Fuel pressure regulator goes on supply or return?
Thread Starter
TECH Enthusiast
Joined: Jun 2011
Posts: 589
Likes: 2
Fuel pressure regulator goes on supply or return? I ordered a fuel pressure regulator and fittings and lines to plumb my fuel system but I believe they sent me -8 fittings to connect the regulator which would mean it would go on supply side rather then return because I have -6 return line. I thought regulators were supposed to go on the return side. Can you put them on the supply side?
All factory returnless systems have them on the supply side. The regulator is actually in the tank right next to the fuel pump, so it returns fuel to the tank, but since its in the tank you dont see it, hence returnless.
Typical return style systems have the regulator after the rail.
Typical return style systems have the regulator after the rail.
How would you be able to regulate the pressure if the feed (from the tank) went straight to the rails? would they not be subject what ever PSI the pump was putting out? Ive always set mine up the way i described
Last edited by oscs; Apr 22, 2014 at 01:01 PM.
It keeps the rails at pressure and bleeds off anything over that pressure. It is a common way of hooking up a regulator. Look it up on Google, I am sure you will see tons of diagrams and discussion.
Trending Topics
Thread Starter
TECH Enthusiast
Joined: Jun 2011
Posts: 589
Likes: 2
So you run yours feed line going to regulator, then feed line coming out of regulator. Which then goes to rails that have a cross over and then a return coming out of one rail correct?
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
Gas Monkey Built a 6-Wheel Ferrari Testarossa With a Corvette LT4 Engine
Verdad Gallardo
7 Most Reliable High-Performance Engines GM Has Ever Built
Verdad Gallardo
Amazing '71 Camaro Restomod Is Modern Muscle Car Under the Skin
Verdad Gallardo
6 Common C5 Corvette Failures and What's Involved In Repairing Them
Pouria Savadkouei
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Verdad Gallardo
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo
Coachbuilt N2A Anteros Is an LS2-Powered C6 Corvette In Italian Clothes
Verdad Gallardo 
Last edited by oscs; Apr 22, 2014 at 01:39 PM.
I see how this work now, guess i had a brain fart. I like my way becuase i feel like it would keep a more consistent FP rate with them dead ending at the rails. But hey im wrong all the time and open to options.
Thread Starter
TECH Enthusiast
Joined: Jun 2011
Posts: 589
Likes: 2
If you are looking at the regulator The line on the left is -10 feed the line on the right is -10 feed as well, it hits the Y block and splits to (2) -8 lines. Those lines are fed to each rail constantly maintaining your desired FP. The line on the bottom of the regulator is -8 return and goes strait to the fuel tank.
It is basically like a returnless system, just the regulator is in the engine compartment unlike the vet. A traditional returnless though has a crossover rather than dead ends at both rails.
I have -8an from my pumps to my passenger side rail. -8an from passenger to driver side rail. then i exit the back side of the driver side rail with -8an and go to my regulator. I capped the second port on the regulator and run a -6an return line from the bottom of the regulator back to the tank.
Thread Starter
TECH Enthusiast
Joined: Jun 2011
Posts: 589
Likes: 2
Your way of doing it can be dangerous. Aftermarket fuel pressure regulators should be hooked up after the rails. Meaning pumps to rails then to regulator/return. Its dangerous because you could realistically consume all of the fuel before it reaches the back of the rail. With the regulator after the rails, it will just return any unused fuel to the tank. You are right when you say the pumps will just pump what they can but you might be consuming almost all of it at full load. Your setup may have trouble keeping those rear injectors full of fuel.
I have -8an from my pumps to my passenger side rail. -8an from passenger to driver side rail. then i exit the back side of the driver side rail with -8an and go to my regulator. I capped the second port on the regulator and run a -6an return line from the bottom of the regulator back to the tank.
I have -8an from my pumps to my passenger side rail. -8an from passenger to driver side rail. then i exit the back side of the driver side rail with -8an and go to my regulator. I capped the second port on the regulator and run a -6an return line from the bottom of the regulator back to the tank.
Your way of doing it can be dangerous. Aftermarket fuel pressure regulators should be hooked up after the rails. Meaning pumps to rails then to regulator/return. Its dangerous because you could realistically consume all of the fuel before it reaches the back of the rail. With the regulator after the rails, it will just return any unused fuel to the tank. You are right when you say the pumps will just pump what they can but you might be consuming almost all of it at full load. Your setup may have trouble keeping those rear injectors full of fuel.
