fuel pressure regulator location

[kully 560]

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 January 5, 2021 by kully 560

[Captain Obvious]

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.

[kully 560]

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?

[SteveJ]

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.

[Captain Obvious]

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:

[kully 560]

 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 January 5, 2021 by kully 560

[SteveJ]

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.

[kully 560]

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

[kully 560]

 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 January 5, 2021 by kully 560

[Captain Obvious]

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?    

[kully 560]

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.

[Captain Obvious]

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: