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I6 to Dual feed or not to dual feed

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Seen this discussed on many supra/rb/bmw forums (pretty much any Inline 6 engine car) whether to feed the long fuel rail from each end and return in the middle, or whether to feed from one end and return at the other OR feed from the middle and return at the ends. I'll do my best to summarize each option's pro's/cons

Dual Feed, center return: kinda old school, allows max of 3 injectors in a row. According to Hypertune, Aeromotive and other reputable companies this is actually bad because when the fuel meets in the middle (at speed) it creates a turbulence that can affect the injectors near the merge.

Single Feed, Single return: Simple, less fittings and hose, OEM install method. Puts 6 injectors in a row which commonly sounds like there will be less flow/pressure available to the far end.

Single center feed, dual return: not a very common install (to my knowledge), max 3 injectors in a row. More fittings used then straight through. Can't really see a down side otherwise.

I have yet to see any hard data on this, just a lot of people claiming one or the other is better. I would love to throw like 8 pressure senders on a system and see if theres a measurable difference anywhere.

I have an opinion but I want to see what others with different experiences etc have to say before I colour this thread with my theory.


Hello i have used all of these methods over the years and have seen no difference in doing it either of these ways

i like to keep things simple now so just one in and one out and I don't short change the effect of having the rest of the fuel system up to the job i want it to do, it is really important to match the correct lines, fuel pump and regulator to any build

I agree Ross.

My 0.02;

Your fuel system should be sized properly and maintain pressure even at full flow. This means that there will always be flow in the return line and pressure at the regulator. Having your pump sized properly to maintain flow at pressure under boost and not forgetting that theres a bit of pressure drop along the lines.

Fuel pulsation dampers are meant for dealing with acoustics within the fuel rail and OEM hard lines. If you're swapping in rubber lines or even stainless braided rubber lines, this usually solves that problem. Paul Yaw did a talk at SEMA one year for Injector Dynamics and covers this well. Find it on youtube.

For me, I'm into simplicity and less cost in AN lines. Straight in and out, no Y. Simple, and very effective if the system is built/sized well. If the pressure regulator is doing its job the rest of the system before it shall be at the same pressure (or even slightly higher but in the case of the rail its the same) at each injector.

This has been my experience and is not concrete fact. One day maybe I will put 8 pressure sensors in a rail and gather some data to compare.

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