Recently installed larger injectors and I saw the stock ifr table was at constant value across the range, so I increased it by a margin ((larger inj/stock inj)*stock values) and left it. Then when I plugged in values into a spreadsheet the values where scaled upwards slightly.

What is the purpose of scaling the ifr table in a slight curve upward?

rise in fuel pressure when drop in vacuum on the regulator for return syle fuel systems.

2 different tuners, both very popular on this site, told me that on our trucks you want to leave the ifr values the same across the board. something to do with being vacuum referenced or something like that. I think the Fbody guys scale theirs but i'm also under the impression that they are not vacuum referenced, whatever that means, lol.

are there any benefits to scaling them?

I have noticed I get higher inj pulse widths wot running a tuned maf vs SD I dont have enough knowledge to put it all together but was thinking the ifr table could help keep the wot pulse widths lower with it being scaled. Im getting the same pulse width with these 30lbers as I was with the 25lbers,WTF? I tried retuning the maf and thats not the issue its dead on as is my ve table. So why is it that my pulse width is lower running SD vs maf?

these are the scaled values I got from 0 to 80 kpa with

Injector Rated Fuel Pressure: 58
Your Fuel Rail Pressure: 58
Injector Rated Flow Rate 30


30.00052906 30.18750146 30.37332291 30.55801442 30.74159634 30.92408844 31.1055099 31.28587935 31.46521487 31.64353405 31.82085397 31.99719125 32.17256204 32.34698206 32.52046662 32.69303059 32.86468849

does this look correct

what are your injectors rated at, at 58psi? this looks right but i think the last one should be what your injector is rated at, at 58 psi then go down backwards. make since? in other words your first # should be around 29.***** then your last should be around 30. if there rated at 30lbhr at 58psi

oh shit i just hit 400 post, sorry :offtopic: continue.

what are your injectors rated at, at 58psi? this looks right but i think the last one should be what your injector is rated at, at 58 psi then go down backwards. make since? in other words your first # should be around 29.***** then your last should be around 30. if there rated at 30lbhr at 58psi

I was under the impression rail pressure should be around 60 and injector rated pressures should be the same.

What is the rail pressure on a 5.3 and inj rated pressure of 8.1L?

8.1l what? truck or marine i thought rail pressure was 58psi. like i said mine is 04 returnless so its a little diff. what i did on mine was take the stock table (stock inj's) and took the last number on there and subtracted that from the flow rate of the new injectors at 58 psi the the number i got i added to the whole table so it kinda skaled itself. i thank snake eater and i done that for both of ours but mine happen to be the same striaght across if not very very close to it.

8.1 truck injectors

no that is a good ?? becouse i have the marine ones. sorry its been so long since i've even attempted to tune anything its hard to remimber what all i did mine don't see but like 20% max it seems like, becouse my turbo isn't on yet.

thanks for the help what I did was to scale the injectors like this based off
Injector Rated Fuel Pressure: 58
Your Fuel Rail Pressure: 58 (this varies so I just took a mean value)
Injector Rated Flow Rate 30

kpa
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80

ifr
30.00052906 30.18750146 30.37332291 30.55801442 30.74159634 30.92408844 31.1055099 31.28587935 31.46521487 31.64353405 31.82085397 31.99719125 32.17256204 32.34698206 32.52046662 32.69303059 32.86468849

at wot it got the inj down to 17.5 ms which is what it is running SD puts me between 85 to 100% duty cycle depending on where I shift which isnt the best but its better than 120% which is what I was at with the stock 5.3 25lbers

this maf is a mother to tune and it reaks havoc on everything else its a saint and a devil at the same time I can run more timing and get better times and mpg with it but its such a PITA to tune anything with it on. My inj pulse width is an example of that.

thanks again for the input

are there any benefits to scaling them?

I have noticed I get higher inj pulse widths wot running a tuned maf vs SD I dont have enough knowledge to put it all together but was thinking the ifr table could help keep the wot pulse widths lower with it being scaled. Im getting the same pulse width with these 30lbers as I was with the 25lbers,WTF? I tried retuning the maf and thats not the issue its dead on as is my ve table. So why is it that my pulse width is lower running SD vs maf?


If you have a vacuum referenced regulator, *do not* build the curve. The curve is for returnless fuel systems, that do not have a vac ref'd regulator. The VRR makes the same curve when you need it based on vacuum / boost.

If you have a vacuum referenced regulator, *do not* build the curve. The curve is for returnless fuel systems, that do not have a vac ref'd regulator. The VRR makes the same curve when you need it based on vacuum / boost.

All late model GM engines have return systems on them, dont they?

no, mine doesn't, and if your stock IFR tables have a single value in them, neither does yours.

You can also check to see if there is a vacuum ref'd regulator on your driver's side fuel rail.

AFAIK, trucks went returnless in 04.

ok i had i bacwards my bad. like i said i'm a long ways from home and haven't even got to drive my truck in two months. i think they went returnless in 03 though becouse i think parish's is returnless also.

Mine is an 03 :) They must have done some returnless, and some return. Weird, but SOP for GM

this is true. i could be wrong but i could've sworn that he said it was. thats why he got the two big intank pumps instead of the inline. i think we've discussed this before becouse some 03's had it and some didn't

the stock values where not scaled they were the same plus there is a vaccume reference line attached to one of the rails. So I set the ifr table to 31 across the board.

Are the 8.1 truck injectors exactly 31 lb/hr?

Some say 30 some say over 31.x