Passing along info I have learned -

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.

Tank to pump, one size larger minimum than supply line.

Tank vent minimum -8.

Much easier on the pump to maintain volume at <10psi than at >25psi.

We build a system to that spec, works perfectly. Fuel pressure rock steady on the Racepak. Fuel doesn't heat soak in the line. Put a diptube on the return in the tank, get a solid fuel flow with no aeration.

On a dead head system, fuel in the supply line just sitting there, for the most part, until the hit. What's that fuel weigh? It has to be accelerated in the line to meet the demands of the engine. Plus it has to be accelerated against the G forces of the car accelerating. With a return system, it's already moving.

I ran deadhead systems forever. They work. Won't anymore unless the guy insists. Heck, I have guys running low 9s at 3600# with Holley Blue pumps.

Tank in the front of the car makes things much easier.

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.

I don't disagree that someone would tell you that. The tech guy I talked to at a company that builds high end carb fuel systems we've used told me same or larger. Along with the rest of it. You'll get different stories from different places, even though they are the ones who design, test and make the stuff.

My thoughts were, if you run it up through 16' of -10 and return it through 16' of -8, how can the smaller line not be a restriction, to some degree, with a big pump? I want to control fuel pressure at the carb with the regulator, I want it to be consistent regardless fuel demand of the engine and we aren't running a lot of fuel pressure to the carb.

Not all return regulators and systems are designed the same way. Different parts and pieces from different manufactures will function differently.

We monitor fuel pressure at the pump outlet and the return side of the regulator. There's always more than one way to do something. I'm happy with what we have.

I agree. If what you have works, who is to argue that? The bigger return line makes sense to me too.

Mine is the same set up as yours.

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."





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.

FWIW I can get one brand talked about here a lot for FREE . But I choose to run the Weldon stuff....

They are top shelf. No doubt.