At what point is a FP regualor needed? I am running 1000cc injectors on a 50 trim and a 100 shot of dry nitrous on a fresh re-build. An explantion of when and why to add a FP would be breatly appreciated. And for those wondering why dry nitrous. It is becasue I can run multiple maps and one less solenoid is one less part to break. I have enough injector headroom to add the fuel via the injectors which will provide a more reliable and equall distribution of the extra fuel needed. I will be dyno tuning in a few weeks and will probably add a regulator, but I would like to hear from those in the know. Brand suggestions are also welcome. Thanks Also hoping the walbro can keep up. If not I may just go to an exernal aeromotive.

 

I am no expert but I think that you'll run out of volume with one Walbro before you'll ever need an adjustable fuel pressure regulator. A single 255 LPH pump will deliver enough fuel to support at most between 500-550 WHP before it starts to lean out. If it was me I'd trust the single pump up to about 510 WHP. After that I'd go with a BR intank double-pumper.

With the BR double pumper you probably won't need an adjustable FPR or a larger return line either, IMO. But with just a 50-Trim you'll probably be safe with just a voltage increase to the Walbro such as a thicker gauge hotwire kit or the KenneBell, "Boost-A-Pump" setup. What makes you think that you'll need an adustable FPR anyway?

 

Copied and paste from w website..

"What is a Fuel Pressure Regulator? Why & When do you need one?

What is a Fuel Pressure Regulator?

EFI fuel pressure regulators come in various shapes and sizes but all have the same purpose - to maintain a constant fuel pressure above the intake manifold pressure. The difference in pressure between the fuel rail and intake manifold or differential pressure across the injector should be maintained at a level to suit optimum injector operation.
Why and When do you need to install a Fuel Pressure Regulator?

The installation of an aftermarket fuel pressure regulator allows for the adjustment of fuel pressure to suit larger aftermarket injectors and other engine modifications. They are also necessary to regulate and flow increased volumes of fuel pumped by high flow aftermarket fuel pumps.
Fuel pressure regulator, which works with the fuel pump to maintain a steady pressure relationship between the fuel line side of the injectors and the intake manifold.
Most adjustable regulators are still one to one or close to that, however you can adjust the pressure at idle or full throttle for fine tuning. There is one other type of regulator that is used with aftermarket forced induction. These are rising rate regulators commonly called FMU's (fuel management unit). These regulators increase fuel pressure at a multiplication factor of boost. So instead of messing with complicated computers and injection duty cycles, these systems just increase fuel pressure to add fuel. They go inline down from the factory regulators and only start to add pressure under boost. So when you are off boost, you maintain factory tuning and drivability. Only as you get boost does the FMU begin to increase fuel pressure


Return Flow vs Base Pressure

Ideally a fuel pressure regulator will provide a constant pressure differential across the injectors. Base pressure has been defined as the difference between the fuel rail pressure and the manifold pressure. This is the actual pressure across the injector that affects the amount of fuel flowing through the injector when it is open.

If the base pressure is constant this will aid in tuning by reducing the number of variables the tuner must account for.

The fuel pressure regulator should have the same base pressure at a given setting for all return flow rates through the regulator.


The return flow through a regulator can vary from maximum return flow at idle to approximately 25% of the return flow at full throttle and maximum rpm. For example the test RX7 would return 6L/min at idle and 1.5L/min at 7000 rpm full throttle.


The base pressure is typically tuned at idle when the most fuel is being returned.


If large aftermarket pumps (or high volumes of fuel – eg alcohol based) are used this can mean the regulator is causing a restriction in flow at idle.


This means that when the regulator is being tuned there is an increase is pressure due to the restriction in flow. This is caused by the regulator having to return too much fuel for its design. In effect the base pressure in then being set with a combination of spring pressure and pressure build up due to the flow.


At higher load & rpm there is less fuel being returned through the regulator and the pressure increase due to the restriction in flow will be removed (as the regulator is designed to flow this flow rate) causing a drop in base pressure under these conditions.


This drop is because without the restriction due to too much flow the regulator is only using spring pressure to regulate.


The RX7 tested with twin bosch pumps give a good illustration of this effect with the TREG giving the most stable base pressure and competitors base pressure dropping by up to 4 psi


Bench testing has also confirmed this relationship between regulated pressure and fuel flow."

