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Should you run fuel lines in series or parallel?
Should you run fuel lines in series or parallel?
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Old 07-12-17, 04:50 PM   #1
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Default Should you run fuel lines in series or parallel?

​I am in the process of finishing my build for my birthday 06 WRX and looking to ask the question in regards to fuel line configuration.

I will have a 550 whp capable turbo running e85, wanting to know for such a setup should I run the fuel lines in series or parallel?

From my own reading it seems like a debatable topic as to which is right or wrong, possibly. But that is why I am trying to gather more information and also ask the community who is very knowledgeable so I can make sure that I make an informed decision.

Thanks
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Old 07-12-17, 05:55 PM   #2
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Default Re: Should you run fuel lines in series or parallel?

Even though I replied, I'm not arguing one way or another - but a start for your searches

Fuel rails
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Old 07-12-17, 07:25 PM   #3
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Default Re: Should you run fuel lines in series or parallel?

I only went parallel because I was rebuilding and decided to follow theory. At my current point in the build, it's total over kill, and probably still over kill later, but I prefer that than short changing myself. In theory, parallel is better, but as the thread linked by mheyman shows, I can't prove it.
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Old 07-13-17, 02:44 AM   #4
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Default Re: Should you run fuel lines in series or parallel?

Quote:
Originally Posted by mheyman View Post
Even though I replied, I'm not arguing one way or another - but a start for your searches

Fuel rails
mheyman thanks, I did a search and did not see anything really. However I did not do fuel rails as the search I just tried keywords series and parallel. So no idea why it would not have come up. I saw posts in marketplace but nothing in threads. I will have to take a look at it and read it over. Thanks for the link I really do appreciate it.
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Old 07-13-17, 03:00 AM   #5
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Default Re: Should you run fuel lines in series or parallel?

Quote:
Originally Posted by Noximus View Post
I only went parallel because I was rebuilding and decided to follow theory. At my current point in the build, it's total over kill, and probably still over kill later, but I prefer that than short changing myself. In theory, parallel is better, but as the thread linked by mheyman shows, I can't prove it.
Noximus thanks yeah I think if I went parallel it would be an overkill as well. But then again I do not know and that is what I am trying to figure out. Since I only want what is best and also reliable for the long term for my car. So which this debate continues. Definitely going to have to read over link mheyman sent.

Also do you guys know if you do decide to go parallel after the fact if you already finished the build (Not really an issue if during build), but if you end up putting the T splitter to split the fuel lines heading to each fuel rail. Does it matter if it is not equi-distance from each fuel rail and equi-distance from the fuel rail to FPR? What happens if you put the T splitter so it is closer to one rail than another, etc does it matter much in the end game or is it still good just because it is in parallel?

Also someone local suggested that reverse series, I have not heard of that and was wondering if that would make sense? Said it works better and parallel is over kill. Never heard of this setup so something else.
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Old 07-13-17, 03:25 AM   #6
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Default Re: Should you run fuel lines in series or parallel?

What year is your STI?

In the past "all" STIs had a terribly annoying resonance created stumble just below 3k. It's severity would change depending on conditions but would rarely go away entirely. Back then it seemed the people who successfully eliminated it had replaced their entire fuel system and all the ones I read of had gone parallel. YamahaSHO claims it was due to a dead head, but I have never seem it explained.

Keeping paralleled lengths equal helps insure equal return volume, but to his might not matter. I do know from experience working with cooling water in instrumentation that line lengths will change pressure and volume of otherwise similar cooling paths. It will also help insure that if you have solved any resonance issues on one side the other is the same, and not on the verge of problems. That said our fuel lines are short and they shouldn't make much difference. There was a lot of trial and error going on in the past.

Subie shops, at least better ones understand the issues and can probably build decent systems without replacing rails or paralleling lines as Yamaha states.
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Old 07-13-17, 03:41 AM   #7
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Default Should you run fuel lines in series or parallel?

Quote:
Originally Posted by jdkluck View Post
Noximus thanks yeah I think if I went parallel it would be an overkill as well. But then again I do not know and that is what I am trying to figure out. Since I only want what is best and also reliable for the long term for my car. So which this debate continues. Definitely going to have to read over link mheyman sent.

Also do you guys know if you do decide to go parallel after the fact if you already finished the build (Not really an issue if during build), but if you end up putting the T splitter to split the fuel lines heading to each fuel rail. Does it matter if it is not equi-distance from each fuel rail and equi-distance from the fuel rail to FPR? What happens if you put the T splitter so it is closer to one rail than another, etc does it matter much in the end game or is it still good just because it is in parallel?

Also someone local suggested that reverse series, I have not heard of that and was wondering if that would make sense? Said it works better and parallel is over kill. Never heard of this setup so something else.


My builder didn't put my T perfectly centered between the two rails. It always bugged me a tad too much due to OCD not seeing it symmetrical. At one point, I believed I was having fuel issues during the tuning. I sent a note to Aeromotive to ask a question about their FPR, and asked this very same question at the same time. They replied confidently that it makes no difference at all.

Edit: I started seeing the stumble at Stage 1, and it got worse at Stage 2. Replacing the entire setup removed it entirely. I also wanted to add, I went parallel as well simply because I wanted to replace the fuel lines to AN fittings and by buying the kit from IAG it was a no brainer to do it even it had no benefit. You could just as easily go parallel after the fact but you would just need to add some lines.

Here's my setup:

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Old 07-14-17, 05:20 PM   #8
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Default Re: Should you run fuel lines in series or parallel?

I installed the old Perrin parallel fuel lines back in 2012. After tuning the Engine Load Compensation Tables in Romraider, the stumble was all gone.

I tried to make the hose lengths as equals as possible and neat. The lengths are withing 6" of each other. I don't think it makes much of a difference at my power level.
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Old 07-18-17, 11:38 AM   #9
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Default Re: Should you run fuel lines in series or parallel?

I am not an expert... but I had the stumble when I upgraded to ID1000s and a larger turbo. Tried the usual fixes with no success. My solution was to run custom lines in series with IAG's rails with dampers. My FPR sits right at the end of the second rail. I am at 350 WHP (restricted by TMIC) and with no more fuelling problems. See the pic.

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Old 07-18-17, 02:16 PM   #10
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Default Re: Should you run fuel lines in series or parallel?

parallel for equal fuel distribution and pressure across each rail.
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