It raises the fuel pressure. The fuel pressure regulator is nothing more than a restriction in the fuel's return path to the tank. The manifold pressure acts on it to change the size of the restriction but it's no more complicated than that. When you put a larger amount of liquid through the same size hole you get higher pressure. When you put in a higher flow fuel pump you get higher fuel pressure.

:rolleyes:

excerpt from 1st section (installation overview) of first page of stage2v4 instructions:

"With switch in off position or no switch connected vehicle will run on code optimized for premium unleaded and no forced induction. If you do not wish to use the second version of software housed in the memory adaptor it is not necessary to install a switch or any additional wiring."

Whoo, don't agree with that mate. The pressure regulator will out put the same pressure, regardless of the input pressure. There is a spring in there that acts against the pressure on the inlet, this spring pressure is modified by the manifold pressure, to alter the restriction size, to ensure the out pressure remains the sum total of spring + manifold pressure.

The flame on your welding torch doesn't change as the bottle pressure gets less. :)

Harvey. ;)

Harvey,
That's the way I was taught that pressure regulators worked...
-Bill

That's my understanding too. Everything I've read is that if the fuel pressure goes up with a larger fuel pump, then the fuel pressure regulator is being overdriven beyond its capability. This results in improper fuel pressure control.

well, according to the fuel pressure guage on the fuel line the pressure went up. I believe i even put pictures of it up at the time.

Michael,
I don't recall seeing any picture...but then my memory isn't what it used to be :rolleyes: :D How much did the pressure "go up"? As Mychalio mentioned, you're probably just over driving the stock fpr which means you're applying load to the internal spring that, while probably covered in the spring's design margin, is taking the fpr out of its most efficient operational "band".
In a "bigger picture" sense, what are people more likely to replace, the fpr or the fuel pump? Personally, I'll take the fpr over dealing with electrical wires going into a container of liquid TNT every day of the week :eek: :D
-Bill

You are right, I didn't put up pictures. I was confusing the pictures I took during the original stage 2 installation and the stage 3 prototype write up where I described the raise in fuel pressure after the installation of the 255lph pump. I'm not advocating that anyone replace or not replace their fuel pump just trying to answer the question that was posed to me questioning the information I shared. The fuel pressure is raised and the fuel pressure regulator does still effect fuel pressure according to manifold pressure as designed. I certainly don't want to fuel sensless debate about the engineering of a fuel pressure regulator but in case anyone feels they just can't let it drop without understanding the physics behind it. The way I see it is you are dealing with a vector of 3 forces acting upon the size of an opening. The size of the opening restricts the flow of fuel which effects the pressure of the fuel. The fuel pressure is on the supply side of the opening not the output side. The output side is just the return to the tank. It's impossible for the magnitude of one of the forces not to effect the size of the opening and thus the increase in fuel flow must increase the opening size; however, the increase is not so large that it allows the almost twice as much fuel to pass through in the same amount of time necessary to keep the pressure the same as with the prior pump.

That's how I imagine it works. I could be wrong. However it works the effect is the same. I measured it. In any case I'm not advocating the use of any given fuel pump or fuel pressure regulator. I designed the stage2 v 4 software to work with all the available fuel supply scenarios. Since the v4 revision solves the fuel injector cap problem no matter which fuel supply scenario you have I'm personally done with fuel supply discussions.

This thread is dead I think. Stage 2v3 no longer exists. The stage 2v4 write up is at http://www.subaru-svx.net/forum/showthread.php?t=28023

Please try to keep it relevant to stage2v4 though.