I am looking to make my AFPR into a Vaccuum advanced fuel pressure regulator, has anyone done this? Any instructions/ pictures of the process? From what I have heard i can just drill and tap a hole on the side of housing and run a vaccuum line to it, but i dont want to just start making holes.

 

no one has ever made a VAFPR

 

does any one have a picture of their VAFPR, i want to see how it is hooked up.

 

Almost all modern fuel pressure regulators have a vacuum port on them... I'd bet that no one has a clue what the heck you're talking about... I don't.

 

I have an adjustable fuel pressure regulator (no vaccuum port) now on my tbi setup, but I am looking to make it a Vaccuum advanced fuel pressure regulator.

 

i havent the slightest idea what you are talking about specifically, but i know for a fact that my FPR has a vacuum port on it. what this does is keep the fuel pressure a specific amount above the manifold pressure.
at WOT, the manifold absolute pressure is 14.7 psi. when the blades are closed the pressure is significantly less. the fuel pressure needs to be a constant 42 psi above manifold absolute pressure.
thats where the VAFPR comes in.

 

https://www.thirdgen.org/forums/tbi/...-pressure.html

This post has the info about VRFPR or VAFPR. from my understanding and correct me if i am wrong the stock regulator stays at one fuel pressure regardless if its at idle or WOT, with a VAFPR the pressure changes at WOT versus idle pressure. Dont forget I have a TBI system.

 

i dont know about what you have, but the stock equipment on my car works as described.




the thing you have to realize is that there are two different pressures going on here.
you have ABSOLUTE pressure and GAUGE pressure.
first absolute pressure:
absolute pressure is a measure of pressure based on the fact that zero pressure is what is below that found in outer space... absolute zero. in other words, you cant get any lower than absolute zero pressure. there is no such thing as -1 psi absolute (psia for short)

gauge pressure:
gauge pressure is always based on a pressure difference between a specified datum and the pressure you are reading.
a pressure gauge that reads absolute pressure has been calibrated with a datum of 0 psia for example.

if you were to put a pressure gauge on your intake manifold to read the manifold pressure, you would be reading based off the datum of ATMOSPHERIC PRESSURE.
therefore at idle, you will see about 14" of vacuum.
when a turbo advertises 10 psi, it is relative to atmospheric pressure of 14.7.
therefore the turbo is actually putting out 24.7 psi, but the first 14.7 is implied, and the pressure read on a gauge will be 10 psiG (the g is for gauge, as opposed to absolute)




what does this all mean?
well, as you know, you need to have 42 psi of fuel pressure.
however, the 42 psi is based off of the MANIFOLD pressure, which is always changing based on throttle and RPM.
if you had a constant 42 psi without a variable pressure regulator, you would ALWAYS be rich at idle and lean up top... there would be no way to fix it.

you would essentially have approximately 50 psi at idle and 35 psi at WOT


the vacuum line to the fuel pressure regulator gives the fuel pressure regulator a refrence, so that the fuel pressure will always be 42 psi above whatever the manifold pressure is.

 

Wow, talk about not being clear... you should have given more detail or at least mentioned that it was a TBI, since they are totally different, this really should have been on the tbi forum

The reason that most are vacuum referenced is that most fuel injectors are mounted in the manifold and exposed to manifold vacuum, and their fuel flow is proportionate to the pressure across the injector (to be exact, to the square root of the pressure change), so you need to adjust the fuel pressure relative to the manifold vacuum to get predictable fuel flow.

In the case of the TBI setup the injector is mounted in a pod above the throttle body, so it is not exposed to manifold vacuum and there really isn't a good reason to make it vacuum referenced. Some later marine applications ran higher than the original designed fuel pressure to deliver some more fuel to the engine, and they added a vacuum referenced regulator to them to get the fuel pressure down to something reasonable at idle/light throttle, and I guess some people have been experimenting with them in street applications.

As far as converting a stock one to vacuum referenced... good luck, the can on them has a big hole in the side for the guide pin and another in the bottom where the adjustment screw is, you'd have to figure something out to cover/seal both while keeping both functional to have even a chance of it working, it will be more work than it's worth, especially if you can just buy one for reasonably cheap. Personally, I'm not sure that there is any real advantage to using one anyway unless you're pushing a lot of power with a TBI setup, which almost no one is, and then if you did, I'd probably just make a block off plate and plumb in a normal bypass regulator in the return line.

 

ok good to know, i will dial my car in with the ebl and see where i am at. Being that i didnt know much about the VAFPR and i was pointed in that direction i figured this would be the right place to ask about it.