...its a sticky.

if we had 270 id be happy but 260 is what we have.

lewis

[Craving4Boost]

260cc or 270cc...an AFC will work just fine with 550cc's..but your going to have a different MAF right?

[uncle_louie83]

yes im going to get a z32 maf....BUT...i only need that maf when i increase the hp....the safc will control the injectors....so what i am going to do is put the 450cc dsm injectors on the car with the ford 4.6L fuel rail and the external FPR i have and go that route....once that is all up and running on the engine in all motor stock format then im going to add boost with the z32 maf and retune for the amount of power i am pushing.

lewis

[Craving4Boost]

go for it..sounds like you know what your doing