Fuel system line sizes question

[Mikes72]

I've just finished running new fuel lines on my 72 Challenger. Since it has a 440 I ran a 3/8 inch supply line. What I'm seeing is the fuel pump has 5/16 inch ports in/out as does the vapor separator and my Edelbrock carb has the 3/8 inlet port. Question is..... do I run all 5/16 fuel hose from the supply line up to the carb or some hogepodge combination of 5/16 and 3/8 hose? It seems odd that the vapor separator only comes with 5/16 ports but maybe after the pump it's fine because of the line pressure?

Appreciate any help here.
Mike

 

[Challenger RTA]

There is a 3/8" sending unit and a carter 3/8 high volume fuel pump.Don't recall were I got them.that's what I installed on mine. and a 3/8" fuel filter from napa I think. reducer 3/8" to 5/16" after fuel filter. I'll look and if I find the pump part number I'll posts it.I think the fuel filter was listed for Chrysler Cordoba.

Restoration Parts Source (RPS)​

Carter M6270 Mechanical Fuel Pump is for a LA block​

 

[themechanic]

5/16 will be fine unless you plan on doing a lot of wide open throttle driving.

 

[Mikes72]

Thanks for the responses guys. Since I'm really trying to get this beast running I'll probably start with 5/16 and see if I have any fuel starvation issues. Not planning a lot of WOT driving anyway.

 

[Challenger RTA]

A 3/8" to 5/16 barb fitting at the tank and fuel pump is what you need to get it running.3/8" and 5/16 hose to connect.

 

[Chryco Psycho]

I have run into starvation issues in the past , especially with 500 " stroker builds , I pay a lot of attn to the whole fuel system making sure everything is 3/8 id , I have drilled out the body of fuel pumps where the fittings enter & exit & opened up fittings as well , often the inside of the fittings will drop to 1/4 " , any restriction can hurt fuel flow .

 

[MoparCarGuy]

Remember that 3/8" fuel line tubing is 3/8" Outside Diameter (O.D.) which is approximately 5/16" Inside Diameter (I.D.). 3/8" fuel line hose is 3/8" I.D. which makes sense as it is meant to slip over 3/8" fuel line tubing and hose fittings. Many mechanical fuel pumps, even the Carter M6903 for the hemi, have 1/4" NPT ports as Chryco Psycho said.
Also, consider using fuel injection hose such as Vapor Guard which is not fuel-permeable along with the Vapor Guard fittings and clamps. Regular fuel line hose allows fuel vapor to transfer through the rubber (permeable) which tends to smell up your garage and cheap auto parts store fuel hose has to be replaced more frequently than high-quality fuel injection hose.

 

[FY1TopBanana]

try the 5/16 and see - rule of thumb for carbureted is 5/16 to 400 hp -- 3/8 runs out at about 500hp. This is based on WOT and 1/4 mile or more..
Many variables to consider but as Chryco says a big inch motor can quickly require fuel beyond the 3/8 line (and mechanical pump) limitations. The pump volume and pressure output are obviously a big part of the equation, as are fittings and filters. But even powerful pumps run into fluid flow restrictions that need more line cross-section. Its not hard to run 1/2 SS tubing in an E body. There are 1/2 inch pickup/sending units with 1/2 inch sock.
I cut the tube flares off the pickup and replaced with Swagelok tube-to-AN adapter. AN-8 is 1/2 inch equivalent but even in -8 fittings you can see the restriction.
I run an Edelbrock pump with 1/2 npt ports to a Fram post filter with 3/8 npt. 3/8 npt to -8 are common and the Fram ports are same size as -8 fitting passages. The pump requires an external regulator which I custom bracketed to the mech fuel pump blockoff plate. From there regular 2 separate -6 hardlines go to each AVS carb.
I also put a Swagelok union in the underseat area so the 1/2 SS main line can be installed removed as 2 pieces.

 

[frankb]

Use a 3/8 line. That will work with what you have and if you later go with more power then this will be one less thing to do. I run 3/8 pressure line on my 440/496 and have no fuel starvation issues.
Frank

 

[74stroker]

Did you run the 3/8 from tank to pump, or straight thru to carb? My engine was leaning out at WOT in 1/4 and I burned 3 pistons.
Engine builder replaced 5/16 sending unit and line with 3/8 from tank to mech pump. Does this make sense? It seems it should be 3/8 on thru to the carb! Any thoughts on this?

 

[Chryco Psycho]

you need 3/8 or bigger from the fuel tank to the carb , weather a mech pump will flow enough I am not sure , I used a electric pump