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Old 03-03-2008, 06:53 PM   #1
Scooby Specialist
Member#: 124060
Join Date: Aug 2006
Location: Bloomfield Michigan
2004 WRX STI

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!

Last edited by DuckStu; 06-05-2008 at 09:01 AM.
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