Technical Fuel line size

Getting ready to do the fuel line in a 1941 ford pickup. New Drake gas tank. New Blueprint cruiser 350 crate engine. The tank has a quarter inch line. The Holley carb has a 5/16 barb. I have read that 3/8 is the way to go but this engine was dyno’d with this carb. Adapt the 1/4 line right out of the tank to 5/16 and run it the the pump, then 5/16 out to the carb? I can’t see why running 3/8 to the pump, then going down to 5/16 to the carb would be beneficial. Thoughts?

 

I’ve used 5/16 and 3/8 for fuel line

If you have 1/4 out of the tank going bigger to the pump won’t really help , keep it 1/4 then run whatever size out of the pump to the carb that fits correctly

 

Is the tank fitting interchangeable?

 

3/8" is the defacto standard

 

Here's what I did with my new Drake in my 39. There's a ⅜ pickup line below the ¼" fitting inside the tank. You can see it about 2 or 3 o'clock in the opening:

I drilled the ¼" hole in the bottom of the fitting to just over 5/16ths and cleaned up the tapered seal area with an appropriate drill size, and had the bit wrapped in masking tape to avoid mullering the threads:

I used a 5/16ths tube nut and compression ferrule on a steel line:

I leak tested with about 10psi give or take and some soap suds. Leak free and 5/16ths pickup from the tank. Too fkn easy...

I'm positive it would be enough pickup for even a mild big block in a small early Ford. Anything wild would have a dedicated custom fuel system, no?

 

^^^^^ Agree, 5/16” will serve just fine and simplifies the rest of the install.

 

Major correction on the initial drilling. I used a 5/16" steel line on a tube nut as the 1st drill guide. Sorry I forgot to mention that. I did the cleanup with a taped bit to make sure the seat was smooth. Sorry I forgot to share that...

 

It ALL...depends on the engine power !!!

A stock flat head 6 will do fine with 1/4" dia. line.
A mild 350 inch (30hp or less) or less can get away with 5/16" dia line.
A hot rod (350hp or so) can use 3/8" dia. line.
A hot rod/race engine over 400hp should use 1/2" dia.

These diameters should be considered, from the gas tank to the regulator / front of car. The combination of carburetors will determine the size from the regulator / line splitter. I'd consider 5/16" dia. to be the minimum from the splitter / regulator to the carburetor(s).

If your engine is somewhere in between the above...pick a diameter...between the same lines !

You CAN...find recommendations on fuel line diameters in the...net !

Mike

 

I run 3/8" fuel lines. That's 3/8" from the tank to the carb.

Heck, even my 1981 Buick Regal (G-body) that came with a normally aspirated V6/T350 (now it has a 350 cube) came with 3/8" lines from the factory.

1/4" might be fine if you're running a Briggs & Stratton 3.5hp and even that might be pushing it

 

Lets say it's December of 1965, as an example, the fuel line for a 327/275hp Nova came from Chevrolet with a 5/16 fuel line and the 327/350 hp cars had a 3/8" line.

 

Personally I'd run 3/8 all the way if I wanted 300 HP performance without problems. Now's the time.

 

This fuel line size question seems to pop up a lot. Most folks can just copy a factory application similar to theirs and be just fine. There are more technical and mathematical ways to calculate the proper line/hose and fitting sizes. For those that like to digest this stuff here is some food for thought taken out of an old Russel catalog. These charts are very useful when designing a fuel system and will confirm whether or not your in the ball park.

 

Run 3/8" from the tank to engine but keep the 1/4" in place to run a return line back to the tank to eliminate vapourization.

 

Yes!

 

Smokey used 2" diameter fuel line.

 

Probably hiding nitrous inside of it too!

 

Over the years I've built all my cars using 3/8 bright annealed stainless tube. East to bend, never any corrosion problems. I have found some lately on e-bay, reasonable price and they'll ship 8 ft length.

 

I use 3/8" on my cars. Even if it has a smaller engine. Then if I change to a bigger engine later it's one less thing to change.

 

I agree, I've never built anything without atleast 3/8" line to the mechanical fuel pump (if I didn't go electric).

If I went electric I went with 3/8" up to the motor, then if space was limited, when I went to hose to go from frame to motor I'd downsize there to 1/4" or if space wasn't a problem back to 3/8" steel line.

On any thing built with some HP and 400 Cid or bigger got 1/2" to the motor then down to 3/8" on the motor....

Never heard anyone complain about the fuel line being too big, just extra storage !!

..

 

I thought this was how to best use a Drake tank and feed a mild SBC. My bad...

 

I would figure out how to get 3/8's out of that tank, I thought they offered the tank with a 3/8 line as an option, I don't know why you would want to starve the fuel pump with 1/4 inch line.
You wouldn't want to drink your favorite 44 oz soft drink through a coffee stir stick would ya ???

 

My car starves north of 5500 RPMs. I have a 5/16" fuel line back to the tank. A bigger line would be better, add it to the list...

 

I like @theHIGHLANDER post. Simplest way to get a consistent diameter front to back with minimal adapters. I have 5/16 on the street 351W in my 47.

 

You can spend a lot of time chasing a poor performance problem when you don't know what the root cause is. With the smaller line there is always the chance that it may affect performance.........with the larger line you know its not going to be a problem. I'd rather take care of it during installation than have to fix it later if there is a problem.

 

Our funny car had a 1" feed line. It didn't starve for fuel either. Then again how many big fkn Cadillacs and Buicks and Olds had a 5/16? Full size Ford models? Ford trucks?
Hey @olskool34 tell us about this fire breather you're dropping in there. What, .750 roller cam, 12.75:1 compression? Holley 1050 Dominator? Or is it just a little upscale 350 ready to pull a feather of an early V8 down the road? Gasoline is .5 lbs fuel per HP hour. I think you can FLOOD a 350HP small block of any variety with a 5/16 line. Jeezuz kids, it's not a fuckin pro mod. WTF. Or maybe my solution to my future small block plans was truly too easy. Next week, oval tires that last longer and give better mileage...

 

As I stated earlier, GM installed 3/8" fuel line in a gutless, carbed 3.8 cube (no turbo) '81 Buick Regal. Not exactly a fire breather in anyone's eyes but, I guess they could have made a mistake

 

^^^^^ GM’s one item fit’s all mentallity at work.

 

What do you think is the downside of that?

 

Or, they just used 1 fuel line in every version of that car to simplify production. Some were TBI, yes? More pressure and volume req'd. Did your 3.8 need it? Fuck no, and I'd bet a good cup of coffee it also had a return to the tank. Most did and still do.
I love this place, but sometimes something as simple as an amp setting for a TIG weld gets all moldy with potential dangers to time and space continuum as studied by Albert Einstein. Simple is fast, easy, cheap, more than enough, gets you done sooner with zero negative effect on the end result. And I'm quite familiar with pressure, volume, HP requirements, etc. This ain't that. A fellow rodder with a new repop tank wants a simple solution to feed a mild SBC. I'm done, tip your waitress on the way out...

 

For GM less inventory. For a non turbo nothing.