Fuel injection return line

[Dirtracer 619]

I currently have -8 fuel line to the second filter and -6 to the rails and -6 for the return line
So now it's time to replace the return line should I go to -8 or just stay -6. Does it even matter???
I have to replace it any way so just wonder if an upgrade might be needed

Thanks all

 

[Bert is my name]

If you use the same size lines and fittings you will have spare parts already on the car in the event of a failure. Carry some a.n. caps with you.

 

[partybarge_pilot]

Return line always needs to be larger than the supply line. This will let the regulator do it's job properly.

 

[JP_JCM]

Return line should always be the same size, if not 1 size larger than your feed line.

 

[Crusty Shellback]

HMM!
on my Holley Sniper EFI, my return line is the same size as the supply. The regulator is built into the sniper unit. The return only sees about 5 PSI of fuel flow. So no reason for it to be bigger. If your regulator is in the EFI unit and not back at the tank, then there should be no need for a larger return line as there should be minimum flow/pressure in the line.

 

[cjohnson]

Fuel systems are complex and the return size does matter. If the system is working fine and performing as desired but deteriorated parts need to be replaced the safest bet is to replace them with the same size parts. Going bigger on the return wouldn't help anything and would cost more money, add weight(minimal), and possible make routing the return more difficult. If the system is not working then it should be diagnosed and/or redesigned.

 

[jon coleman]

Yup ,^^^psi& flo are two different things, i can have 50 psi but if im pushing it thru a pinhole i wont get the flo rate required, still got50 psi, a return line in theory only needs to be big enough to Flo the fuel back with out excessive restriction( pinhole), also, this is if return line is After regulator.also save some cash, a 0 psi line can be a standard fuel line , i had that on my efi, then i ran it thru some really tuff , flexible conduit for crash protection.

 

[JP_JCM]

depending upon your pump and regulator, a return line larger than the feed can be necessary. you want absolutely no restriction in the return at all. this helps dampen the pulses in the fuel rail.

 

[Bert is my name]

Return size is a function of supply. Yes you want flow without restrictions. But , I have yet to see a factory return line be larger than supply. The engine should be consuming fuel. Correct? That leaves to reason that for a given supply there should be the same return if not less.

In diagnosing a fuel problem I will close off the return. In most cases the engine loves the extra fuel. So I don't get small supply and sewer drain return. Hasn't been my experience in 20 plus years of building cars.

 

[Bert is my name]

Thus. My original post of same size fittings and lines.

 

[Bert is my name]

Most fuel injected engines like high pressures

 

[Bert is my name]

T.b.i. injected Chevys run great at 20 p.s.i.
Factory is 12.

Vortech engines run at 35 to 40 .
50 makes power.

Dead head the supply side of the pump. Start decreasing pressure until it runs like poop.

 

[partybarge_pilot]

Dead heading a large electric pump is a good way to burn it up. It will also greatly increase your chances of boiling the fuel in the line.

 

[cjohnson]

Return size is a function of supply. Yes you want flow without restrictions. But , I have yet to see a factory return line be larger than supply. The engine should be consuming fuel. Correct? That leaves to reason that for a given supply there should be the same return if not less.

In diagnosing a fuel problem I will close off the return. In most cases the engine loves the extra fuel. So I don't get small supply and sewer drain return. Hasn't been my experience in 20 plus years of building cars.

May or may not be factory. The engine does consume fuel. But not the same amount all the time. The reason for a larger return, in some cases, is for big HP engines. They consume a large amount of fuel at WOT. When the throttle is cut the high pressure/high volume pumps can overwhelm the return if it's not sized correctly. The amount of fuel the engine uses at idle may not be enough coupled with a return line sized the same as the supply to handle the volume from the fuel pump pushing fuel at 80-120 psi.

 

[JP_JCM]

^^^^^^^^^^^^^^^^^^ this right here.........

 

[dzrt performance]

first of all...size ALWAYS matters

chances are if what you had was working then no reason to change anything.

the issue of what size to lines to run can not be answered without more info. specifically what size/flow pump, injector flow, fuel flow demand of the engine and so forth.