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Old 03-03-2008, 06:53 PM   #1
DuckStu
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Default Fuel line routing. (With pictures and arrows).

Ok, so I have been wanting to parallel my fuel rails and have long wondered what is involved,..how the stock stuff is routed etc. Never found a good picture, so I thought I'd take some pictures while fumbling my way through it. I'm down in there anyway doing a new turbo (FP 20-G SL2, with 3" compressor inlet), a 3" turbo inlet tube and a set of JDM TGV deletes.

Not sure if paralleling the fuel rails is necessary. The jury seems to be out on this one. Some say they have tested and found a pressure drop in the metal lines alone (I think it was an engineer that worked for Perrin that said that, although I am told Perrin doesn't have any engineers working for them, and maybe never has),...others say that the fuel pressure drops by the time it gets to the last cylinder in the loop (cyl #3, passanger side rear) and this is why cylinder 3 is prone to failure. Others say the stock setup is fine to 500 wheel hp. I don't have the answer, but for about $35,... it's cheap insurance.

Here's a birds eye view of what is going on down in there. Looking at it from the drivers seat, (more like if you were sitting on the windshield looking down).

There are 3 tubes that enter the manifold area on the left (drivers' side). The top one is fuel supply, the second one down is the return, and the smaller one at the bottom (not visable here for some reason) is a vent line that I think goes to the charcoal canister under the passanger side rear of the car.

First the raw pic. (These from my 2004 STI).



And one with circles and arrows on the back of each one explaining what it was to be used as evidence against me. (Please excuse the Arlo Guthrie reference).




The parts list is pretty easy;

*Two 1/4" NPT brass Tees, (I got mine at Harbor Freight for about $3.00 each, but Home Depot, Lowes etc have them too for about the same price).
*Six 5/16" brass hose barbs ($1.36 each at local hardware store)
*A dozen 5/16" fuel injection hose clamps. (About $12.00 at auto parts store.)
*And roughly 7 feet of 5/16" fuel injection hose. (About $1.29 a foot, or $9.00)
Total cost about $35.00

So here is the next step.

This time looking from the front of the car,...(so you'll have to turn yourself around). I have the JDM intake risers (TGV deletes) temporarilly installed. I ran two 5/16" fuel injection hoses between the 2 rails. I don't know that it matters which goes to which. I chose to have the feeds going in the front, which is the way the factory setup was.


Next,...I cut the lines and inserted the brass Tees with 5/16" hose barbs on them. Make sure to use fuel injection clamps. I found that Autozone didn't carry F.I. clamps at all,..and the other stores only had one pack of 4 each. So if you're going to do the project,...think ahead and buy a pack each time you go to the autoparts store, so you'll have them when you need them.

Here's the Tees installed.


Next is to run a couple of supply hoses and install the fuel pressure regulator. Space is getting tight, so I chose to wait and install the regulator on top of the intake manifold.

Ok, so here's the intake re-installed. You can see the supply and return lines comming out of the intake at the right.

NOTE,..IMPORTANT,..CRITICAL EVEN. The most important connection in the entire car has to be this little vacuum line (labeled "reference hose") going from the Boost Referenced Fuel Pressure Regulator to the intake. If you don't know what this does,..I'll explain. Fuel flows out of the injectors because it is at 40 psi (let's say for argument sake),...and there is no pressure in the intake (when at 0 boost). But at 20 psi of boost,..the pressure difference drops in half,..and so too will the amount of fuel comming out of the injectors. Can you say KABOOM? So this regulator is of the "Boost Referenced" variety,..meaning as boost pressure rises,..so too does the fuel pressure. With this type of regulator,..at 20 psi of boost, we will have 60 psi of fuel pressure instead of 40. (It may be more like 43 psi base,..but I'm generalizing here).

I cannot stress enough how important that this line not even come off or get cut from abrasion etc. So much so that I usually install a new line and then JB Weld and double zip-tie them on.

