Technical bumping up the fuel line size at the gas tank

The fuel tank for my 47 Ford has the 1/4" line coming out of the tank. Someone had suggested drilling out the threaded fitting to fit 3/8" line and run it to the inside of the tank.
Would I just drill the flange to the same size and pull out the original line?

 

Why? I’d just leave it as is; increasing just the diameter of the tank pickup isn’t going to be of any benefit.

 

It totally depends on what you’re looking looking to feed, if you have a hopped up small block under the hood I would recommend increasing the pickup size from 1/4” to 3/8”.
But if you’re still running a stock setup 1/4” will probably do the job.

 

-I've been trying to figure out what would work best. I asked a couple of people and you get totally different answers

-351w 4bbl
I'll more than likely keep it stock.
Could I put a 3/8" adapter right at the tank with out any issues?

 

It's not just the increase in line size that will make a difference in fuel delivery, fitting design,(especially elbows) makes a difference, some styles are more restrictive than others, probably not a big deal for daily driver type cars but higher hp cars will appreciate a better flowing fuel system.

 

A fuel system is only going to flow what the smallest orifice or tube or hose or fitting in the system flows.
Meaning, that even if you run a 3/8 line from the tank to the fuel pump, if you don't change the pickup tube inside the tank it is only going to flow what a 1/4 inch line will flow.

 

True there, When I bought the 57 Chevy panel with a built 327 with the early Corvette dual 4 barrel intake and carbs the guy who assembled it put a brass fitting for a natural gas line in the connection set up for the carbs. It would cruise down the highway fine but try for hard acceleration from a stop and it would run out of gas before you ran out of gear, shift to second and it would pull until it ran out of gas and you shifted again. the fuel pump would refill the float bowls when you shifted but the 1/8 orifice in the fitting restricted the fuel like crazy.

 

It's been a while since I put mine (47 Ford coupe) together, but I just used an adapter fitting at the tank to run 5/16 steel line to the front. Been running same 351W with mild cam and 4 bbl, with no fuel issues for 47ooo miles.

 

A fresh straight 1/4" line with few bends will go a long way in making run better. The factory line could be restrictive due to internal rust and sharper bends then what is actually needed..

 

If you are ever going to run this thing hard, that 1/4" line will be a problem. At least 5/16" from the fuel to the carb....all the way...and no paper filters on the suction side.

 

I'm using a 5/16 line to match the fuel pickup in the '68 M- - - - - - tank that I put in my '29 Model AA. Not sure what filter to install and if it should be between the fuel pump and carburetor or inline along the frame just before it connects to the fuel pump. I need to put a short piece of hose there anyway to dampen stress on the tubing from vibration. Thought I might use the same one that's on my '96 Explorer, maybe get the bracket from the local pickparts. Any recommendations or guidance?

 

IF you have to up size the line and don't want to buy a custom tank, I see a few ways.

1. Cap off the stock pickup, install a larger tube into the sending unit area (90 at top and bottom) with a screen on the end.
2. Clean out/air out tank, cut out old fitting/pick up and braze/weld in larger fitting/pick up.
3.Cut out some of the trunk floor and use a Mustang tank.

 

One factor that is often overlooked is the vent for the tank, fuel can only get out if atmospheric air can get in. Also matters where the pump is. If on the engine you will get resistance in the long length, less so when more of it is pushed. JW

 

One thing to always remember,

As pipe diameter increases for the same flow needed at the end, the velocity in the pipe decreases. Slow moving fuel in lines under cars can be a cause of vapor lock and heat soak. Just saying. Its like some folks running 3/8 or 1/2" line on a 4 banger pushing 40 hp.

Now on gravity feed lines, yes the velocity decreases but the flow increases as pressure is gravity only. The main opposition to flow is the fluid itself and bends and lengths. This is why I was able to fuel a stock model A gas tank on 2 downdraft carbs without issue of starvation.

On your project, if you wanted to, up the line to 5/16" line, leave the 1/4" fitting on tank will be a point of faster velocity but should still flow well. I dont see any reason for upping the line size any more than this unless your looking at 400 hp or more. 5/16" line is my normal go to for mild builds.

 

Just a side note, when you increase the diameter of a tube by on 1" to 2" the amount out of flow is increased by 4.

 

I had a 40 Ford feeding a healthy 350 and I left the stock pickup in the tank, ran fine.

 

Topher,

I do believe that Ford used 3/8 fuel lines in vehicles equipped with 351W. Just seems that the factory size would be the goal? If you know what vehicle your 351 came out of maybe just use that a reference as to what is needed. No need to guess or try to reengineer something that was figured out long ago.

 

I’m using the stock 1/4” pickup on mine. It comes out of the tank, a piece of rubber hose connects that to a fuel filter that has stepped tubes, then another short rubber 3/8”hose to the electric fuel pump, from there 3/8” metal to the carb. All in all, probably no more than 3-4” of 1/4” line right at the tank. The 302 and the 350 before that never starved for fuel no matter how fast I went.

 

Changed both the pickup tube to 3/8 and the fuel line to 3/8 on a on a 48 that I sold a few years ago.
Drilled a 3/8 hole in the gas gauge sending unit plate and tacked in a 3/8 pick up tube, if you're changing the fuel line might as well go 3/8

 

That can't be a Ford, look at those hubcaps!

 

Increased the fuel pickup in my big block wagon. Went from 5/16" to 3/8" to help supply 600+HP. Worked out well and took a couple hours to do. I do need to tweak the float arm a little to get empty on empty.

 

I put 3/8" line on anything I build, even with a small engine. It has saved me a few times redoing the lines when plans change and a bigger engine goes in later.

 

It's easier to address the question/problem beforehand than to find out later that you need to do something. Also, new fuel lines are a good practice on any old car build. You never know what the inside of the old lines looks like, and if you replace them, you might as well increase the size. You need to check the inside of the tank first to make sure its not in bad shape.

 

5/16” can feed a dual quad engine which is the minimum I would install but you need it into the tank.

 

Let it be. The stock 1/4 inch line will work just fine.

 

Common sense is a wonderful thing.

 

If you are worried about fuel flow capability, plug the stock tank fitting and put a new pick-up tube in the top of the tank.

 

1/4" seems strange to me. My 49 Dodge with a 95hp flathead 6 has a 5/16" line from end to end factory. ..... Sooo, 1/4" just sounds small .... carry on.

 

It’s a little funny that every tank fuel line Ive replaced in the last forty years has been 1/2”. The Fairlane has a return line that is 1/2” also.

 

I have the stock 1/4 line from the tank to all 5/16 after maybe 3 inches is 1/4 and I have a 350-375 hp 350 with no issues.. it's the tape in the fuel pickup that's the issue