Parrallel Fuel Mod...??

georryan · Post by **georryan** » Fri Sep 12, 2003 4:07 am

I looked and couldn't find anything on it, so I hope I'm not out of line in asking this....

What is this parrallel fuel mod exactly? How does it work in relation to the way our current fuel injection works? How does it increase power?

mTk · Post by **mTk** » Fri Sep 12, 2003 4:23 am

from scoobymods:

Reasons Behind The Modification:

1. Current system on the Impreza runs in series, mod will convert to parallel

2. No one injector will get less fuel then another one

3. The 3 rd chamber will not run lean as it always has in the past

4. Highly recommended mod for people building up a Turbo for their Impreza.

5. We think you get a little bit of Hp increase but we can not prove it

6. It’s cheap and fun

The Site

mk

mTk · Post by **mTk** » Fri Sep 12, 2003 4:25 am

Basically it's a safety measure to prevent the last cylinder in the fuel rails from getting less fuel than all the others, thus preventing a premature failure in that cylinder.

MK

georryan · Post by **georryan** » Fri Sep 12, 2003 5:19 am

ah thanks.

Post by **Legacy777** » Fri Sep 12, 2003 1:52 pm

I'm not sure if the procedure on scooby mods is exactly correct for our cars. I have been looking at it, and seeing how to do that on my car. The big hiccup is the weapon-r adapter he talks about. I can't find that anywhere, nor any mention of it.

If you can leave the stock fpr in it's orig location, then you couple probably rig something up that would work. I'm waiting for Rod to finish his up, and see how it looks, and I will probably do mine when I take the intake manifold off to do the injector work I need, and to replace the gaskets.

mTk · Post by **mTk** » Fri Sep 12, 2003 5:09 pm

I also wasn't able to find the weapon R adapter, but it shouldn't be hard to attach a hose. Once i take off the intake manifold and poke around a bit i'll know for sure how it goes.

MK

Post by **Legacy777** » Fri Sep 12, 2003 11:17 pm

if you leave the stock fpr in it's location, yeah it's easy to attach a hose, but if you remove it, then it becomes more difficult.

THAWA · Post by **THAWA** » Mon Aug 02, 2004 6:09 pm

BUMP!

I mean, so how would you leave the stock frp inline and still have it setup in a parallel fashion? Also just to be sure it's not completely parallel. From how it was reading and the pictures it looked like injectors 2/4 and 1/3 were still in series with each other. Is that right? I'm almost confused about how he did the lines, it looks like he has it setup so it comes from the filter, then t's to 2 and 1, then that follows the rails through to 4 and 3 (could be backwards on that). which then ts back to the fpr and flows back to the tank. Would it matter which way the fuel entered the rails? Like since the stock setup has it entering 4 first and exiting 2, then entering 1 first and exiting 3 would it be harmful to anything if it were to enter 2 first and exit 4, or enter 3 first and exit 1? I assume the vacuum hose is for the CPS valve, is thtat right?

also as far as the fpr adapter, go here: http://www.weapon-r.com/ then power>racing performance>fuel pressure regulator, then scroll down a bit. There isn't one for subaru but the nissan one might fit.

vrg3 · Post by **vrg3** » Mon Aug 02, 2004 8:27 pm

I think you have the flow paths right. You do end up with two series pairs of injectors which are in parallel. Uh, yeah, that's not an abuse of the English language.

I don't think it matters which way the fuel flows through the rail.

I know from experience that a 94 Nissal Altima FPR bolts right onto a 92 non-turbo Legacy passenger side fuel rail. The hose barb comes off at a different angle, but that doesn't matter; the Nissan adapter should work fine.

I don't know what you mean about the vacuum hoses... Both the FPR and the CPS have vacuum hoses going to them, but the CPS' doesn't go to the intake manifold; it goes on top of the throttle body.

Wait a minute... I have a question.

Isn't our fuel injection system sequential? With sequential port fuel injection on a 4-cylinder 4-stroke engine, only one fuel injector should be open at a time, right? Then why should the series setup matter?

Does our system switch to nonsequential at high RPMs like some other cars? Or is this parallel fuel rail mod only important for people who have switched to nonsequential aftermarket ECUs? What am I missing?

rsstiboy · Post by **rsstiboy** » Mon Aug 02, 2004 10:12 pm

I am only running 1 rising rate fuel pressure reg and 2 driver side fuel rails (modified of course

) I'll post up pics of how the finished product looks......

TDGKORN · Post by **TDGKORN** » Mon Aug 02, 2004 11:20 pm

vrg3 wrote:
Wait a minute... I have a question.

Isn't our fuel injection system sequential? With sequential port fuel injection on a 4-cylinder 4-stroke engine, only one fuel injector should be open at a time, right? Then why should the series setup matter?

