The return line must be at least as big as the supply line, minimum. Otherwise the return hose becomes the restriction. And if you are using a high GPH for application pump, it should be one size larger.
I've heard this before, but many don't agree w/ this. One of the engineers at Aeromotive recommended the -10 feed and -8 return on my car and it works flawlessly.
Many factory EFI applications use a smaller return than feed also.
So I'm curious as to why different people give different answers and I go look at Aeromotive's stuff since I'm not real familiar with it and I might learn something. Lord knows I'm wrong sometimes.
I see Aeromotive makes a variety of return style regulators designed for different GPH pumps. in the instructions for their 13204 carb bypass regulator, these lines...
"The enclosed Aeromotive regulator was designed to be used with fuel pumps up to 150 gph, similar to
Aeromotive P/N 11101. Performance may be degraded if a similar pump is not used-"
"Attach the fuel return line to the AN-08 bypass port located at the bottom of the regulator using a cutoff AN-08 style
fitting (Aeromotive P/N 15607 or equivalent) and o-ring. The by-pass line back to the fuel tank must be no smaller
than AN-08 size."
Then in the instructions for the 13224 reg, this, along with a chart...
"The enclosed Aeromotive regulator was designed to be used with fuel pumps up to 250 gph, similar to
Aeromotive P/N 11101 or 11104. Performance may be degraded if a similar pump is not used."
![[Linked Image]](https://i.imgflip.com/7bfntq.jpg)
The big 13212 reg for 300+ GPH is made for all -10 stuff.
Keep in mind the -8 hose from any of these places is 1/2" ID at best. Some are smaller.
SO, the answer to "how large should the return line be?" is, depends. But it certainly can not be too large.
