Technical installing fuel lines for the masses

When I started in the automotive trade, a lot years ago, we were told inspectors allow no copper brake lines, not because work hardens etc, but because it to easy for someone to cheap out and by thin wall, seamed copper pipe, which on visual inspection is hard to tell if it is substandard.

 

Yes, I'm using the plain black from fuel pump to dual feeds on my '39 in my avatar. Didn't show it here as not sure they're HAMB friendly. But I really like tis system, and they were easy to assemble, and seal great.

 

I like the black braided line and black fittings my self, I use hard line for the run but connect tank to the fuel pump and the bulkhead connection at the engine compartment to the engine with the braided black lines. I plan on trying many different combinations under the hood and doing it this way will give me the most flexibility. I’m trying to complying with the NHRA rules that say only 12” of rubber hoses total unless it’s braided and I’m using a return regulator.

 

A little information that may help.

There are different thread systems but since you are from Missouri, you most likely are interested in the American stuff. What follows is a simplistic explanation, so please don't expect it to be perfect or all inclusive.

With American Standard bolts and nuts you basically have a new size predicated on 1/16 of an inch. So you have
4/16 (1/4) .........5/16........6/16(3/8)........7/16.......8/16 (1/2) and on and on. Sizes smaller than 1/4 don't follow that pecking order, but for ease of explanation we won't worry about them for now.

So bolts and nuts also have two basic thread forms or "pitches". Pitch is how far a nut will move if rotated one turn.
If you have a 16 Pitch thread, one rotatation will move 1/16 inch. If you have a 12 pitch, one rotation will move 1/12". If you have a 32 pitch, one rotation will move 1/32".

For each size thread there are normally 2 thread pitch choices. With a 1/4" bolt we have a choice of 1/4-20 OR 1/4-28. One is a "fine thread and one is a coarse thread which just means one has more threads per inch while the other has fewer threads per inch. So......1/4-20-UNC.oarse................1/4-28-UNF.ine

When you move to pipe threads, its a little less obvious. A 1/4" pipe thread is much larger than 1/4". The 1/4" refers to the size of the hole in the pipe....the inside diameter. They also come in "straight threads" and "tapered threads"

When you get to the AN thread system, this stands for ArmyNavy. It was a system established by the government to use in the military but has found favor in private industry. There is another spin off called JIC that is used on industrial equipment and while supposedly doesn't meet the same specs as the government stuff.....its still quality stuff and usually cheaper. Its made from steel instead of aluminum.

The thread system for the AN type of fittings mirrors the FINE thread pitch and size of nuts and bolts NOT the thread sizes used on common pipe thread components.

So realize that that AN is also structured on a 1/16 basis both on the threads they use and the size of the tubing.
By that I mean that a 6AN fitting means that its for a tube with an external diameter of 6/16(3/8). An 8AN would be 8/16 (1/2) Thats the tubing size. There will also be an external thread on the fitting and its thread pitch will be the same as the Bolts and nuts we commonly use..........but they will be the "fine" thread. Now thats not to suggest that that we want to screw nuts and bolts onto AN fittings, but to point out the fact that they are NOT pipe fitting threads.

 

One important hotrodding exception.

7/16" "coarse" thread is 14 TPI, whilst "fine" is 20. There is a third thread "extra fine" at 28TPI.
i.e. 7/16-14 UNC, 7/16-20 UNF and 7/16-28 UNEF.

Of course, Alfred Stromberg did something a little different. The "special" inlet thread on a Stromberg is 24 TPI.
i.e. 7/16-24 UNS.

Cheers,
Harv

 

Ekimneirbo - GREAT POST!

Lots of early carbs use pipe fittings. Because I could never visualize the sizes, I finally bought male and female fittings of all sizes, and labeled them. Quite easy to figure out the pipe size when one has samples.

Jon