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View Full Version : Fuel Lines-Why is the return line smaller?

BBShark
07-01-2008, 06:41 AM
What is the reason for making the return line smaller diameter than the supply? I am using a 3/8 supply line and see that most manufactures use a 5/16 return. Well, I can't find much in the way of -5 AN fittings (5/16) and would like to use -6 AN (3/8) supply and -6 AN return.

Am I missing something? Any reason why this will not work?
camcojb
07-01-2008, 07:28 AM
What is the reason for making the return line smaller diameter than the supply? I am using a 3/8 supply line and see that most manufactures use a 5/16 return. Well, I can't find much in the way of -5 AN fittings (5/16) and would like to use -6 AN (3/8) supply and -6 AN return.

Am I missing something? Any reason why this will not work?

should be fine. The only time you have an issue is if the return line is too small to handle the amount of fuel bypassed, and causes the fuel pressure to rise due to the restriction in the return line. If you're running a large race type pump you may need a #8 return, but the #6 should work in most all cases.

Jody
badmatt
07-01-2008, 07:45 AM
should be fine. The only time you have an issue is if the return line is too small to handle the amount of fuel bypassed, and causes the fuel pressure to rise due to the restriction in the return line. If you're running a large race type pump you may need a #8 return, but the #6 should work in most all cases.

Jody

hehe so jody for my -12 feed you think i need a -10 return? lol
Musclerodz
07-01-2008, 07:54 AM
Return line is smaller because it is only returning unused fuel from the carb or EFI. The larger line will be fine.
camcojb
07-01-2008, 08:07 AM
hehe so jody for my -12 feed you think i need a -10 return? lol

I've never needed larger than a #8 return, but I've never run a #12 feed either................. :wow:
badmatt
07-01-2008, 09:10 AM
I've never needed larger than a #8 return, but I've never run a #12 feed either................. :wow:

hehe yeah the -12 is a bit large but its what I need.
XcYZ
07-01-2008, 10:40 AM
Damn. How much fuel pressure?
camcojb
07-01-2008, 10:41 AM
Damn. How much fuel pressure?

and how much hp?

Jody
BBC69Camaro
07-01-2008, 12:31 PM
I think it depends on the Fuel Pump manufacturer. I would run what they recommend. I know for BG they want a -8 an feed and -10 AN *return* (for BG220HR) while a comparative Aeromotive Street Rod pump wants a -8 an feed and return.
badmatt
07-01-2008, 02:07 PM
and how much hp?

Jody

shooting for 1600-1800hp

65PSI is what im thinking ill be around
Ruslow
07-17-2008, 07:50 PM
Also keep in mind taht the return line is so to speak a gravity feed back to the tank.The only psi it has on it is the amount of fuel is that is being let past the fuel reg.so keep the shaper bends out of it and try for more of a drop to the tank than an increase in height.Stan