Either of the top-mount intercooler bracket bolts made perfect regulator mounting points,..so voila! Done!
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Last edited by DuckStu; 06-05-2008 at 09:01 AM.
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Old 03-03-2008, 09:18 PM   #2
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Nice detailed pic with arrows, this should be a sticky.
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Old 04-10-2008, 07:30 PM   #3
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Thanks for the awesome write up


Quick question, did you need a retune? Any trouble getting to a tuner?
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Old 04-21-2008, 06:46 AM   #4
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I just though I'd throw in that this mod doesn't work with stock wrx fuel rails The FPR can't be relocated since it's attached to the passenger side fuel rail. Therefore, you need some strange FPR adapters to move it. You would need a male FPR adapter to hook up to the fuel rail and a female adapter to hook up the FPR. At that point, it's probably a better idea to purchase fuel rails.
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Old 04-29-2008, 01:59 PM   #5
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--you cut the bracket that attached the FPR. check the APS turbo inlet install it relocates the FPR to the tranny case.
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Old 04-29-2008, 03:02 PM   #6
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Quote:
Originally Posted by Steel06STI View Post
--you cut the bracket that attached the FPR. check the APS turbo inlet install it relocates the FPR to the tranny case.
thanks for the info, but the sti has different fuel rails. The stock wrx rails, the FPR is welded to the stock fuel rail. So to move it, you would need to cut the back end off the fuel rail off... not something I want to do.

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Old 05-18-2008, 12:53 AM   #7
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Nice write-up. I am going to pick up the parts to do this tomorrow. I was thinking of doing rails later on but after experiencing how big of a PITA it is to remove the manifold, I will be making time to do this before reassembly.
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Old 05-20-2008, 01:48 PM   #8
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Is it not ok to use regular style hose clamps. They should be able to be tightened tight enough to seal and not leak right?
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Old 05-20-2008, 01:57 PM   #9
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^ yes, must use special fuel injector hose clamps fitted to the right size of the line.
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Old 05-24-2008, 09:34 AM   #10
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I was able to reuse the clamps that came off of my stock lines. I am worried though because everything seems to be really tight clearance. I wrapped wire loom around a few potential problem areas but i was just curious as to if anyone has had any problems with this as of yet? I even have 8mm Grimmspeed spacers and there is still little to no clearence.
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Old 05-24-2008, 09:42 AM   #11
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incase people are wondering.. YES YOU CAN DO THIS ON A WRX.

just pick up an STi FPR
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Old 06-05-2008, 06:59 PM   #12
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thanks for this post was about to spend 300 on perrin rails

looks farly easy to do and cheap
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Old 06-06-2008, 12:03 AM   #13
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Quote:
Originally Posted by sidewayz View Post
incase people are wondering.. YES YOU CAN DO THIS ON A WRX.

just pick up an STi FPR
You would need that as well as a honda FPR adapter fitting
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Old 06-06-2008, 01:41 AM   #14
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Quote:
Originally Posted by EROC263 View Post
I was able to reuse the clamps that came off of my stock lines. I am worried though because everything seems to be really tight clearance. I wrapped wire loom around a few potential problem areas but i was just curious as to if anyone has had any problems with this as of yet? I even have 8mm Grimmspeed spacers and there is still little to no clearence.
Be very aware of how you route the fuel lines as you don't want any of them kinking or pinched. I had done the 3" hard inlet pipe install with 8mm phenolic spacers and had to reroute the fuel lines. Things will move around especially when the engine torque movement on the engine mounts, even with the pitch stop. I believe that one of the lines got pinched and caused a 20% reduction in fuel output to one of the rails which eventually caused detonation to spin a rod bearing. I purchased the APS fuel rail kit with the stiffer stainless lines now so it already comes in the parallel configuration.
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Old 06-06-2008, 09:16 AM   #15
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Quote:
Originally Posted by methaddict View Post
Be very aware of how you route the fuel lines as you don't want any of them kinking or pinched. I had done the 3" hard inlet pipe install with 8mm phenolic spacers and had to reroute the fuel lines. Things will move around especially when the engine torque movement on the engine mounts, even with the pitch stop. I believe that one of the lines got pinched and caused a 20% reduction in fuel output to one of the rails which eventually caused detonation to spin a rod bearing. I purchased the APS fuel rail kit with the stiffer stainless lines now so it already comes in the parallel configuration.

The lines are in-between the block and the intake manifold. Both of which move together as a unit. There shouldn't be any pinching or rubbing going on once the manifold is on.

I left some slack in my lines,..and they run towards the rear where there is more space. Right under the manifold is impossibly tight. Under the throttle body and intercooler,..there's lots of space.

Just be carefull when reinstalling the intake manifold that the lines aren;t getting pinched.

