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Old 04-07-2011, 10:19 AM   #1
Token-Negro
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Default Series or Parallel Fuel lines?

I did a little poking around but wasn’t able to find a definitive answer to what is the preferred method of running fuel lines on aftermarket rails. Parallel obviously needs way more fittings and takes up a lot more space under the manifold, and series is quick and simple.
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Old 04-07-2011, 01:12 PM   #2
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I would think that parallel "should" give you less of a pressure drop between injectors. I have changed my stock rails to this, but I have not done any real testing.
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Old 04-07-2011, 05:18 PM   #3
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If you're set on going aftermarket with the fuel rails, it makes no sense to keep it a series system.
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Old 04-07-2011, 06:41 PM   #4
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Quote:
Originally Posted by 340Duster View Post
If you're set on going aftermarket with the fuel rails, it makes no sense to keep it a series system.
Well in that statement must be the facts on why series is worse then parallel.
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Old 04-07-2011, 06:45 PM   #5
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Originally Posted by Token-Negro View Post
Well in that statement must be the facts on why series is worse then parallel.
The factory system runs the injectors in series, thus cyls 3-4 are on the end of fuel delivery. Aftermarket systems run parallel fuel blocks to provide equal distribution to all 4 cyls at the same time. With that being said, the factory fuel rail will handle the fuel requirements of most builds. What kind of build are you planning?
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Old 04-07-2011, 06:56 PM   #6
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Quote:
Originally Posted by 340Duster View Post
The factory system runs the injectors in series, thus cyls 3-4 are on the end of fuel delivery. Aftermarket systems run parallel fuel blocks to provide equal distribution to all 4 cyls at the same time. With that being said, the factory fuel rail will handle the fuel requirements of most builds. What kind of build are you planning?
1 and 3 are at the end, not 4

The factory order goes 2, 4, 1, 3.
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Old 04-07-2011, 06:59 PM   #7
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Quote:
Originally Posted by the suicidal eggroll View Post
1 and 3 are at the end, not 4

The factory order goes 2, 4, 1, 3.
Doh... odd numbers on passenger side. You're right, thanks.
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Old 04-07-2011, 08:45 PM   #8
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Assuming there is more needed to run parallel fuel rails, the additional space needed is negligible. There is not "way more fittings" need either. You add 2 Ys, thats it. Considering the amount of crap on the stock setup, you will still be saving space. The amount of hose needed is equal no matter which way you go. One in, one out. The difference is whether you put a Y in the middle and run the tank feed and return from the Ys. The FPR is inline on the return, so there is nothing additional there either. it is actually a cleaner and more logical setup once you are familiar with it.
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Old 04-07-2011, 09:15 PM   #9
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Quote:
Originally Posted by aboothman View Post
Assuming there is more needed to run parallel fuel rails, the additional space needed is negligible. There is not "way more fittings" need either. You add 2 Ys, thats it. Considering the amount of crap on the stock setup, you will still be saving space. The amount of hose needed is equal no matter which way you go. One in, one out. The difference is whether you put a Y in the middle and run the tank feed and return from the Ys. The FPR is inline on the return, so there is nothing additional there either. it is actually a cleaner and more logical setup once you are familiar with it.
I have to disagree here, Parallel with 2 Y's is 12 fittings and series is 6 fittings with Zero Y's. And using 8an lines and Y's does tend to take up a fair amount of space under and around the manifold. Really I'm just looking for the benefit of one over the other complexity isn't an prominent issue.
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Old 04-07-2011, 09:18 PM   #10
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Do you post a reply only reading the last response to your question? Your question has been answered. And if that's not enough, maybe you should check this out http://forums.nasioc.com/forums/show....php?t=1218460
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Old 04-07-2011, 09:43 PM   #11
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not sure where i saw it but it showed a flow map of all the stock fuel system/injectors and was said that subaru compensated for the series fuel rail system in its original design.
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Old 04-07-2011, 10:50 PM   #12
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Quote:
Originally Posted by 340Duster View Post
Do you post a reply only reading the last response to your question? Your question has been answered. And if that's not enough, maybe you should check this out http://forums.nasioc.com/forums/show....php?t=1218460
I'm guessing he simply posted a reply to the most interesting response to his question - which is a pretty reasonable thing to do.

