Fuel pump rewire == very high fuel pressure; upgrade fuel lines?

[karbon]

If you want, just skip down to the question a couple paragraphs below:

First of all, it'd be a good idea to list my fuel setup as it stands: Walboro 255, SX FPR on 1g fuel rail, stock lines with FP gauge on filter, RC 550's.

Now here's what I did and what happened: fuel pump rewire resulted in ~50psi fuel pressures. SX FPR would not go any lower. This tells me that it's the lines (or the fittings) themselves that are causing this. I uninstalled the rewire except for the bigger ground connection and got around 38 psi so I was pretty happy at that point since it was at 35 at idle before anything was done to it. I talked to someone about this and they told me that in fact the stock fuel lines and fuel rail are very restrictive and cause hige fuel pressures that you can't adjust down with an FPR. The only solution is to get bigger lines and fittings from tank to rail. I was considering purchasing the SBR tank-to-filter and filter-to-rail kits and going -6AN all around.

Question: Is it enough to replace just the supply side of the fuel delivery system or do you have to custom build a return system as well to allow for some adjustment via your FPR? From what I read on the forums the reason why we need our high flowing pumps (and injectors) is to overcome the small diameter of the stock fuel supply system. I have also been told that the real bottleneck is the return part of the system. This is why I am asking about that in particular. I imagine that we would not need such powerful pumps and high flow injectors if we put some money into a less restrictive fuel system.

 

[joeracer321]

if you cannot get the fuel pressure any lower, it may mean that you have a blockage somewhere in the return, or a problem with the regulator itself. I don't think increasing the supply line would lower pressure, it would increase volume of fuel available which is always good, but the same pressure would build if a problem somewhere in the return exists.

 

[karbon]

if you cannot get the fuel pressure any lower, it may mean that you have a blockage somewhere in the return, or a problem with the regulator itself. I don't think increasing the supply line would lower pressure, it would increase volume of fuel available which is always good, but the same pressure would build if a problem somewhere in the return exists.

That's true. As long as a blockage is not in the return line, replacing the equipment will flow the same amount of fuel at lower pressures. I'm thinking of replacing the filter anyway with the Mr. Gasket unit with the 6AN ends anyway. I also got a heads up from Cragger at Slowboy saying that moving the FPR off of the end of the fuel rail will help a lot.
Thanks for the reply.

 

[psychlow]

Yeah... if you can't get your fuel pressure down with an AFPR, there is an issue with the AFPR, or the return line is too restrictive.

As a benefit, though, if you upgrade the feed line, you'll get much better flow due to ditching the crappy stock fuel filter.

 

[karbon]

Yeah I was thinking of the Mr. Gasket 6AN fuel filter on SBR. Every once in awhile I'll get a single violent stutter at partial throttle boost. I replaced the plugs and am thinking about wires (need some 10mm wires because of the MSD DIS, but I'm hoping the fuel upgrades would rectify things and make them better at the same time. We'll see.

 

[4geze63]

I have -6an line from tank to fuel rail, high flow fuel filter with a walbro 255 no rewire. My return line clamps onto the existing return line. works fine. I can lower fuel presure with my fpr, i thought the SX was just like Aeromotive

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[dave99gst]

ive got a rewired 255hp with -6 AN lines 1g rail and spoolin-up FPR
i can control it no prob also.