 

MR, Thank you very much. This was the exact explanation that I was looking for. Now if I need to do a little more homework about that Kenn Bell boost a pump and perhaps a twin pump setup. I am not sure that I believe the marketing hype that beyond 500WHP you will need a dual pumper. I will be somewhere just north of 600 HP on the spray. After reading MR's info, I am convinced that I need a regulator 35 PSI against a 1000cc injector provides a lot of resistance. The bigger the injector the harder it is to open so this is where the FPR will help. Any recomendations for a good one that I could use with the stock fuel rail? I have one of these fuel rail adapters That I could use to mount it a FP gauge.

 

Bump for recomendations for a brand or model.

 

they're all fairly close to being equal. The Aeromotive, Paxton, etc. all share the same design. There are smaller frame ones, but basically the same, like Fuel Labs, etc.

You can't go wrong with Aeromotive or Paxton. I'm running the Fuel Labs regulator as part of a AMS kit, and I'm happy with it, does the job completely and as expected.

 

I don't know about others, but in my case I had to use one in order for my car to run. After my first build which included an AEM EMS and 1000cc injectors, there was an issue where the Walbro pump would prime, pressurize the line, but no fuel would go into the motor. Added the AMS FPR and the car worked fine. AMS has a kit that you can use, basically a fancy bolt on kit for the Fuel Lab regulator.

 

A dual pump system is advantageous north of ~550whp, simply because it relieves some injector duty by maintaining full pressure in the rail.

The injector sees the same resistance with 35 psi in the manifold as it does at idle. No matter whether the manifold pressure is 0, 35, or 55 psi, so long as the fuel pump is adequate, it always has the same ~43psi across it.

The factory FPR is good enough for anything you're going to throw at it. Where a FPR begins to show a shortcoming would be at idle with a large capacity fuel pump.

FYI

 

If you go to a big external Aermotive or Weldon, etc. the problem will be excess fuel volume when driving around while off the spray and at lower boost levels. In this scenario you would probably need an adjusatble FPR as well as a larger I.D. return line to handle the excess volume. Besides your closed loop AFR's would be way funky.

The advantage of a staged double-pumper setup is that you only have the extra fuel volume of the 2nd pump when you really need it. The secondary pump only activates when you're spraying or have reached a certain boost level. So, there is no need for an adjustable FPR or a larger capacity return line.

Also, with a staged dbl. pumper, when you are off boost and not spraying, you are just running on a single Walbro. So, closed loop AFR's would be essentially stocklike.

Additionaly, It is a cool setup as you can rig up an LED to go on when the second pump is triggered via the Hobbes switch circuit. On mine I rigged the LED next to the boost gauge and since the Hobbes is adjustable and the 2nd pump can be adjusted to come on at any predetermined boost level the LED becomes a tuning aid and the pump can can be synchronized to activate when your spray kicks in.

 

Very helpful info. Thanks guys!

 

I'd be willing to bet that one 255HP would be enough in this case. Running 600 hp with a 50 trim and a 100 shot still only requires 500 hp worth of boost. In other words, by using nitrous instead of boost to increase power, you don't make the pump as "small" as you would normally (more pressure makes the pump flow less, obviously). For this same reason strokers can squeeze a little more airflow/HP capacity out of a given pump setup, more airflow with less boost. Nitrous is the same concept.

According to my math, assuming that you are running race fuel with an SG of about .72, target AFR of 11.5:1, and no more than 30 psi on that 50 trim (won't hold more than that), the single rewired 255hp is enough. There isn't much headroom though. Rewiring is mandatory, and I'd start the spray on 20 psi and slowy raise boost watching the WBO2. I wouldn't hesitate to try it, personally.

If you have the means to run two pumps though, by all means go for it. Even when they don't need more fuel, it's rarely wise to discourage people from upgrading just to be safe. I like to experiment though.

 

Sorry off subject and I know you said u r not an expert but a 255 will support up to 650 whp no problem I do have it on my z and its doing fine.

 

You have to be very careful when using HP numbers to rate a fuel pump though. It cost me a motor in my 2g. Fuel pressure, AFR, fuel specific gravity, octane, weight, and a million other things conspire to make rating a pump by HP or track performance impossible.

 

^^ I couldn't agree better

 

At what boost level?

Thanks again everyone. There are a lot of good points being made in this thread. I think since getting to 600 wHP will only be for a matter of seconds on the spray, I will just re-wire the pump and add a FP regulator and maybe a Ken Belle boost a pump. When I start running out of fuel it is time to step down to a smaller jet. I am kinda trying to prove a point by reaching 600 HP on less than 4K in mods which includes a built motor. So that kind of rules out an expensive twin pump. Would love to hear more from Ted B about why you think a stock FPR is fine at any level. Have you done any testing on this? Can it really keep up pressure with 30 or 35 PSI? My concern is the cracking presure of the 1000cc injectors and associated response time.