For those of you that run a return line fuel system with a fuel cell. Where do does the return line enter the tank compared to the supply line? If your is on the top of the fuel cell do you have a hose/line so the return is submerged?

Mine is on top, but not submerge

On my cars I always get it as far away from the supply port as possible. I also extend it down into the fuel about 3 or 4 inches from the bottom of the tank.

What do you use to extend the line? Alum fuel line?

Most of the time just a bulkhead fitting and a short most likely 8an hose in the tank.

It is your choice, soft aluminum tubing flared to AN 37 degree flare with a AN female fitting or AN hose with a female fitting on it
I haven't ran the return line on my new car yet but I'm thinking a aluminum line ending up about two inches from the bottom

and now for the old guy DUM question of the day..........

i have read, and been told many times by many different people, the return line should be LARGER, SAME SIZE, and SMALLER in diameter.
these have been on successful installations, so if it is successful and works, it must be ok.
i like the idea of larger, or possibly the same size. less likely to cause residual heat buildup in the fuel system.
it is also quite possible a smaller line would work if there were not much fuel being returned to the tank.
so, any return line is better than nothing, depending of course, the system design itself ?

It may need to be determine by the fuel pump makers, call them to make sure

I would use the same size line so it is not an unintended restriction.

Return to the tank below the fuel level prevents aeration.

unfortunately, i have been told conflicting sizes by both the manufacturers and the dealers, depending on what day i called !
just for curiosity's sake, i crawled under my bus to see what kind of setup it had, and it's return line was smaller than the feed. [they are both plastic lines-99 model year] i realize this is just a 3.3 six cylinder, and it's factory designed for that, but that confuses me even more. [if that is even possible ! ]

Just thinking wouldn't a bigger return line be better because it would reduce pressure going back to the tank reduce stiring up thing in the tank a smaller line would more presure comeing out to keep up with the return flow ???

The pressure in the return line is already lower than the feed side. I would think larger to be unnecessary, but personally I wouldn't go smaller than the feed.

Aeromotive directed me to make the return line the same size as the supply. I’m at -8 on both, with -6 from the regulator to the carb. Return is routed to the top front of the cell, but not extended. May be a good idea as it could cut down on aeration.

I wouldn't think fuel would hold the aeration in a moderately sized tank. It's already in there sloshing around.

I have a stock tank w/ a sump for the pickup. I use the stock 3/8" pickup tube as my return, so it's submerged.
I use a -10 feed and a -8 return...as directed by Aeromotive back in 2011 when I installed this system.

Holley told me -10 feed then use -6 return. The fpr is setup that way too.
This is a MPFI fuel injection setup. However I have a -8 in place for the return. So yes there is a bottle neck from regulator, but I already had -8 installed from the last setup.

Found out it depends on the regulated pressure and pump volume.
Have a setup with the older Mallory 250 GPH pump and by-pass regulator, both -8 AN supply and return.
At idle, the fuel pressure would creep up one or two PSI, go from 7 to 8 or 9 psi.
The pump also has a by-pass, so I set the pumps by-pass to just dump a small amount of fuel back into the fuel cell.
Anyhow, I think High Volume pump and low regulated pressure like 6-7 psi, the return needs to be same size or larger than supply line.
Also, non-boosted carb, the fuel pressure is normally just referenced (or regulated) to atmosphere, so fuel line pressure to vented bowl should stay the same under different loads.
Anyhow, the pressure in the return line has to be lower than the regulated pressure, and pressure is a function on fuel volume, line diameter, and line length. Because the regulated pressure is only a few psi, the return line can't have much pressure in it, or pressure will start to increase.


On my EFI stuff, it is different. The normal 225 lph pump is only about 60 GPH, and "regulated" pressure is 3 or 4 bar = 43.5 psi or 58 psi. By "regulated", that is usually referenced to manifold pressure, so the regulated pressure stays the same across the fuel injector (on return type EFI), but if you have a pressure gauge in the line it only shows the 3 or 4 bar pressure when the engine is not running. Under vacuum the gauge pressure will look lower because the gauge is referenced to atmosphere not manifold pressure.

Anyhow, the largest EFI pump I tested on my car was the Walbro 450 lph (about 119 GPH) at 4 bar with 3/8" supply and 5/16" return and the smaller return line was not a problem.
Because the regulated pressure is way higher, a small amount of pressure in the return line is not an issue.

The return regulator (carb) I have says to check the return line size by running all fuel bypassed (unscrewed 4 turns) with carb lines plugged (no flow on needle/seat).
The pressure at the regulator port should be less than 3 psi. Mine was 1.8 psi
Thinking about it. If the pressure is too high, it will push open the needle and seat at idle. And the regulator needs some margin to avoid fluctuation.