And there's no reason the intake and TGV's have to go on together. In stock form they do because the fuel crossover lines bolt to the bottom of the intake and because the lines poke out through the drivers side of the intake,...and it takes some doing to get them in our out. But once you eliminate those metal lines,..the manifold can go on seperately. This is SUPER nice for doing a metal 3" turbo inlet. You can get everything sorted,..then just drop the intake on top.
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Old 07-05-2008, 11:16 AM   #16
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question

what did u do with that 3rd line?
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Old 07-12-2008, 10:41 AM   #17
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Why would the fuel after step 5 exit into a fuel pressure regulator if it is being returned to the tank?
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Old 07-12-2008, 10:57 AM   #18
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Quote:
Originally Posted by srREXed View Post
Why would the fuel after step 5 exit into a fuel pressure regulator if it is being returned to the tank?

The regulator is what regulates fuel pressure. It acts as a restriction,... and restriction to flow is what causes pressure.

If it were before the injectors,..there wouldn't be much of any pressure AT the injectors. So the fuel goes from the pump to the rails, past the injectors..then to a variable restriction (regulator). And the leftover goes back to the tank.
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Old 07-12-2008, 11:27 AM   #19
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Quote:
Originally Posted by DuckStu View Post
The regulator is what regulates fuel pressure. It acts as a restriction,... and restriction to flow is what causes pressure.

If it were before the injectors,..there wouldn't be much of any pressure AT the injectors. So the fuel goes from the pump to the rails, past the injectors..then to a variable restriction (regulator). And the leftover goes back to the tank.
You arent understanding me. (i build motors) He shows the flow opposite of what it really is in the diagram. He shows the fuel flow going outbound to the tank from the fpr. The fpr is the component that gets the fuel 1st, not last. It regulates the fuel coming in so when it exits the regulator is has X amount of pressure, then to the rails and so on... Did he do that by accident? I hope the setup he put on the car didnt follow that flow chart. I just noticed that by accident.
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Old 07-14-2008, 09:20 AM   #20
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Every EFI setup that I've seen and worked on has the FPR at the return line, not the feed.


Quote:
Originally Posted by srREXed View Post
The fpr is the component that gets the fuel 1st, not last.
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Old 07-14-2008, 01:11 PM   #21
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Quote:
Originally Posted by srREXed View Post
You arent understanding me. (i build motors) He shows the flow opposite of what it really is in the diagram. He shows the fuel flow going outbound to the tank from the fpr. The fpr is the component that gets the fuel 1st, not last. It regulates the fuel coming in so when it exits the regulator is has X amount of pressure, then to the rails and so on... Did he do that by accident? I hope the setup he put on the car didnt follow that flow chart. I just noticed that by accident.
No, you just don't get it, morAn.

I hope you only build carburated motors

Last edited by fujiillin; 07-14-2008 at 01:55 PM.
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Old 07-14-2008, 01:37 PM   #22
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Just have to ask...but what would be the point/advantage of doing this?
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Old 07-14-2008, 02:21 PM   #23
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FPR is AFTER the injectors/rails. AFTER.

The pump flows fuel from the tank to the FPR. The pressure is maintained from the pump to the FPR, in between which sit the injectors. Any excess pressure over what the FPR is set for is relieved into the return line which goes back to the tank.

I just wanted to reclarify what has already been said.
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Old 07-14-2008, 09:41 PM   #24
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Quote:
Originally Posted by srREXed View Post
You arent understanding me. (i build motors) He shows the flow opposite of what it really is in the diagram. He shows the fuel flow going outbound to the tank from the fpr. The fpr is the component that gets the fuel 1st, not last. It regulates the fuel coming in so when it exits the regulator is has X amount of pressure, then to the rails and so on... Did he do that by accident? I hope the setup he put on the car didnt follow that flow chart. I just noticed that by accident.
Ha ha ha... Nice. Well there is no need for the name calling. Its quite interesting to see that there are actually educated people on this forum. This is only a test of the national broadcasting station. I repeat, this is only a test... I can post pics of my fuel system if you want... You all will be quite intrigued. LMK if you want pictures.
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Old 07-14-2008, 09:44 PM   #25
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Quote:
Originally Posted by wcbjr View Post
FPR is AFTER the injectors/rails. AFTER.

The pump flows fuel from the tank to the FPR. The pressure is maintained from the pump to the FPR, in between which sit the injectors. Any excess pressure over what the FPR is set for is relieved into the return line which goes back to the tank.

I just wanted to reclarify what has already been said.
Reg gets fuel after rails before tank return to clarify. Sorry for confusing you all. I just finished some fuel system removal on an sti and figured to mess around on the forum a bit. didnt mean to cause a mess. I have sti fuel parts for sale in the private fs forum if anybody would like some low mileage stuff.
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