Was talking to a buddy of mine and discussing regulator position and he says it should be on the return side and I said feed side. It's a holley 12-886 regulator. Documentation I've read says it could go either way. What are y'alls thoughts on the placement?
CK5
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Where to place regulator
- Thread starter centexk5
- Start date
Return side is what @folkenheath advised me to do. Been working fine. IIRC, the reasoning is that with the regulator on the feed you have deadheaded fuel in the rails. Putting it on the return keeps fuel flowing thru the rails and minimizes heat buildup in the fuel.
Yeah, the short answer may be "both", as-in the fuel pump to regulator, which then feeds the rail and the return line. The early factory setups had it on the outlet of the fuel rail. By asking which one, you've established that you do have a return line. This is an EFI regulator (high pressure), so it would help if you told us the application.
You have a few options....
1 -The most optimum setup is to split the fuel line with a Y, go into each rail, then use the regulator as a "T" for the rails to flow back into. You then return to the tank. This keeps equal pressure on both rails and allows fuel to flow and not dead head any fuel or air. This is how I plumb my own systems. This pic I found from Aeromotive when I was looking for an illustration of how I plumb it.
2 - Many people run the fuel through one rail, then the other, then to the regulator, which works fine in many applications, although higher HP applications can make it so the one rail robs the other and you can end up with uneven fuel pressure in the rails. This also allows the fuel to constantly move, just like the pre-split Y method, and use the entire fuel tank as a reservoir for fuel temp changes. This will still purge air from the rails automatically as well.
3 - The least desirable is to dead head the fuel rails by going directly through the regulator to return back to the tank, and having a single supply from the regulator to the fuel rails, so the only fuel that's "flowing" is through the regulator and return line. Although in many mild performance applications that works without problems. But it's not as quick to prime the system and purge air from the rails, and it also won't be as fast of response to maintain pressure in higher HP applications, because the fuel will need to start moving rapidly to respond in a pressure drop, and if the fuel is already flowing through the rails constantly it's faster for it to be redirected through the injectors. This method also lets the fuel in the rails continue to get warmer as you just cruise around, with barely any fresh fuel flowing into the rails. The factory does this quite often because it its less expensive to plumb, especially if you put the regulator closer to the tank so the return line is very short, or sometimes never leaves the tank.
The most important thing is you have the correct fuel pump and regulator, which I know you do, so whatever works for you to plumb will probably work OK, I'm just pointing out some of the pros and cons.
l like to use the Fragola Y fitttings, and then a straight hose end in, and two 30 deg hose ends out, and you end up with essentially 1 - 2 split with parallel plumbing to the rails. Then whatever hose ends you need to go into the rails and out to the regulator.
1 -The most optimum setup is to split the fuel line with a Y, go into each rail, then use the regulator as a "T" for the rails to flow back into. You then return to the tank. This keeps equal pressure on both rails and allows fuel to flow and not dead head any fuel or air. This is how I plumb my own systems. This pic I found from Aeromotive when I was looking for an illustration of how I plumb it.
2 - Many people run the fuel through one rail, then the other, then to the regulator, which works fine in many applications, although higher HP applications can make it so the one rail robs the other and you can end up with uneven fuel pressure in the rails. This also allows the fuel to constantly move, just like the pre-split Y method, and use the entire fuel tank as a reservoir for fuel temp changes. This will still purge air from the rails automatically as well.
3 - The least desirable is to dead head the fuel rails by going directly through the regulator to return back to the tank, and having a single supply from the regulator to the fuel rails, so the only fuel that's "flowing" is through the regulator and return line. Although in many mild performance applications that works without problems. But it's not as quick to prime the system and purge air from the rails, and it also won't be as fast of response to maintain pressure in higher HP applications, because the fuel will need to start moving rapidly to respond in a pressure drop, and if the fuel is already flowing through the rails constantly it's faster for it to be redirected through the injectors. This method also lets the fuel in the rails continue to get warmer as you just cruise around, with barely any fresh fuel flowing into the rails. The factory does this quite often because it its less expensive to plumb, especially if you put the regulator closer to the tank so the return line is very short, or sometimes never leaves the tank.
The most important thing is you have the correct fuel pump and regulator, which I know you do, so whatever works for you to plumb will probably work OK, I'm just pointing out some of the pros and cons.
l like to use the Fragola Y fitttings, and then a straight hose end in, and two 30 deg hose ends out, and you end up with essentially 1 - 2 split with parallel plumbing to the rails. Then whatever hose ends you need to go into the rails and out to the regulator.
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Seems like either or but return is preferred. Makes no difference to me. Return would be slightly easier to plumb. With a little luck I should be able to start making lines this weekend.
Now I’m curious, isn’t the regulator supposed to regulate how much fuel gets to a certain area not how much leaves it? I admit modern injection isn’t something I’m hip to, but it seems like regulating the return only regulates how much fuel goes back to the tank?
