I recently removed the motor in my car to do some freshening up and decided to upgrade my afpr and fuel lines. My current afpr drops pressure immediately when the vehicle is turned off, whereas most people tell me their regulator holds pressure for at least 10-15 minutes. I will be replacing it with an Aeromotive 13109 regulator.

Regarding the lines, I'm running a -8AN from the pump to the rail. At the rail, it reduces to -6AN. From the rail to the regulator my size stays the same. I am using the stock feed line to return fuel to the tank.

My concern/question has to do with restrictions in my return system. The -6AN fittings I bought to plumb the regulator and over to the return line are obviously not the best quality. The I.D. is considerably smaller than better quality fittings. This totally defeats the purpose of -6 line if all your fittings are less than that.

Anyway, I'm willing to overlook this if I can confirm its irrelevance. The car is making approximately 600hp.

One theory I have... If you've ever taken a fuel pressure regulator apart, you'll notice that the relief valve that opens to return fuel to the tank is miniscule. I mean maybe 1/16". It's very small. (I'm referring to my Aeromotive regulator)

That being the case, is it really necessary to have anything remotely as large as a -6AN, considering that the smallest point within the system is the diameter of a pinhead?

 

I'm shooting for 650-700 on my build. I went with 6AN PTFE line from the walbro 450lph to the filter and rail, and 6an return through a flex fuel sensor and all the way back to the tank.

I got rid of the restrictive hardlines on the tophat of the fuel pump hanger and switched to 6AN bulkheads to get rid of the bottleneck from those tiny lines. Was a bitch to get done and took me about 6 hours of modifying the hanger/test fit/ repeat, but she is finally done.

 

Looks great! I'm doing the same thing at the hanger for my feed. Installing a -8 bulkhead. The return I may run through the stock feed outlet or a weld-in 3/8" barb.

My primary concern relates to the limits of a return system and at what point out becomes a restriction.