fuel pressure regulator location

[kully 560]

thanks captain, I did check with holley yesterday and they do not make a low pressure bypass regulator. so with a quick look yesterday on the net I did come up with the aeromotive style that is a low pressure regulator. but I guess I will research that after I install the new fuel rail and check the pressure, it sure would be nice If I do not need it. I am not really sure why the holley 12-804 would not work on the return line unless it is a safety thing.  I guess if it gets stuck closed the bypass style will still pass fuel .

[Zed Head]

 I think that "dead head" and "return" refer to the style of the system, not anything to do with the regulator.  The regulator itself will still bypass overpressure fuel back to the tank, or stop producing flow at a certain pressure value.  So you could put the regulator back at the tank and run a deadhead system, or at the end of the rail.  You could even put the regulator farther down the return line, not right at the engine or carbs.

The regulator will always use whatever pressure the pump can supply though, so flow isn't a huge concern to the regulator.  Any flow problems will probably come from the lines and filters along the way.

The original system uses a blockage in the line, the orifice, because the mechanical pumps have an internal pressure limiting system, with the valves that open up inside stopping pressure buildup.  With an electric pump I think the pressure range that they show is probably the result of voltage swings, which cause motor RPM changes.  Idle voltage gives low flow/pressure, charging voltage gives high.  So with orifice control you'll probably always have pressure swings in the system.  But the needle valve in the float bowl should block that pressure from affecting carb performance. I've not really understood why pressure control is so critical on these carbs.  The floats should rise, the needle valve closes, and the fuel in the carb is at atmospheric pressure, supposedly.   The pressure in the fuel lines can fluctuate but the needle valve should be blocking that from the float bowl.  Maybe the float design is weak.  Maybe it's not the carbs, but the supply lines.  Don't know but you don't see so much discussion about the topic for typical Holleys or Carters or whatever.  They all use floats and needle valves.

Here's a basic article from the global computer file system.

https://www.enginelabs.com/engine-tech/the-answers-deatschwerks-responses-to-your-fuel-system-questions/

Does the location of the fuel pressure regulator matter at all in a return-style system? Does it make a difference if I run the regulator before or after the fuel rails? – Robert C.

A true return-style fuel system places the regulator after the fuel rails. A dead-head fuel system places the regulator before the fuel rails, but on the engine-side of the firewall. As with everything, there are pros and cons to the different systems.

A return-style system provides the most stable fuel pressure and the highest flow potential. This is the most common set-up for aftermarket performance fuel systems and is the best option for builds with really big fuel demands.

Dead-head fuel systems are usually used when the customer has OE rails that have no provisions for a return line, and they don’t want the added expense of aftermarket rails and additional lines and fittings. They also provide a cleaner looking engine bay by eliminating some of the “unnecessary” plumbing.

The only downside with this style versus return-style is they are more susceptible to fuel rail hammer and fuel pressure spikes in rapid transitions from high to low fuel demand. If I were building a 1,000-horsepower or bigger system, I would go with full return-style. In anything else, it doesn’t really matter.

Edited January 6, 2021 by Zed Head

[SteveJ]

From the instructions on Holley's website:

I used the configuration in Figure 2 for the 12-804 FPR, but again, I did not use a stock 260Z or 240Z fuel rail.

[kully 560]

well Zed Head, when I spoke to holley tech yesterday I was told it is a different regulator!  the 12-804 is a dead head type like in STEVESJ diagram #1. they do not make a 1-4 psi bypass regulator .  STEVESJ diagram # 3 is the way it should be setup when a z car has a return fuel line. [note Holley bypass regulator] what the hell is the difference between the bypass and the dead head style I do not know.  Holley tech recommends not using the dead head on the return line only bypass style. so right now I am just improving the looks of the engine bay with a nice coated fuel rail and not being covered in asbestos like my 260 rail . so when the new rail gets installed I will put the pressure gauge on the supply line with a tee and take a reading at different rpms and see if it changes. if it stays steady at around 3- 3.5 lbs then there is no need for the regulator. if it does not, then I would like to have the ability to dial in a perfect pressure setting. now in this day and age we can do that on a 45-50 year old system. does it matter on a performance aspect probably not . but being stuck home with the covid and crap all around I need projects to keep from going out of my mind .  this helps and the z will like !!

[Zed Head]

I think that you just need to know how the regulator works.  The mechanism of pressure control.  You can use a bypass regulator with three ports and make it do whatever you want, deadhead or bypass the carbs.  That's how Aeromotive does theirs.

I don't really understand how the Figure 1 regulator does its thing.  I'll have to dig in to it.  I do know though the pump will put out maximum pressure in that type of system, so if you have a high flow/high pressure pump in a Figure 1 setting, it's going to be working hard but pushing nowhere.  Probably the noisiest possible configuration.

I think these things are why the car manufacturers control the pump power with the ECU now.  They lower voltage at low need, and raise it at high.  Flow control.

[w3wilkes]

Just a couple of comments on this. When the dealership put an electric pump in my 73 they put a fuel pressure regulator in the line between the front fuel filter and the mech fuel pump (which was left in). The fuel rail still had the restrictor at the end of the fuel rail back to the tank. Four years ago (2017) in my 71 I removed the mech pump, did the low pressure K&N pump from MSA back at the tank and have no regulator other than the restrictor at the end of the fuel rail back to the tank. It has been completely trouble free. I would consider a different low pressure pump that's quiet, the K&N does make some noise.

[kully 560]

well I just finished installing the recondition 240 fuel rail and removed the 260 one with the asbestos . I am not going to install a fuel pressure regulator as with the carter p60430 pump the fuel pressure is at  3.95 psi with the gauge installed at the start of the new fuel rail.  I just ran a vacuum line from the balance tube to the carbon canister to solve that problem. 

Edited January 20, 2021 by kully 560

[Jeff Berk]

I'm working on modifying my fuel delivery and need a reality check if anyone wants to comment. My current system has fuel going from no return to a return to try and control fuel pressure and prevent the fuel from becoming too hot while waiting in line between autocross runs.

electric pump ==> mechanical pump (MP unable to keep up with the demand) ==> fuel pressure regulator (no return port) ==> "T" fitting ==> SU (4-screw)

I was planning on switching to:

electric pump ==> mechanical pump  ==> fuel rail ==> SU carburetors front

                                                                                 ==> SU carburetor rear 

                                                                                 ==> Fuel pressure regulator ==> return line ==> Fuel Tank

fuel system.pdf