Fuel system

I’ve seen the fuel lines run a couple ways. Y before the fuel rails (parallel) and fuel rails fed in series. Is there any difference, pros or cons to each way?


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I’ve seen the fuel lines run a couple ways. Y before the fuel rails (parallel) and fuel rails fed in series. Is there any difference, pros or cons to each way?


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Oh man my instinct is to say parallel, but I have no proof. I know a certain engineer that will chime in for us :)
 
Parallel... I can't imagine the last injector in a series is getting the same amount of fuel as the others....
 
Oh man my instinct is to say parallel, but I have no proof. I know a certain engineer that will chime in for us :)

I’ve seen quite a few builds done both ways. Mine is currently parallel but that “certain engineer” asked me about how my fuel system was routed and it has stuck in my head. Just makes me wonder if there’s any difference.


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Parallel... I can't imagine the last injector in a series is getting the same amount of fuel as the others....

That’s my instinct as well. But practically I think the pressure should remain the same as long as the lines are big enough. Still curious though.


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If you got enough pump if don't matter which way it runs. My truck is parallel but on our gen2 it's in series.

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I’m sure there is more to it then that as well.

Single in regulator vs dual inlet regulator.
Size of the lines goin in/out or from one to another in series.
Size of injectors.


I always compare it to my home water pipes in my head. If you have a long run with multiple taps (compared to a system with home runs) you always have a pressure drop at a device for a moment when another valve is opened (until the pressure equalizes or recovers). Whether that’s correct thinking or not that’s what I think.
 
I’m sure there is more to it then that as well.

Single in regulator vs dual inlet regulator.
Size of the lines goin in/out or from one to another in series.
Size of injectors.


I always compare it to my home water pipes in my head. If you have a long run with multiple taps (compared to a system with home runs) you always have a pressure drop at a device for a moment when another valve is opened (until the pressure equalizes or recovers). Whether that’s correct thinking or not that’s what I think.

Makes sense. I never thought about it quite like that.


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It won't make a huge difference either way.

As long as you have enough pump, each injector just sees the rail above it as a "plenum." There will be a tiny pressure drop every time an injector opens, but that's offset by a tiny pressure surge every time it closes. You'll end up with a pretty constant average pressure that's determined by the regulator. If your supply line is the same size as the ID of the fuel rails, it also won't make a difference. If you feed with a larger line, then parallel makes more sense.

If you don't have enough pump, and pressure starts to drop, it becomes a bigger issue, and you're going to impact the furthest out injectors the most.

All that said, I run an AN8 feed to AN8 rails in parallel, and then twin AN6 returns to the regulator with a single AN6 back to the tank.
 
Thanks for your wisdom Jeff.

Good video Jason.

To sum it up.
If your feed line(s), fuel rails, return line, and pump are properly sized for your system, then running the rails in parallel or in series is perfectly fine.
If your pump cannot supply the pressure and volume required, the pressure differential between cylinders may be magnified by running in series.
Running a large return line allows the least amount of back pressure behind the regulator, allowing the regulator to work more effectively.


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