5/16 fuel lines....big enough?
#1213745
04/10/12 06:39 PM
04/10/12 06:39 PM
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Joined: Jun 2010
Posts: 1,144
wellington ohio
68-scatpack-rt
OP
In thin ice
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OP
In thin ice
Joined: Jun 2010
Posts: 1,144
wellington ohio
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hello all. i'm going to replace all my, cobbled together, fuel lines on my 68 coronet rtr. it has the factory avs and a stock 440hp.
i'm going to use some prebent reproduction lines and i'm wondering if the 5/16" are fine or should i go to a 3/8" main line?
thanks, rob
unions....the folks who brought you the weekend!
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Re: 5/16 fuel lines....big enough?
[Re: Mr.Yuck]
#1213753
04/10/12 10:32 PM
04/10/12 10:32 PM
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Joined: Feb 2003
Posts: 18,582
Rust Belt, SW PA
Silver70
I Live Here
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I Live Here
Joined: Feb 2003
Posts: 18,582
Rust Belt, SW PA
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If I replace mine I always go 3/8. My 68 satellite with a 318 even has 3/8 now in stainless. Not that I had planned to build it up, but you never know.
68 Road Runner, 69 Belvedere, 71 Challenger Vert
340 barracuda, 01 Ram CTD, 95 Ram, 04 Ram, 85 Daytona turbo Z
66 GTO, 06 Magnum RT AWD. 07 Ram CTD, 07 Ram
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Re: 5/16 fuel lines....big enough?
[Re: DANA60]
#1213756
04/11/12 01:36 AM
04/11/12 01:36 AM
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Joined: Jan 2003
Posts: 5,875
communist bloc of new jersey
jamesc
master
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master
Joined: Jan 2003
Posts: 5,875
communist bloc of new jersey
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Quote:
11.18 @ 123, 1.51 60', fast68plymouth, 68 Satellite, 383, stock 906's, 3550lbs
afaik the above car was running a stock 5/16" fuel system with a carter HV mechanical pump...so the answer to the title question is yes.
if it's not a hassle and much more money over the 5/16" i see no reason to not use the 3/8 but i think it's safe to say it's not necessary at all 
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Re: 5/16 fuel lines....big enough?
[Re: Jjs72D]
#1213761
04/11/12 10:57 AM
04/11/12 10:57 AM
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Joined: Jan 2003
Posts: 5,875
communist bloc of new jersey
jamesc
master
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master
Joined: Jan 2003
Posts: 5,875
communist bloc of new jersey
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Quote:
Isn't this a case where the chain is only as strong as its weakest link?
no it isn't
fluid flow is caused by pressure differential, it flows from an area of higher pressure to an area of lower pressure.
first a basic understanding about gauges and atmospheric pressure
PSIG is Pounds Per Square Inch Gauge which is what most gauges we see are. what this means is that the gauge reads 0# at atmospheric pressure.
atmospheric pressure is normally about 14.7 PSIA (caused by the weight of our atmosphere), which is Pounds Per Square Inch Absolute. a PSIA gauge will read 14.7# at atmospheric pressure (whereas a PSIG sitting next to it will read 0).
take a 1" pipe a mile long and put a pump at the beginning of it and leave it open at the other end, then put accurate PSIA gauges every ten feet. start the pump, what you will find is that EVERY gauge from the pump to the open end reads continuously lower. the gauge at the open end will read 14.7#. pressure at the pump will be highest, pressure at the open end will be lowest.
take the same setup only put the pump at the other end so the mile long pipe is on the suction of the pump, put the open end in a pool of water. then start the pump and what you find is that EVERY gauge from the open end (at the pool) to the pump will read continuously lower. the gauge at the pool will read 14.7 PSIA and every other gauge will read lower, the gauge at the suction of the pump will have the lowest reading of all of the gauges.
it doesn't matter what you're pumping, or how big the diameter or length of pipe the principal is the same.
in a sense technically there is no such thing as a vacuum only an absence of pressure. under most common standard conditions the majority of pumps we deal with on a daily basis will have no more than 14.7 PSIA available to "push" the liquid into them so they can pump it. make no mistake about it liquid is "pushed" into a fuel pump.
most pumps have a larger suction as opposed to discharge to reduce the losses on the suction side. IF the NPSH (net positive suction head) drops below the pumping requirements under the conditions the pump is operating the fluid will flash to a vapor, the pump will cavitate and cease pumping. NPSH is affected by many things such as viscosity, temperature, flow rate, vapor pressure etc.
so in this case just because the dimensions at the pump and carb are 5/16 this doesn't mean the 3/8" upstream can't or won't be beneficial.
these aren't my opinions these are facts
that said the 5/16" will do everything the OP needs.
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Re: 5/16 fuel lines....big enough?
[Re: Mr.Yuck]
#1213763
04/11/12 01:15 PM
04/11/12 01:15 PM
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Joined: Jan 2003
Posts: 5,912
Athens, Greece
Pyper70
master
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master
Joined: Jan 2003
Posts: 5,912
Athens, Greece
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I run 5/16" from the tank to the pump....3/8" from the pump to the prefilter. I run two 500cfm edelbrocks...and a 120GPH Eddy Pump...no issues at all
Family owned 1969 Charger R/T DualQuad 440/727/GVO/3.55s
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OP, go with the biggest one you can buy that will fit like the stock ones do, replace the pick up inside the tank with a 3/8 also 
