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kully 560

fuel pressure regulator location

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I pick up a holley fuel pressure regulator 12-804 and was wondering where to install it, is it better on the supply line or the return line for 4 bolt su carbs. I installed it originally on the supply line but have been reading it might be better on the return line as it might help in cooling the fuel , does it really matter ? thanks

Edited by kully 560
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I'm no regulator expert, but I think you need to determine if your regulator is designed for bypass configuration or dead-head configuration. That will tell you which way you need to plumb it.

If it's dead-head, you need to put it in the supply line and (probably) cap off the original return line.

If it's bypass, you need to put it in the return line in place of the stock restriction orifice.

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I will have to check with holley what the regulator is. I did not know the early 260z had a restriction orifice ? do you know where it is located?

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You have not provided enough information to give you an accurate answer.

  1. Why are you considering installing the Holley FPR?
  2. What fuel pump are you running?
  3. Will you be installing a fuel pressure gauge to set the FPR properly?
  4. Are you still using the stock fuel rail? It regulates the pressure with a fixed orifice.

When I used a Holley fuel pump and FPR, I deleted the stock fuel rail and ran braided line to the carburetors. The order of the system was tank to filter to fuel pump to FPR. From the FPR one line went to the carburetors, and one line went to the return line back to the tank.

I fabricated a custom heat shield to block the heat from the headers and ran the fuel lines closer to the carburetors as opposed to the stock fuel rail running near the valve cover. This made it where I didn't need to worry about heat soak.

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25 minutes ago, kully 560 said:

I did not know the early 260z had a restriction orifice ? do you know where it is located?

The restriction orifice is a necked down small-ish hole on the end of the return side of the fuel rail.

Where the return side connects to the rubber hose above the fuel pump:
orifice location.jpg

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 I am was using the fuel rail from my 260 setup with the return line  . I just purchased a refab 240z fuel rail in mint condition and would like to know what is the best way if I needed a pressure regulator or not  . my fuel pump is the carter p60430 rated 2-6 psi. also I check and I though it was a dead head style but wanted to be sure

Edited by kully 560

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The main difference between the 260Z and 240Z fuel rails is the vapor line IIRC. There is a return on the 240Z fuel rail. I would install a fuel pressure gauge before the fuel rail without the FPR and check that. I found many pumps produce less fuel pressure than they advertise. Of course, I also didn't measure the voltage at the pumps to see if that could have caused the lack of pressure.

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what is the vapor line IIrc. my 260z line is insulated and the reason I am changing it it for the nice look .

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 yes I saw the vapor line that runs from the balance tube to the canister. I forgot about that so I guess I will have to keep the canister.  what I have been reading on the net it seems like its more trouble to remove it and better to leave it?  the engine bay would look a lot better with out it !

Edited by kully 560

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I believe the 240 has a similar restriction orifice to the 260.

And about the fuel pressure regulator... I originally said it's dependent on the regulator design and I think I worded that all wrong.  You can run the regulator in either dead-head configuration, or bypass configuration, but it depends on the rest of the system. So let me try again:

If your fuel pump has enough flow capacity to power both carbs and still have flow to spare, then you can run the regulator in bypass mode after the carbs and send the extra fuel (bypass fuel) back to the tank.

If your fuel pump does NOT have enough flow capacity to do the above, then you need to run the regulator in dead-head mode between the pump and the carbs with no return at all. But you'll need to make sure the fuel pump can deal with being dead-headed without overheating. Some pumps cannot deal with running in dead-head mode because they need fuel flow to cool the motor.

Am I just making things worse?  LOL  

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no I do understand what you were saying.  I will take a pressure reading on the supply line and see where the psi is at after I install the 240z rail. if I do need a regulator I will probably use the bypass style on the return line and have the option to dial in. when I installed the new pump I ran a larger wire back there for the voltage drop so the pump will not be starving for power.   the carter pump is 2-6 psi and I would like to have the pressure at 3-3.5 psi .my idea is to clean up the engine bay and get rid of the asbestos covered lines from the 260 fuel rail. the 240 fuel rail does not have the extra line for the vapor canister so I will need to install a vacuum hose from the balance tube to the evap canister. I would love to get rid of the canister for looks but is seems more trouble than what is worth .I read some place maybe over at hybrid z that a person installed a much smaller geo metro canister with great results as it is an updated unit. I will have to look into that down the road some time.

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I don't know if all the holley regulators are the same, but I have been inside one of the little low pressure varieties. I made some internal changes, made some new parts for inside, had some parts left over... That sort of thing. But since it wasn't for my car, I don't remember exactly WHY I did it. It all made sense at the time, but I don't remember the details as to why it was necessary.

My vague notes indicate that I modified it to work on a downstream by-pass configuration. Here's the pictorial summary:

P1130104.JPG

P1130112.JPG

P1130121.JPG

 

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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 .

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 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 by Zed Head

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From the instructions on Holley's website:

image.png

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.

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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 !!

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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.

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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.

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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 by kully 560

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