Second this question
The name of it is "pressure regulator", so of course it regulates the pressure, not the flow. So as you say, it determines how much fuel returns to the tank. This is what you want because the pump is not any kind of smart device. It is just spinning and the flow/pressure turn out based on the overall system restriction, consumption, etc. The engine tuning is based on having a certain amount of pressure behind the injector, i.e. for a certain pulse width you get a certain amount of fuel.
By definition of having a pressure regulator, the pump supplies a set pressure. Flow/supply is basically irrelevant until the pump can't keep up with the operating conditions. No matter where you put the regulator, it is a restriction by definition, unless you are exceeding the limits of the pump.
Holley Terminator with two fuel rails.
Makes sense….my thinking is if I need 50 psi at the fuel rail and my pump is capable of putting out 100 psi don’t I need to regulate that to 50 psi before the rail?
If I’m understanding @Bent77 correctly I’d send the 100 to the rail the engine uses what it needs and I regulate it down after that, but what I don’t get is if you send 100 to the rail and the engine only uses what it needs won’t the rest just return to the tank? Why regulate after the fact?
If I’m understanding @Bent77 correctly I’d send the 100 to the rail the engine uses what it needs and I regulate it down after that, but what I don’t get is if you send 100 to the rail and the engine only uses what it needs won’t the rest just return to the tank? Why regulate after the fact?
Nope. Putting the regulator after with still maintain that pressure without restricting the flow prior to getting to the “load” as it were. That leaves the load in the controlled pressure and flow side, and the output side is essentially what you don’t need
I numbered the methods in the order I would recommend them. The first two are definitely better than the 3rd option, they don't dead head the rail. To answer your original questions, if you can, I would put the regulator after the rail.
He has a MPFI Holley Terminator X Max system with 2 fuel rails, yes.
You are correct, however, since the bypass regulator won't let the pressure rise above the set point (because it bypasses the excess fuel back to the tank), anywhere in the system won't rise above the set point. You are probably thinking of a dead head regulator (not return style) for a mechanical fuel pump, those reduce the pressure with a spring loaded restriction before the carburetor, and can't limit flow even if the pump has higher flow. The pressure before the regulator on those type can be higher because the excess fuel has no where to go. You can't use those with most electric pumps, as the pump can burn up if the fuel can't flow.
I agree, he is just saying if you put the regulator after the fuel rail, then the restriction is not between the pump and the injector, you get full flow straight to the fuel rails.
I should add, with a bypass style regulator the restriction is not between the pump and injector in any of the methods if it is plumbed right, because the restriction is only before the return, which is low pressure after that. And even dead headed rails the fuel can flow through the bypass regulator to the rails without going through the restriction. With the old dead head style mechanical pump regulators, the restriction is before the carb, which if it's too small can starve the carb of fuel.
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Finally got time to sit in the engine bay and think about this. Here is my current thought.
Feed line to a y-block mounted behind the distributor, then run the lines between the intake and valve covers to fittings in the front of the rails for feed, and then from the back of the rails to the regulator mounted above the distributor, and then return line down the passenger frame rail. Some mock up makes it look like it’ll fit.
Feed line to a y-block mounted behind the distributor, then run the lines between the intake and valve covers to fittings in the front of the rails for feed, and then from the back of the rails to the regulator mounted above the distributor, and then return line down the passenger frame rail. Some mock up makes it look like it’ll fit.
Your idea should work fine. If it were me, I'd hate to buy the additional fuel line that is duplicating the path of the fuel rails. You could put the regulator at the front of the engine. I have mine there mounted with a bracket to the intake.
If you do run lines up to the front of the fuel rails, you should consider putting them to the inside of the fuel rails so they don't get in the way of pulling the valve covers.
If you do run lines up to the front of the fuel rails, you should consider putting them to the inside of the fuel rails so they don't get in the way of pulling the valve covers.
If I may, I’d like to slightly hijack this one. 
So I know the discussion has mostly been for EFI applications, but what’s the general consensus for a carb’d application?
In my case, I’m running a factory fuel tank and lines, but my vortec block does not have the provisions for a block mounted pump for my quadrajet. I’m going to run a lower psi frame mounted pump therefor I’d like to run a pressure regulator. Would this be an application where you run it on the feed side as to not over pressurize the carb?
So I know the discussion has mostly been for EFI applications, but what’s the general consensus for a carb’d application?
In my case, I’m running a factory fuel tank and lines, but my vortec block does not have the provisions for a block mounted pump for my quadrajet. I’m going to run a lower psi frame mounted pump therefor I’d like to run a pressure regulator. Would this be an application where you run it on the feed side as to not over pressurize the carb?
Yeah, you need to kill the pressure before the carb. Otherwise the fuel pressure can unseat the needle valve.
Ah good point, I wasn’t thinking about that at all.
You got a picture of that bracket? I was struggling trying to picture one in my head yesterday. Ideally that’s where I want to mount the regulator. Makes life a lot easier. Then I could run the return in the air gap space on the manifold and keep everything nice and neat.
