Confusion on Fuel Line I.D. and O.D

[66 Sat]

I've recently replaced my Holley carburetor with an Edelbrock and ended up with a fairly long piece of rubber fuel line from the pump to the carburetor. My small block car has 5/16" fuel line as opposed to 3/8".
My confusion arose with the inside diameter and outside diameter of these lines when I replaced the long rubber line with a section of hard line. The rubber fuel line is 5/16" Inside Diameter, which slips nicely over the hard line from the pump and also the fuel filter barbs which are 5/16" Outside Diameter. The Inside Diameter is only about 1/4".
Is this normal for these cars? Are the 5/16" lines measured as Outside Diameter?
As it stands now the diameter is changing 3 or 4 times, every time it transitions from hard to rubber line or from rubber line to fuel filter.
The car runs fine, I was just wondering.

 

[kiwigtx]

I believe the pipes are measured on OD.....which is unusual here for pipe work.

 

[Photon440]

I guess it depends on whether they consider the fuel line to be a pipe, or tubing.

 

[493 Mike]

Hose is measured by ID while tubing is measured by OD. Pipe is measured by ID, approximately.
Mike

 

[OKDart]

The supply line to the pump being larger is what matters most due to it being under suction. After the pump it's under pressure and the size can be smaller.

 

[gkent]

The supply line to the pump being larger is what matters most due to it being under suction. After the pump it's under pressure and the size can be smaller.

Schedule 40 or 80 “pipe” has a “nominal” i.d. - so for example a 2” pipe will be in the neighborhood of 2” I.d. On the other hand, a 2” “tube” will be 2” o.d. And will usually specify the “wall thickness” as opposed to the i.d.. As for fuel “line” … that’s anybody’s guess !!!

 

[Geoff 2]

Steel pipe such as brake or fuel line is measured in OD. Rubber hose [ fuel trans cooler, vac etc ] is measured in ID.

 

[RJRENTON]

I've recently replaced my Holley carburetor with an Edelbrock and ended up with a fairly long piece of rubber fuel line from the pump to the carburetor. My small block car has 5/16" fuel line as opposed to 3/8".
My confusion arose with the inside diameter and outside diameter of these lines when I replaced the long rubber line with a section of hard line. The rubber fuel line is 5/16" Inside Diameter, which slips nicely over the hard line from the pump and also the fuel filter barbs which are 5/16" Outside Diameter. The Inside Diameter is only about 1/4".
Is this normal for these cars? Are the 5/16" lines measured as Outside Diameter?
As it stands now the diameter is changing 3 or 4 times, every time it transitions from hard to rubber line or from rubber line to fuel filter.
The car runs fine, I was just wondering.
View attachment 1599002View attachment 1599004

Tubing is measured the I.D. X WALL THICKNESS.

Tube and Pipe are not the same. In simple terms, pipe is a vessel used to most often carry fluids and gas. Tube is used for structural projects like car frames and construction. Once you know what you want the next step is figuring out the size you need.

Tube is measured by an exact outside diameter (OD) and wall thickness.
Pipe is measured by a nominal outside diameter (also known as NPS or Nominal Pipe Size) and wall thickness.
Pipe Schedules & Weights

NPS is a North American set of standard sizes for pipes used for high or low pressures. The schedule number on a pipe relates to the thickness of the wall on the pipe. The higher the number, the thicker the wall. So Schedule 80 pipe is thicker walled material than Schedule 40 pipe. The Schedule number can be the same on two different sized pipes and yet the actual wall thickness will be different. For example a 1” Schedule 40 pipe has a wall thickness of .133”. Whereas a 2” Schedule 40 pipe has a wall thickness of .145”. So, the bottom line on pipe is that the Schedule number will increase the wall thickness, and the wall thickness changes based on the NPS

The dimensions provided for tubing refer to the actual outside diameter. In other words, the actual physical OD of a tube is just the same as it's nominal OD. The size of a tube will keep the same OD no matter what the wall thickness is. For example, the actual outside diameter of 1¼″ pipe is 1.625″ - while 1¼″ tube has a true 1.25″ outside diameter.

Consequently, both the size of tube and pipe is measured by it's OD and the thickness.
This should clear up ghe confusion......
BOB RENTON
https://www.industrialmetalsupply.com/metal-resources/metal-faqs

 

[66 Sat]

Thanks Bob, but my confusion is more along the lines of "is my fuel line size adequate" and "it would seem to depend on what type of line I'm using".
I've read that 3/8" line is required to support a certain amount horsepower. I've got what I thought was 5/16" line throughout but now realise the actual I.D. of the line varies dramatically as the fuel travels along its course and is only 5/16" I.D. on the rubber hose parts. The hard line is smaller than that (I.D.).
The 3/8" line would have the same issue, but each diameter would be bigger throughout.

 

[Geoff 2]

66 Sat.
I remember you stated previously that you had the car on a dyno. From that you can estimate the engine's hp. As a rule of thumb: 25 US gals is reqd per 300hp & part thereof. This assumes correct A/F ratio. A safety factor needs to be factored in & you will get lots of examples..... I think 30% is enough, ie the fuel pump needs to deliver the calculated amount of fuel + 30% to the carb inlet. Very easy to measure with an electric pump, not easy with mech pump.
You will probably find some flow figures for 5/16 & 3/8 tube on line.