The 454SS does it again. Little G's turn...

[JL8Jeff]

You kind of made my point, the vrfpr gives a full 18 lbs of fuel pressure at full throttle(or lowest vacuum) and the stock fpr is only around 13 lbs and the other adjustble fpr's are around 15 lbs. So the vrfpr could be supplying more fuel than the others and give you a better idle to help pass emissions. As for the mods Tim said he already did to it, have you put a fuel pressure gauge on it to see what it's really getting at the injectors? I never installed it on my truck so I'm not sure what pressure I was getting. And I believe the 90-91 454 trucks had the 90 lb injectors so there's nowhere to upgrade to. Just a thought on getting more fuel into the engine.

[Fasterthanyou]

Originally Posted by JL8Jeff

You kind of made my point, the vrfpr gives a full 18 lbs of fuel pressure at full throttle(or lowest vacuum) and the stock fpr is only around 13 lbs and the other adjustble fpr's are around 15 lbs. So the vrfpr could be supplying more fuel than the others and give you a better idle to help pass emissions.

That makes no sense. How did I make your point and where are you coming up with the vrfpr giving 18psi? Stock is not always 13 and the adjustable's can be anywhere you want them to be, not stuck at 15!!! There are some stock regulators running 22psi, there's one on my Dad's suburban right now.
I think you need to re-read my post, you might have gotten some numbers mixed up or something.

[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.

[Tru2Chevy]

FYI - Matt has a nice electric fuel pressure guage, however he hasn't bothered to hook it up yet....

- Justin

[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.

[JL8Jeff]

Yes, I was looking at it from a point of no custom programming so the vrfpr looked like the best compromise. Did Matt see that Turbo City has the overbored 454 throttle bodys at 2-1/16" bore instead of the stock 2" bore. That could help with the extra flow he needs. He still might be maxxed out on the injectors or fuel line though.

[Fasterthanyou]

Originally Posted by JL8Jeff

Yes, I was looking at it from a point of no custom programming so the vrfpr looked like the best compromise. Did Matt see that Turbo City has the overbored 454 throttle bodys at 2-1/16" bore instead of the stock 2" bore. That could help with the extra flow he needs. He still might be maxxed out on the injectors or fuel line though.

He shouldn't need more than the 2" TBI. That's equivelant to a 51mm EFI throttle body. Last time I checked the RamJet 502 was using a 48mm TB and had no problems . TBI is almost always fuel limited. When you get to about 350hp that's when you wan a 2" TBI, at about 450 the largers might help, might not. I would consider the TBI upgrade a waste when he hasn't gotten the fuel traightened out yet.

[DieselKickYoAss4Sure]

throw a ****ing carb, on it a blower in between would be nice, and a better rear god damnit all. Because as soon as he starts to hit that lucky number 12 its gonna break into a few.............hundred peices. Ill have to get the duelly running wish i was home i think i can trap at the same speeds. Conversations between my father and I have touched the surface of propain injection then ill be pulling both fronts of the ground big smily faces across the screen.


OH AND JUST FOR ALL YOU WEIGHT NAZZIES ITS COOL AND EVERYTHING WHAT YOUR DOING BUT THIS JUST PROVES IT CAN BE DONE WITH AC. TRUCKS ****ING RULE

[foff667]

Originally Posted by DieselKickYoAss4Sure

throw a ****ing carb, on it a blower in between would be nice, Â*and a better rear god damnit all. Because as soon as he starts to hit that lucky number 12 its gonna break into a few.............hundred peices. Ill have to get the duelly running wish i was home i think i can trap at the same speeds. Conversations between my father and I have touched the surface of propain injection then ill be pulling both fronts of the ground big smily faces across the screen.


OH AND JUST FOR ALL YOU WEIGHT NAZZIES ITS COOL AND EVERYTHING WHAT YOUR DOING BUT THIS JUST PROVES IT CAN BE DONE WITH AC. TRUCKS ****ING RULE

did you take your meds today phil?

[DieselKickYoAss4Sure]

Originally Posted by foff667

did you take your meds today phil?

no sorry i forgot