WS6FirebirdTA00

iTrader: (33)

ok so i have 28.8# injectors right now but i was told by racetronix that for 450+ rwhp i should be looking at some 42# injectors. lets say i have my car all tuned for the 28.8#ers and then i switch. is it just a matter of scaling the proper table for the injectors to get the LTFT's to where they need to be?

foff667

iTrader: (2)

scaling is the first step its not an exact science though and it still might need to be "tweaked" one way or the other to get your trims in line. But if your going from 28.8's to something that flows nearly twice as much fuel you dont wanna be running 9.0:1 at idle so thats where the ifr table comes into play.

WS6FirebirdTA00

iTrader: (33)

so the ifr table is the one that needs to be adjusted for the fuel injectors? and i would do a general scaling of it and then jsut tweak certain areas, such as idle, so i wont be sucking in so much gas right?

foff667

iTrader: (2)

i wouldnt even do that...i would scale it up or down a couple of percents at a time after you get it scaled properly initially...you can use your ve to get idle and stuff right if your running overly rich/lean.

WS6FirebirdTA00

iTrader: (33)

i think ill hit u up on aim tonight haha

Bill's 02 Z-28 SS

Hi Folks
I did a quick run on the numbers assume a stock LS1. This is what I would try - did the slow and small increment way and I logged a great deal of miles on the car.
MAP(kPa) 0 5 10 15 20 25 30 35 40 45 50 66 60 65 70 75 80
5.50 5.54 5.59 5.60 5.63 5.68 5.70 5.75 5.77 5.82 5.83 5.87 5.90 5.93 5.97 6.00 6.03
Sorry I can paste very well but I think you can see the numbers.
Bill

foff667

iTrader: (2)

theres an excel file i have that figures it out for you...ive even think hptuners has a calculator in the editor for it...i use the excel file since it does every cell for you and you can just copy and paste it over.

horist

(((New PSI / Rated PSI)^.5 ) * 3 bar injector) / old injector = % to scale

(4 bar / 3 bar) ^ .5 = 1.1547005383792515290182975610039
* 42
48.497422611928564218768497562126 = flow rate of 42lb injector (rated 3 bar) on a 4 bar car

48.497422611928564218768497562126/28.8 = 1.683938285136408479818350609796

so Mathmatically you'd wanna scale whatever your stock injectors are by 168%

WS6FirebirdTA00

iTrader: (33)

thanks guys, this is helping me understand some more tuning stuff. foff is gonna end up blocking me on aim, im gettin hp tuners next week lol thanks again!

BIRDONNOS

iTrader: (3)

hey horist i just installed my accel injectors rated at 37.1 at 43.5psi, which comes out to 42.66lb on a ls1 fuel system, so i scaled my table by 1.48 and my ltfts were all 25, so i scaled the table by a lower percent 1.15 to get my lifts in the -4 to 0 range , so now i need to know if this was the correct way to do this? as long as my ltfts are inline does this make it right?

horist

if the ltrims are in line then that's all that really matters... just so long as they're inline and you're not going lean at WOT


I think different injectors still flow differently (bosch vs FMS vs accel , etc...) I like to use the Mathmatical calculation as a basis, then adjust from there (it helps if youre LTFT histogram is already dialed in, if you add injectors and your LTFT table is fubared gets much harder to figure out if it's the VE table, the IFR table or even the MAF table (if you don't turn the MAF off))