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Discussion Starter · #1 ·
Here's the discussion of the day. :)

I threw up a thread this morning wrapped around the return fuel system in my 98.

http://www.modularfords.com/showthread.php?p=1327799#post1327799

Someone asked me an interesting question to which I didn't know the answer, so I thought some of you might want to throw in your 2 cents, since so many 03+ Cobra guys switch over to a return style system.

The conversation was regarding the way you feed the rails. Some people dead head the rails, some people (like myself) feed the drivers side rail from the tank, cross over at the front of the rail, and exit to the regulator at the back the passenger side rail, while some people Y block into the rails on the way in, then Y block back down to the regulator on the way out.

So you've got:
1. Deadhead
2. In Series
3. Parallel

In doing it the second, and my current setup, do you have to worry about a significant pressure difference across the injectors from front to back?

Here's the other side of the discussion's question:

[URL="http://www.stangsofsouthflorida.com/forum/member.php?u=300" said:
raslobra98[/URL]]The reason I ask is that running the fuel rails in series rather than parallel gives a pressure differential across the rails.
Now even if you ran them in parallel you would get a small pressure differential from the back to front anyway. (feed to return anyway)

The key concern is:
Is this pressure differential negligible or will 4 83lb injectors draw enough fuel out at WOT to cause a considerable fuel pressure drop to the next rail.
Which would then lead to inconsistency (a function of this pressure drop) from bank to bank and even front to back cylinders, when considering Air/Fuel mixture.

The problem is not having enough fuel, but rather what a fuel pressure means to the injectors. When it comes to tuning you would have a lot of fun....
I believe the tuning software accounts for injector duty cycle dependent across a constant input pressure. (basically assumes all cases equal).
Side note: if it were a German car, they would account for this.

I would much rather run my lines like you have them, but being a mechanical engineer (and it sounds like you know may be one as well with your thermo talk) I'd like to know the effect of this.

Have you looked into this or have experience from others that know this is not a problem?

From my experience, I would say that a 1-3psi difference is OK but anything greater is not good.
I know that 5psi makes my car go from 14.7:1 to 14.2:1 (A/F) at idle and at WOT goes from 12:1 to 11.5:1 (A/F).

And if your wondering what I'm talking about, its my lazy way of tuning when I don't feel like getting out the PRP to adjust the base fuel curve at higher RPM's (basically flooding the system slightly richer at all RPM - I don't recommend doing this). I'm just using this for the reference of how the pressure effects the A/F

The slight adjustment of 5psi at the FPR drops the A/F .5 richer.

So if I am making any sense, for instance, you could be running 12:1 A/F (somewhat safe) at your first few cylinders the fuel reaches to possibly 12.5:1 A/F (typically not safe with 15psi boost) at the last few cylinders.
Any and all input is welcome. :)

Thanks,
Alan
 

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The key to any good fuel system is volume.
It only makes sense to 'Y' the feed line to both rails.
Do it once, do it right the first time.
 

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Dead head will be for a returnless system, you can't deadhead a return setup to my knowledge.

You are holding pressure on the fuel system after the fuel has left the rails so both sides should be seeing that psi of pressure or very close. You would have to lose a lot of fuel to cause a big drop on the feed side if in series fed system.

I went series on mine due to space and cleanliness around my blower inlet. My cross over is at the rear and I feed the passenger side front rail and exit out the front of the driverside rail into my regulator.
 

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Discussion Starter · #4 ·
The key to any good fuel system is volume.
It only makes sense to 'Y' the feed line to both rails.
Do it once, do it right the first time.
Flow, I think is what you're looking for.

Pressure is also a consideration.

Dead head will be for a returnless system, you can't deadhead a return setup to my knowledge.

You are holding pressure on the fuel system after the fuel has left the rails so both sides should be seeing that psi of pressure or very close. You would have to lose a lot of fuel to cause a big drop on the feed side if in series fed system.

I went series on mine due to space and cleanliness around my blower inlet. My cross over is at the rear and I feed the passenger side front rail and exit out the front of the driverside rail into my regulator.
I think yours is the same as mine, only the crossover is in the front of mine, not the back.

 

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My set-up -8 feed from regulator to passenger side front rail -6 return from regulator to drivers side front rail. crossover is in the rear much cleaner looking this way
 

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Mine are fed with -10 from the A1000, into a Y , 2 -8's out of the Y into the rear of the aeromotive rails, with 180* fittings on the front of the rails, essentially running the lines right back over the rails and out of sight, through the fenderwell area and back into the regulator, with a single -6 return. I would feed both rails, most definitely not feeding them in series, especially if you are running 83 Lb injectors most likely in a high boost situation!!! In lower boost apps, I am sure it is ok, but it is not worht the gamble if you plan to make big power. Big power requires big time fuel with consistent volume and pressure.

Good Luck, James
 

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My new Glenns system is like this:

A -10 to the filter then into a Y which ties into the 2 Walbro pumps. then each pump feeds a -6 line to the front of the car and one into each rail, come out of each rail with a -6 then they both enter the reg. Out of the reg is one -6 which returns back to the tank. Setup should handle 800+ to the tires.
 

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My new Glenns system is like this:

A -10 to the filter then into a Y which ties into the 2 Walbro pumps. then each pump feeds a -6 line to the front of the car and one into each rail, come out of each rail with a -6 then they both enter the reg. Out of the reg is one -6 which returns back to the tank. Setup should handle 800+ to the tires.
Mine's pretty similar. Mine is -10 feed from glenns sleeper tank into filter out to y block to 2 walbro pumps to another y block into post-filter and out to a -10 feed up to another y block. Then from y block, 2 -8's run into front of rails. -8's out back of rails into an aeromotive regulator. -8 return out regulator back to the tank. All aeroquip pushlock line and jegs fittings.

I'm not a fan of the single feed line per pump, but a lot of people seem to do it with no problems (similar to the crossover on the rails vs running each rail out to the reg individually). If one pump cuts out there's a chance you can go lean on one bank since you are feeding each rail with a seperate pump. With a single feed and y-ing out to both rails, you are feeding them equally so even if 1 pump cuts, you are feeding both rails equally still.
 
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