i recently had 30# injectors with the largest disk (no ring) in my sfmu... the car ran great, but at higher boost would lean out a little bit....so i went with the 40# injectors and kept the same disk/spring combo in. it runs, but not as great...my egt's are great, but its not smoot. if i mash it, it would hesitate and sputter, then take off. i believe the car is running to rich. so i put the disk/ring combo that was a little smaller (not sure what ratio)...and now i think its running to lean.... any help? i also have these questions.
- what are the disk/ring combos that i have (ie: 2.72 etc...) i dont know which is which
- i dont have a dark spring....is the spring only to help with idle?

thanks

I run the second to smallest ring/disc combo with the short dark spring and bleed valve on 42# injectors. I maintain a 14.7 at all vac/boost points and 10.5-11.5 @ WOT. You are probably still running too rich with the 2.72 disc especially if you do not have a bleed valve. The spring is mainly for idle adjustments but I believe it also slightly alters the fuel curve. Also you cannot achieve a proper fuel curve without proper idle fuel pressure. I run 15-18psi FP at idle so I'd target around there.

what are your STFT on those 42's with the fuel pressures like that. I have 40# with 10# of fuel pressure and have STFT around 0. Also have good WOT AFR around 11.5. 10.5 is really rich

I really can't get my idle pressure any lower, even if I remove the spring. I'm unsure of my STFT's, I only use the wideband anymore. 10.5 is rich, but it run's ok. I can get it leaner with the bleed valve, but it is unstable day to day... so I don't bother to tune it unless I hit the track.

yeah, my stft were pegged all the time at -25... i cant get my fuel pressure any lower than 25#...i believe its because my stock return line is too small? so you said the second smallest ring? what rate is it...what rate are the other rings?
thanks

Just for reference...what were your idle and WOT FP's when running the 30#?

I am running the SFMU, wablro 255, and 30# on 8psi of boost. My idle FP is 30psi and WOT is 80psi. I think I need to lower my rise rate to 8:1, but I'm not 100%. I wish I had a wb to help me out. I know I have to be running rich.

Yeah, you need to lower your idle pressure (and get a wb :D). I ran 32# for a couple of years at ~20psi idle, and the 2.72 disc was close to perfect when I got the wb. I believe I still had to use bleed valve to get WOT AFR tuned better, was still a bit rich w/o bleed but it ran good.

i have tried the biggest disk, next biggest disk, and the 2nd smalles disk like you said and none ran good at all. the best performance was from the biggest disk/no ring. it runs good and egts are good, but theres a little miss. with the other ring/combo, it bucked real bad and wouldnt accelerate....i was too nervous to hit it hard so i dont even know what fuel pressure i was seeing max. i want to calculate it so i know what to shoot for...but i need to know what ratio disks i have. thanks
doug