Why so uppity?

Btw, did you read the thread you just linked to? The closest thing it has to an answer is Unabomber saying that there's no point going parallel. Which is about as convincing as your claim that there's no point staying with series.

So you can hardly fault him for perpetuating the thread. And ignoring you.
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Old 04-07-2011, 11:07 PM   #13
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Quote:
Originally Posted by NSFW View Post
I'm guessing he simply posted a reply to the most interesting response to his question - which is a pretty reasonable thing to do.

Why so uppity?

Btw, did you read the thread you just linked to? The closest thing it has to an answer is Unabomber saying that there's no point going parallel. Which is about as convincing as your claim that there's no point staying with series.

So you can hardly fault him for perpetuating the thread. And ignoring you.
I'm not arguing for going parallel. I was giving the OP the reasons behind peoples' decisions on going with an aftermarket parallel system or doing a DIY parallel mod. I also inquired why he was seeking to consider such a route. When I did my build back in November, I did a lot of research myself on this issue, as at the time I thought possibly a fuel issue lead to my engine failure. It was after this I reached the conclusion that the factory setup with a proper pump is plenty capable of maintaining sufficient flow and pressure for the majority of daily driven setups. Without any more information on the OP's build or plans, it is almost impossible to make any recommendations.
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Old 04-07-2011, 11:19 PM   #14
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Guys its like this, we all know people do stuff because they think, or heard, or what ever reason that something is good, or works better. I'm simply trying to make a educated decision based off peoples first hand experience. I found one post that said a guy gained fuel pressure from going parallel over series. But a lot of what people used to determine what was better was not a fuel system with large lines, big pumps and good flowing fittings. Yes 5/16ths is adequate for most builds but in the day of E85 and 2000cc injectors things have changed just a little. Just saying! Ok so Parallel is better but prove it!
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Old 04-07-2011, 11:55 PM   #15
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First hand experience. Go parallel. It halves the cumulative pressure losses.
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Old 04-08-2011, 12:07 AM   #16
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What's there to prove?

Assuming a .1 psi loss per foot of hose, .1 psi loss per connector, and .1 psi loss per injector, a series fuel rail setup would have roughly the following pressures at each injector at 43.5 psi base fuel pressure and 10 psi manifold pressure

injector 2: 54.5
injector 4: 54.4
injector 1: 54.0
injector 3: 53.9

That's a little over a 1.1% difference between the pressure at 2 (first in line) and 3 (last in line).

Meanwhile, with the same pressure losses, a parallel setup would have the following pressures

injector 1: 54.0
injector 2: 54.0
injector 3: 53.9
injector 4: 53.9

That's a .2% difference between the highest and lowest pressure


Now are these pressure losses completely accurate? Of course not. Are they in the ballpark of what a typical setup with 5/16 lines might see? Sure.

With big lines and nice fittings, you could reduce the pressure difference between the first and last injector, but an equivalent parallel rail setup will ALWAYS be more even than series. The more your pump flows and the smaller your lines, the more extreme the difference will be.



Also, you don't need 12 fittings and 2 Ys, you just need 10 fittings and 1 Y, most aftermarket FPRs have the option of having two input ports so you can plumb the rails independently.




Edit: Just checked a calculator. 5/16 line on e85 with a single Walbro 255 (approx 210 L/hr) will drop almost exactly .1 psi per foot (.097 psi/ft according to the calculator). Change to a Bosch 044 or DW300 at 260 L/hr and that rises to .14 psi/ft.

