EFI Fuel Plumbing

[PFM]

All,

Long time no visit. I am working on a flat 6 cylinder (Porsche) adding a second set of injectors. Due to location a "fuel rail" is impractical and this prompts my question: Are short fuel lines (-6) from a central supply block a big problem? I do understand the fuel in this line is "trapped" as it will not be in the return loop for the regulator but are there any other issues? This is a track only application.

Thanks in advance,

PFM

 

[WGJ]

As usual, trapped fuel (i.e. no recirc line) leads to trapped vapour, unless the fuel pressure is high. Modern mechanical returnless fuel systems seem to be in the 4 to 6 bar range.

Bill

 

[howboycat]

Why not run a return from the supply block?

 

[PFM]

All,

There will be a return line from a distribution block(s) located within 3 to 4 inches of the injector. So fuel line from pump to distribution block, hose to second bank distribution block, hose to regulator and bypass to tank. From each block are three lines 3 to 4 inches long -6 hose to the individual injector. The question is does anyone see this as a problem versus a conventional fuel rail attached to the injector. Fuel pressure will be about 50 PSI.

Thanks for the replies,

I hope this makes the question clearer.

PFM

 

[patprimmer]

That sounds not to different to the system used on early FI air cooled VWs. They had no problem.

Regards

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[PFM]

Pat,

I have seen you on this board for years, thanks for the reply. I have one of those early flat fours with FI. They could not be considered high performance and this application is. I have heard all kinds of stories about fuel delivery problems, resonance troubles etc. just trying to find truth.

PFM

 

[pmrobert]

Personal experience with this scheme is that it's worked fine for >25K miles on a Mazda rotary in a warm climate over the last 4 years or so. I have about 4" of line between the supply block and each injector.

 

[patprimmer]

I am presuming heat soak into the fuel line is the anticipated problem. The higher the fuel flow, the less the residence time. I do't see a real difference that makes the Porsche application any more difficult.

It has higher fuel pressure and higher fuel flow and probably higher air circulation in the engine compartment due to higher speed and higher rpm.

Regards
Pat
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[IceStationZebra]

I assume the junction block is higher that the injectors, which would let any vapor rise to the block.

ISZ