I have -8an from my pumps to my passenger side rail. -8an from passenger to driver side rail. then i exit the back side of the driver side rail with -8an and go to my regulator. I capped the second port on the regulator and run a -6an return line from the bottom of the regulator back to the tank.
I have -8an from my pumps to my passenger side rail. -8an from passenger to driver side rail. then i exit the back side of the driver side rail with -8an and go to my regulator. I capped the second port on the regulator and run a -6an return line from the bottom of the regulator back to the tank.
thats funny becuase this is exactly what i was trying NOT to do. Ill give it some more thought.
9 Second Club
Joined: Nov 2003
Posts: 13,616
Likes: 185
From: Norn Iron
Flowing the main feed line into the regulator and then the rails would be the least desirable option.
Flowing the main feed line, parallel into the rails and then into the regulator is the most favourable option
But really there are multiple ways to configure it.
And whilst what Ryan says is true to a degree, if it was to happen you would see fuel pressure dropping ( of course you'd need to be logging it to see it )
@oscs.
If you insist in retaining yours the way you have, I would at least tee the regulator off that main feed line. That way supply fuel isnt having to pass through the regulator body which could be a restriction.
But really you would be best splitting that main feed into two lines, one for each rail.
Then exit the rails at the front and back into the regulator, then return as normal.
Edit...hard to see what way it is actually plumbed ? Have you split from the main feed to feed each rail ?
Flowing the main feed line, parallel into the rails and then into the regulator is the most favourable option
But really there are multiple ways to configure it.
And whilst what Ryan says is true to a degree, if it was to happen you would see fuel pressure dropping ( of course you'd need to be logging it to see it )
@oscs.
If you insist in retaining yours the way you have, I would at least tee the regulator off that main feed line. That way supply fuel isnt having to pass through the regulator body which could be a restriction.
But really you would be best splitting that main feed into two lines, one for each rail.
Then exit the rails at the front and back into the regulator, then return as normal.
Edit...hard to see what way it is actually plumbed ? Have you split from the main feed to feed each rail ?
Flowing the main feed line into the regulator and then the rails would be the least desirable option.
Flowing the main feed line, parallel into the rails and then into the regulator is the most favourable option
But really there are multiple ways to configure it.
And whilst what Ryan says is true to a degree, if it was to happen you would see fuel pressure dropping ( of course you'd need to be logging it to see it )
@oscs.
If you insist in retaining yours the way you have, I would at least tee the regulator off that main feed line. That way supply fuel isnt having to pass through the regulator body which could be a restriction.
But really you would be best splitting that main feed into two lines, one for each rail.
Then exit the rails at the front and back into the regulator, then return as normal.
Flowing the main feed line, parallel into the rails and then into the regulator is the most favourable option
But really there are multiple ways to configure it.
And whilst what Ryan says is true to a degree, if it was to happen you would see fuel pressure dropping ( of course you'd need to be logging it to see it )
@oscs.
If you insist in retaining yours the way you have, I would at least tee the regulator off that main feed line. That way supply fuel isnt having to pass through the regulator body which could be a restriction.
But really you would be best splitting that main feed into two lines, one for each rail.
Then exit the rails at the front and back into the regulator, then return as normal.
I agree, the last way of doing it actually allows me to use what i already have or most of it for that matter.
Mine has a -10 feed with a Y going into -8 fittings in each rail, then two seperate return lines coming out of the rail and into the regulator. I have heard is is important to try to make sure both of the lines coming out of the rail are equal length. Not sure how true this is, but I did it anyways, haha. From the regulator I have a single -10 going back to the tank.
I used the larger line due to using E85. I have had bad experiences using too small of a return on E85 and it becoming a restriction when using very large pumps. Actually had a car that at idle would not go lower than 55 psi fuel pressure, but then as the motor started actually using fuel it would drop down to 45psi before climbing back up with boost. Until I figured out what was happening I was having a HELL of a time tuning the car, lol.
I used the larger line due to using E85. I have had bad experiences using too small of a return on E85 and it becoming a restriction when using very large pumps. Actually had a car that at idle would not go lower than 55 psi fuel pressure, but then as the motor started actually using fuel it would drop down to 45psi before climbing back up with boost. Until I figured out what was happening I was having a HELL of a time tuning the car, lol.