Does our system switch to nonsequential at high RPMs like some other cars? Or is this parallel fuel rail mod only important for people who have switched to nonsequential aftermarket ECUs? What am I missing?

I'm with you vrg3 I thought we are sequential so it didn't matter.

mTk · Post by **mTk** » Mon Aug 02, 2004 11:35 pm

It needs to have atleast 2 open right?

MK

free5ty1e · Post by **free5ty1e** » Mon Aug 02, 2004 11:45 pm

so how different is the Impreza's mod instructions from what we'd actually have to do on the Legacy?

Post by **Legacy777** » Tue Aug 03, 2004 1:33 am

Guys.......I looked into this.....the write up really won't work.....the big thing is because of that weapon r adapter.

If I were going to do it, I would do as rsstiboy mentioned. Use two driver's side rails. Get a piece of an extra set of fuel rails that you bolt to the rail in the rear (where the fpr was). Repipe the fuel lines with rubber fuel hose, so that each open end of the fuel rails come to a barbed T. So you now have two inlet points.

Use an adj fpr with two outlets, and just run fuel hose from the fpr to the two inlets.

Simple....and effective. Reason I didn't do it....didn't have an extra set of fuel rails and lines laying around.

THAWA · Post by **THAWA** » Tue Aug 03, 2004 5:05 am

for the vacuum line I meant what did he need it for in the list. As for the sequential thing. I had thought that since the #3 cyl was the farthest from the fuel source it ran lean, but that sounds kinda like a fpr issue now that I think about it, doesnt it?

free5ty1e · Post by **free5ty1e** » Tue Aug 03, 2004 2:19 pm

I think #3 going lean because its the furthest down the line from the fuel source.... is a reason. It's not the only reason though. I doubt that just happens simply because its the furthest down the line. I think a clogged fuel filter or failing fuel pump would probably begin to manifest itself by not being able to always get fuel to #3, which causes a more serious problem before the filter completely clogs or the pump completely fails.

Am I making sense, or am I talking from my other oriface again?

- any of you guys with lean #3's, did you have a fuel pressure gauge goin? Did you notice it dropping, not able to keep up sometimes? My fuel pressure gauge is goin in soon I hopes.

evolutionmovement · Post by **evolutionmovement** » Tue Aug 03, 2004 3:06 pm

I've replaced fuel filters before and they always manifested themselves with hesitation. The fuel pump could be going on mine as it's original. I don't know if there's some way to see if it's another issue instead.

Steve

mTk · Post by **mTk** » Tue Aug 03, 2004 3:14 pm

Not sure which cyl it is, but there are too many cases of that same cylinder always going lean and ruining the engine to overlook the possibility.

MK

THAWA · Post by **THAWA** » Tue Aug 03, 2004 3:47 pm

it's generaly #3

vrg3 · Post by **vrg3** » Tue Aug 03, 2004 4:03 pm

Why would it matter that it's "furthest from the source" though, if only one injector is open at a time anyway?

It's closest to the regulator. Should that matter?

mTk · Post by **mTk** » Tue Aug 03, 2004 4:06 pm

Fact is, it happens, cyl goes lean and piston is destroyed. When parallel rails are installed, it is gone. Explain that?

MK

THAWA · Post by **THAWA** » Tue Aug 03, 2004 4:09 pm

thats what i was wondering. it sounds like a fpr thing. But then again if the pump couldnt keep up, like say it needed to send out 100 units of fuel, but could only pump 80 units, wouldnt that affect all the injectors? Like there would be less pressure all ariound instead of less in one cyl. It might make more sense to find out what the other cyls fuel pressure/af ratio/ something is before just assuming it's the problem. hell it could be an oil thing, or a cooling thing, or it could be a combonation of a lot of things.

Post by **Legacy777** » Tue Aug 03, 2004 6:07 pm

I'd say it's a combo of a lot of things.

You can say that cylinder is going lean....but if you got a pump that can't supply adequate fuel flow and maintain proper pressures then how can you blame the fuel rail setup?

If you really wanted to scientific about it, you would need to get pressure readings at multiple points on the rail. You'd probably also want to do this before and after adding a larger pump to see if that has any affect If after the larger pump it doesn't seem to affect things, then I would say it's the rails, and possibly could be some sort of pulsation where the #3 cylinder doesn't get the proper amount of fuel. In which case redoing the fuel rails would solve the problem.

rsstiboy · Post by **rsstiboy** » Tue Aug 03, 2004 10:13 pm

Ideally I wanted fuel entry points at BOTH ends of each rail, just for extra security, but running 4 fuel lines and 3 t pieces just wasn't gonna happen, so I opted for the way I went.

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Parrallel Fuel Mod...??

Parrallel Fuel Mod...??