[Fasterthanyou]

Originally Posted by JL8Jeff

OK, let me explain this the way I thought it works. I'm probably wrong so correct me if I am. The fpr "sets" the fuel pressure at a specific level. Let's say stock is 13 lbs. So your TBI is allowing 13 lbs of fuel pressure to the injectors at all times. The computer tells the injectors to stay open longer or shorter depending on the throttle position. So you now have a set limit on how much fuel it can flow based on the 13 lbs of pressure and the injector pulse width. An adjustble fpr allows you to adjust that pressure between 8-15 lbs say. So you set it at 15 lbs and obviously get more flow at WOT. The vrfpr automatically adjusts the fuel pressure from 8-18 lbs depending on the vacuum signal so WOT would be giving you 18 lbs of pressure which should be flowing more fuel. I know several people have measured the vrfpr at WOT at 18 lbs so that's where I'm getting that number. Now, is there a fuel pressure sensor somewhere in the TBI that the computer reads and can be programmed? If so, I'm not aware of it.

Jeff, that's not how it has to work but it is how it can work. I think it's easiest if I just tell you what I've done to my car and it might make you think twice about those crappy VRAFPRs.
I had 12psi, it wasn't enough for 330hp so I tried cranking up the fuel pressure because lucky for me, the holley fpr is adjustable. It goes up to 15psi and then anything after that causes the pressure to spike up to 50+. I was bottoming out the spring. Okay, get a larger spring, install it and I've got 28psi . Now here's the kicker, I can still control my idle! I don't need lower fuel pressure at idle because I've adjusted my calibration acordingly. Now when I hooked up the VR to my AFPR the fuel pressure went down at idle but my tables in my calibration looked all fubar (because the injectors don't SEE manifold vacuum so pressure differential has just changed). This is why I hate them and why nobody should ever need them if you do the tuning that is needed.
So here's the low down; stock regulator 13psi, AFPR isn't 11-15 it's more like 8-20 as a range, VRAFPR is the same as the AFPR only at idle it pulls DOWN the fuel pressure. Both the AFPR and VRAFPR will flow the same amount of horsepower supporting fuel but the VRAFPR will work best if you haven't touched the calibration, the AFPR will work best if you have.