Last edited by the suicidal eggroll; 04-08-2011 at 12:29 AM.
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Old 04-08-2011, 12:39 AM   #17
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OK so sounds like with the above calculations an A1000 with 1/2" fuel lines and rails will see under 1% difference between the first injector and the last in series. Now if i remember correctly my fuel injectors themselves are roughly within 1% of each other so does that wash everything out, sounds like either way will be just fine. Thank you suicidal eggroll for the calculations, and explanations they helped make the conversation much clearer.
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Old 04-08-2011, 01:08 AM   #18
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Quote:
Originally Posted by Token-Negro View Post
OK so sounds like with the above calculations an A1000 with 1/2" fuel lines and rails will see under 1% difference between the first injector and the last in series.
Looks like about .04 psi per foot pressure drop when the A1000 is going full tilt (441 L/hr) through -8 (1/2") lines.
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Old 04-08-2011, 02:40 AM   #19
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Quote:
Originally Posted by the suicidal eggroll View Post
Assuming [...] .1 psi loss per injector
Citation needed.

I like your math, though. It's the most interesting thing I've seen on this topic so far.
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Old 04-08-2011, 03:09 AM   #20
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Ya I just don't see the problem. If you are going through the trouble of installing -8AN (****ING HUGE!!) lines, then your build is probably pretty extensive. Why cut corners and build a half assed fuel system based on a non-issue? I will put it plain and simple: I have a parallel setup and there is plenty of room. Good luck with your setup bud!!
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Old 04-08-2011, 11:17 AM   #21
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Originally Posted by NSFW View Post
Citation needed.
My ass is not open for questioning

really though, you could put any number you want there (as long as it's reasonable), and compute the difference between series and parallel pressure drops. Increase it to .3 psi and you get a 2.2% pressure difference in series, and .56% difference in parallel. Drop it to 0 psi and you get .56% difference in series and 0% difference in parallel.

The point was that parallel will always have a more even fuel distribution, and depending on your pump setup it can start to be pretty significant (especially those guys running a Bosch 044 or DW300 on the stock rails).

There are even rails out there that parallelize the individual injectors, so not only are the rails in parallel, the actual injectors in each rail are in parallel. That's the epitome of balanced fueling, but again it comes down to a question of whether or not you need things that balanced and if it warrants the extra cost of lines and fittings.
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Old 04-08-2011, 11:53 AM   #22
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I like the discussion here, so really when you start putting higher flowing pumps on the stock smaller lines then you really see the difference between the two, on paper. But as you move up to pump systems that flow considerably more fuel the difference becomes more and more negligible, but the difference is still present.
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Old 04-09-2011, 09:26 PM   #23
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With the recent trend of series/parallel rail discussions and the new batch of high flow drop-in pumps available (and with everybody wanting to get the highest flowing pump available, regardless of what they actually need), I decided to add the equations for calculating pressure loss through the fuel lines, including the pressure drop between the first and last injector given line size, rail setup, etc. to my turbo/fuel calculator.

http://forums.nasioc.com/forums/show....php?t=2158062

(tab 4)

It's currently set up for a stock line/rail config on a single Walbro 255, so you can adjust as necessary, see the effect of going to a Bosch 044, DW300, or dual Walbro 255 on the stock lines, etc.

There are references at the bottom of the table to give you the values for the density and viscosity of gasoline and E85, and example line roughness values for stock lines (grossly approximated, though it doesn't make a huge difference) and aftermarket teflon lines.
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Old 04-09-2011, 11:05 PM   #24
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Default hope this helps

I built my own fuel rails and ran them in parallel with an aftermarket fuel pressure regulator no other fuel system changes,the afr on boost went from 12-1 to 10-1 it seems more fuel, same pump. The stock fuel lines look fine for a stock 180 hp wrx, From reading this forum it seems like there is alot of broken pistons, pounded bearings and cracked cylinders. a lot of det ?. I did not want to test stock fuel lines limitations.
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Old 04-10-2011, 12:05 AM   #25
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dorian291,

Picts!
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