When Is A Aftermarket Fuel Pressure Regulator Needed?

[yoshiii335]

Hello I have a r32 gts-t

I am going to buy 550cc injectors and a larger fuel pump, bigger turbo, and supporting mods for tuning the car.

My goal is about 350-400 hp.

For now I am putting a rb 25 turbo on the car and upping the boost.

The car has full turbo back exhaust, pod and fmic.

When is a aftermarket fuel pressure regulator needed?

[KiwiRS4T]

Hello I have a r32 gts-t

I am going to buy 550cc injectors and a larger fuel pump, bigger turbo, and supporting mods for tuning the car.

My goal is about 350-400 hp.

For now I am putting a rb 25 turbo on the car and upping the boost.

The car has full turbo back exhaust, pod and fmic.

When is a aftermarket fuel pressure regulator needed?

Stock will be fine for your plans.

[GTSBoy]

When is a aftermarket fuel pressure regulator needed?

Almost never.

[Blackkers]

You need an aftermarket fpr when the factory one won't fit. ie, if you upgrade your fuel rail.

Not many other reasons to change it

[yoshiii335]

Thanks everyone.

So when I put in larger injectors I do not need to adjust for the increased flow?

[89CAL]

FPR is about keeping pressure in the rail not flow. Choosing the right injectors means you should never have to change the fuel reg unless as stated you have an aftermarket rail and the stock one won't fit

[ARTZ]

Or you want to be able to adjust your fuel pressure...though usually there is no need it can be a useful tuning tool

[discopotato03]

Or when the bypass hole in the standard one isn't large enough to stop fuel pressure rising at light loads and idle with higher volume pumps . In theory any reg can close right up but standard ones can only open up so much .

A .

[Ben C34]

Or when the bypass hole in the standard one isn't large enough to stop fuel pressure rising at light loads and idle with higher volume pumps . In theory any reg can close right up but standard ones can only open up so much .

A .

True in theory.

Do you have any examples of that occurring?

[scotty nm35]

True in theory.

Do you have any examples of that occurring?

Exactly, even though the hole in the stock reg is small, it doesn't seem to cause the pressure to increase from my testing, even with the Walbro 460's at full noise. Perhaps with a 2000hp pump, but you would need new rail and reg with braided lines by that stage I think.

[Blackkers]

Exactly, even though the hole in the stock reg is small, it doesn't seem to cause the pressure to increase from my testing, even with the Walbro 460's at full noise. Perhaps with a 2000hp pump, but you would need new rail and reg with braided lines by that stage I think.

So the 460 walbro will support around 450rwkw on e85 and won't flow too much for the stock fpr?

and it's $200 brand new, sounds like a winner for most applications

[scotty nm35]

So the 460 walbro will support around 450rwkw on e85 and won't flow too much for the stock fpr?

and it's $200 brand new, sounds like a winner for most applications

And is long term e85 tolerant. It's a no-brainer for most applications, or until a surge tank is required, eg track work.

[Trex]

The only reason to "upgrade" the factory FPR is really in three instances:

1. When your injectors are starting to max out, but you don't want to upgrade them, so you bump up the rail pressure with the aftermarket adjustable fuel pressure regulator to push them a little but furthur. Obviously this isn't ideal and most people don't recommend it. Just buy the correct injectors to start with.

2. When you are running huge amounts of boost and the factory fuel pressure regulator can not keep up the 1:1 fuel pressure ratio. Therefore you will need an aftermarket fuel pressure regulator that can handle this high amount of boost pressure and keep up the 1:1 ratio.

3. The factory fuel pressure regulator has failed so you may choose to buy an aftermarket one however still run it at factory fuel pressure.

So as you can see, not many people fall into the second category because a lot of people don't run 2+bar of boost through their car. A few do fall into the first category because they may be on a budget and don't want to upgrade the stock injectors so they choose to bump the rail pressure up instead and obviously a few will fall into the third category.

However there is a fourth category that you will find 90% of people with aftermarket fuel pressure regulators fall into:

4. They have no idea what an adjustable fuel pressure regulator does, but they got told to buy one by a mate or read about one somewhere.

For your situation assuming that you are not running E85, your 700cc injectors should be fine for between 400-500HP therefore you do not need an aftermarket fuel pressure regulator.

[scotty nm35]

Quote:

The only reason to "upgrade" the factory FPR is really in three instances:

1. When your injectors are starting to max out, but you don't want to upgrade them, so you bump up the rail pressure with the aftermarket adjustable fuel pressure regulator to push them a little but furthur. Obviously this isn't ideal and most people don't recommend it. Just buy the correct injectors to start with.

2. When you are running huge amounts of boost and the factory fuel pressure regulator can not keep up the 1:1 fuel pressure ratio. Therefore you will need an aftermarket fuel pressure regulator that can handle this high amount of boost pressure and keep up the 1:1 ratio.

3. The factory fuel pressure regulator has failed so you may choose to buy an aftermarket one however still run it at factory fuel pressure.

So as you can see, not many people fall into the second category because a lot of people don't run 2+bar of boost through their car. A few do fall into the first category because they may be on a budget and don't want to upgrade the stock injectors so they choose to bump the rail pressure up instead and obviously a few will fall into the third category.

However there is a fourth category that you will find 90% of people with aftermarket fuel pressure regulators fall into:

4. They have no idea what an adjustable fuel pressure regulator does, but they got told to buy one by a mate or read about one somewhere.

For your situation assuming that you are not running E85, your 700cc injectors should be fine for between 400-500HP therefore you do not need an aftermarket fuel pressure regulator.

Or 5: You want to lower the fuel pressure, as 40 psi base plus 40 psi boost is getting way too high. Most pumps have issues supplying fuel at 80psi+ pressure, lowering the base pressure will allow much greater fuel flow from the pump, as long as you didn't cheap out on undersized injectors.

[Blackkers]

And is long term e85 tolerant. It's a no-brainer for most applications, or until a surge tank is required, eg track work.

awesome, Even for track work though can't you just fill the tank to the top and not worry about surge? Or am I missing something

edit:

Quote:

Or 5: You want to lower the fuel pressure, as 40 psi base plus 40 psi boost is getting way too high. Most pumps have issues supplying fuel at 80psi+ pressure, lowering the base pressure will allow much greater fuel flow from the pump, as long as you didn't cheap out on undersized injectors.

That's also a good point. I'd contact the injector manufacturer and see what they think about running less than 3Bar base. I wouldn't trust the spray pattern at that pressure without having them tested.

Or is that a waste of time?

Edited July 6, 2014 by Blackkers

[Ben C34]

If you were running 40 psi boost I don't think low load spray pattern would be a concern at all!

[scotty nm35]

awesome, Even for track work though can't you just fill the tank to the top and not worry about surge? Or am I missing something

edit:

That's also a good point. I'd contact the injector manufacturer and see what they think about running less than 3Bar base. I wouldn't trust the spray pattern at that pressure without having them tested.

Or is that a waste of time?

My tank is 85L, you don't want that sort of extra weight in a track car.

3 bar is a lot, I run around 35psi base. Most injectors have issues opening consistently at high pressure too.

[GTSBoy]

If you were running 40 psi boost I don't think low load spray pattern would be a concern at all!

Yeah, but remember that the delta P across an injector is constant (or at least it's supposed to be - rising rate fuel pressure regs or improper operation of the reg notwithstanding) at all loads. If you lower the pressure to keep the absolute pressure under control at high load, then it is also low at low load.

What you would want, if such a thing existed (and it does, just possibly not in the automotive field) is a falling rate reg.