Confusion about IFR---flat or sloped.

[coachcrow56]

ON my GTP, I use a Fuel pressure regulator that uses vacuum and is set at 52psi at idle. Do I need a flat IFR table (numbers all the same) or a sloped table?

[murphinator]

with a rising rate regulator that goes +1lb fuel pressure for every 1lb of boost I have seen posts that it should be flat , meanwhile with the same rising rate regulator in place as oem the factory tune is sloped....

not much help I know more just giving some background as to the varied answers you may get

[coachcrow56]

My original stock tune had a sloped IFR table. I just need to know if I need to switch to a flat table.

[murphinator]

your running 42.5's ? I dont think there is full characterization for any injector that size so your going to have to hack the tune to some extent whether its through IFR , maf , adders , etc.. or a combo of them.

If your running those injectors and tuning around them then then you have chosen that path and just try your best to hit safe AFR's and to keep trims close to in line so they dont carry large corrections into PE which these cars will do.

I am not judging - thats what I have been working with myself until I change injetors and take another crack at it....

[GTPpower]

I've always used a sloped table with good results. But, I know people that use the flat table without problems either.

[Trent_Petersen]

I worked with Injector Dynamics for a little bit to get the tune for my 115Lb/Hr injectors all squared away and they suggested using a flat table, since the FPR is boost/vac referenced.

Either way I have almost no issues with the 115Lb/Hr injectors in the car, other then the need to spend lots of money to get the IDC above 25%.

[passingpower]

If you look at the first model year M-90 GTP ('97 from the repository) The IFR was flat. That is how the calibrators thought it should be with a vac ref rail. They soon discovered the #18 wire powering the fuel pump wasn't up to the task at WOT. Too little voltage and current delivered under peak demand so, the pump pressure sagged and with it fuel flow. Under those conditions, a flat IFR was a miserable fuel model. GMPT hacked the tune to compensate saving the cost of stocking and installing heavier wire just for the pump.
I'll provide links later that explain in excruciating detail.
http://www.hptuners.com/forum/showthread.php?t=35026
http://www.hptuners.com/forum/showthread.php?t=36722
Bottom line: Stock #18 wire, use the factory slope. Its ok to use linear math to scale it from there. Yes, I realize That method will yield a trash fuel model but hey, it was hacked from the factory. If you upgrade the FP power cable, that will allow you to use a flat IFR as the designers intended and model the fuel characteristics correctly. Now why would anyone want to piss away all that effort by blowing it using linear scaling? Use Bernoulli's fluid flow equation and do it right. be sure to get the correct specs for your injectors and use the VCM suite injector calculator.