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DIY split fuel rails Reply #3


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I dont know what im doing.lol. I know they stop the fourth cylinder from leaning out . My car is a v2 sti ra. its gotta fifth injector so will that be an issue?

As far as regulators etc i dont know where to start so i need suggestions and advice from people who have done it before so i can get exactly what i need and get straighht into it.

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lol right..

two options for doing it

#1 use two right hand fuel rails, as they have (factory) fuel regs attached to them. You then run your normal reg in its usual position, and the other right rail on the left side.

#2 Use an after market fuel regulator and you can run two left rails, and the fuel reg will take inputs from both rails and do it for you.

Things you will need either way,

  • 1x set of manifold gaskets
  • 10+ fuel hose clamps
  • 1m of Vac hose
  • length of marine grade fuel hose (i got 4m for option #1)
  • 2 x brass tees if doing option #1 that fit the fuel hose
  • aftermarket risiing rate fuel regulator (if doing option #2)
  • a left rail for option #2, a right rail with fuel reg attached for option #1
  • A vac hose size tee join

NoteWith version 1/2 you can get premade tees that bolt to the rails to connect fuel hose to so depends you made need those or you can just cut the standard fuel lines and create the flared ends yourself (if you hvae the tool).

I think (please verify) that you dont have to worry about injector number 5.

So decide the way you want to go... I think #1 is a bit cheaper as you dont need to buy the aftermarket fuel reg. Althought the piping is probably a little harder to run for option #1.

For #1

Cut the four peices of fuel line from the Fuel rails to the Brass tees the same length.

you plumb the fuel reg lines together then back the the main fuel return line up past the fuel filter.

you plumb the fuel in line into the line you will have removed off the fuel filter.

The old metal fuel lines under the manifold can be removed.

You dont need to plumb the fuel breather back in.

It is more difficult to route option #1 under the manifold on the earlier version rex's and RS's

You need the vac hose to plumb the new reg onto the manifold somewhere.

updates and additions welcome

Heres the pics for #1

manifoldup.jpg

manifolddown.jpg

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nice. so really all i need is a left hand side rail?

i can get all the other stuff cheap as but the main thing is just the rail itself?

roughly how long did this take you?

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yes another right hand rail.. that has the fuel reg attached tho... Its the reason you want the right rail.

Also you have to get v1/2, as 3/4 dont match which dont entirely match 5/6.

Give some thought to how you are going to mate the fuel line to the fuel rails as well... i.e the aftermarket fuel line ends.. or just creating a lip on the stock steal line..

It takes a good while.. allow a whole morning. Its the fiddling round making sure you have clearance under the manifold that takes the time and getting the bits of hose all the right length.

Did mine (v3) and took 2-3 hours.. did a mates RS and took nearly 8h.. it was lots harder.

PM me if your just in wellington and i can show you a few things / places to get the bits etc.

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i would say not.. Is it a BD or BG? Im pretty sure they use the same as the version 3 engine and the rails will be different. Pulling out your manifold (and trying) will confirm this.

Perhaps the BD will fit and not the BG.. Not entirely sure on that one sorry.. Basically the mounting points from the rail to the manifold change.

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 matty981 said:

ok im sadly not in wellington. ive got a tool to flare pipe ends. that should be sufficient to do the fuel line ends?

I wouldn't flare the ends of the cut rails to fit fuel hose over. You run the risk of the flared end cutting the inside of the fuel hose. It is possible to get a tool that leaves a similar swage as the end of the factory fuel lines where the hose normally is fitted. Can be hard to find though but is the only safe option when cutting up the factory steel fuel lines.

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 funkytown said:

i would say not.. Is it a BD or BG? Im pretty sure they use the same as the version 3 engine and the rails will be different. Pulling out your manifold (and trying) will confirm this.

Perhaps the BD will fit and not the BG.. Not entirely sure on that one sorry.. Basically the mounting points from the rail to the manifold change.

BD/BG are the same car lol, sedan/wagon.

The early (pre RSB/GTB) BD/BG had the greys and v1/2 rails, Ive used them on the BC RS manifold I have now.

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  • 2 weeks later...

ok just a quick Q for my brother in wellyz....he's decided he wants to be flash and use an aftermarket reg...i told him to use 2 left hand rails for his V4 sti engine. can he use a rail from v1-v2 or just v3-v4....also he seems to think his engine is RA does that mean he should have a 5th injector also?? thanks

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 1992-RS said:

ok just a quick Q for my brother in wellyz....he's decided he wants to be flash and use an aftermarket reg...i told him to use 2 left hand rails for his V4 sti engine. can he use a rail from v1-v2 or just v3-v4....also he seems to think his engine is RA does that mean he should have a 5th injector also?? thanks

he will need v3-4 rails, v1-2 are different.

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 wrx_lou said:

Has anyone run two left rails with one stock fuel reg??

this defeats the purpose of doing the split rail?! (just thinking about the logistics of it..)

also the regs dont fit on the ends of the left side.. I tried it... Only v1/2 have the screw on ends on both side.. V3/4 are all one peice.

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 wrx_lou said:

Has anyone run two left rails with one stock fuel reg??

If you jimmied up something so that both lefts fed back to the single stock regulator (which would need to be remotely mounted somewhere) it could work. The cost of all the extra fittings (and the extra work required) would just make it easier to use two right hand rails with reg's.

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