TheSamba.com :: View topic - Putting AN fittings on ends of the hard fuel line

Sat Jan 13, 2024 9:54 am

Can I add a stainless steel tube sleeve, tube nut and a 37 degree flare on the ends of the hard fuel line so I can run AN fittings w/ flexible lines. I don't like clamps as much as fittings.

And 1/4" being the closest diameter for our fuel lines, that translates to -4 AN.
Is that ok to run from tank to tunnel, etc. or should I add a fitting to the 4an tube nut to change it to 6an fittings and lines?

Sat Jan 13, 2024 10:04 am

FYI, the factory didn't use clamps, the pressure is so low, they weren't needed.

Two reasons to use AN fittings on the fuel supply:
1) You are using high pressure as in fuel injection.
2) You have money to waste and you like the bling.

The 2-3psi from the stock mechanical fuel pump will not cause the German fabric covered line to come off. Adding a ABA style band clamp is extra protection if you want. It's belt and suspenders.

Sat Jan 13, 2024 10:10 am

good feedback Glenn, thank you.

Sat Jan 13, 2024 11:51 am

While I don't disagree with anything Glenn posted above, I have looked into terminating the tunnel hard lines in AN fittings. If this is something you are intent on doing... here is a video that covers a few options for terminating tubing with AN fittings. It presumes you have SAE size steel tubing and may not work with the OE metric tubing. You may have to source AN fittings that work with metric tubing.

The compression fitting is the easiest as you just need a set of wrenches once the lines are cut to the proper length. No need to deal with a flare tool and getting the correct flare on the end of the tubing. But if you plan to use the stock metric hard lines maybe the flared tubing option is the better one as the seal will be made to the tubing material which has been flared and not depending on the crush of the incorrect 1/4" ferrel being installed on a 5mm tube.

While I agree that the correct size hose for 5.5mm/0.25" tubing should be -4 AN fittings as this is the equivalent of 4/16 = 0.25"... the actual ID of the -4 AN fitting would be closer to 0.17" which means you are adding a restriction in the overall flow by going with -4 AN fittings.
Also, you may find it difficult to source the needed -4 AN fitting/adapters you need. I found it easier to source -6 AN compression fittings that would attach to the end of 0.25 OD tubing than to find -4 AN compression fittings for 1/4" tubing. -6 AN hardware is a much more common size for both fittings, adapters and hoses when it comes to automotive use.

So out of convenience you may want to look at -6 AN hardware.

Sat Jan 13, 2024 1:30 pm

On my 2275cc, bling bling 💎

Sat Jan 13, 2024 1:41 pm

richparker wrote: On my 2275cc, bling bling 💎

I still see clamps ;)

Sat Jan 13, 2024 1:53 pm

Some bling on this pile too. The local race tracks frown on more than 12" total of rubber fuel line here.

EDIT: I used a -6an adapter fitting on the hard line at the frame horn connection.

Sat Jan 13, 2024 1:57 pm

One argument for AN fittings, is that after a few months, it is often impossible to get fuel lines back off of a barbed fitting. I'm assuming it is the current fuels that dry and harden the hoses, but I almost always have to cut them off of a barb. With a JIC or AN connection it's just two wrenches and apart. Of course this doesn't do anything for a stock pump or carb..

Sat Jan 13, 2024 1:59 pm

I only have a few inches of hose. I use stainless hardline like it came from the factory.

ABA Band hose clamps.

Sat Jan 13, 2024 2:45 pm

Glenn wrote: richparker wrote: On my 2275cc, bling bling 💎

I still see clamps ;)

Yea, clamps on the 2 short sections of FI hose. 🤷‍♂️

Sat Jan 13, 2024 8:56 pm

I totally disagree with Glen on bling and extra wasted money. If there’s any system that was under-engineered, it was the fuel system. I really don’t know if it’s the modern ethanol fuel, or the “rubber” currently available, but fuel leaks and engine fires have been a problem for air cooled for as long as I can remember. If there’s anywhere that money isn’t wasted, it’s on fuel system upgrades and fire extinguishers.

I think it’s a wise move to eliminate any clamped joints in the fuel system - under the tank isn’t a big deal, but anything aft of it would benefit. A braided teflon tubing would be ok in the engine bay as long as it isn’t subject to significant flexing over its life. I would not use any rubber or Teflon over the heat exchanger; that needs to be metal tubing, preferably with a short length of silicone and fiberglass heat sleeve crossing the exchanger. I can’t think of any downsides to using a threaded connection anywhere in the fuel system.

Sat Jan 13, 2024 8:59 pm

Use hose that is ethanol safe.

Sun Jan 14, 2024 5:28 pm

67rustavenger wrote: Some bling on this pile too. The local race tracks frown on more than 12" total of rubber fuel line here.

EDIT: I used a -6an adapter fitting on the hard line at the frame horn connection.

precisely what did you do? a compression fitting? a tube nut and sleeve? aluminum ok or stainless steel only?

I can find a tube nut and sleeve for a 1/4 hard line but it only adapts to a 4 AN female... so I think I'll have to get a 4an male to 6an male to make my plumbing 6an

Sun Jan 14, 2024 6:23 pm

Mine's not running yet, but here's how I set my fuel line up. I've got a 4AN straight bulkhead fitting at the front under the tank, and I flared the line coming out of the frame horn for a 4AN standard tube nut and sleeve. I'm using aluminum fittings but in this scenario I don't think it matters that much steel vs. aluminum. I may see some ethanol corrosion on the aluminum down the road so that's something I'll have to check in the future.
I'll run the frame horn line to the left hand body sheetmetal right beside the engine, to a bulkhead fitting. There is no real benefit to putting 6AN tubing on a stock engine; it's easier to keep everything the same to avoid adapter unions with their extra potential leak points.

Keep in mind most braided hoses are rubber, and you're not guaranteed a high quality rubber if you buy based on price. As Glen says, make sure your rubber is rated for ethanol. Otherwise you can get a teflon braided hose, but teflon does take a set over time and can crack if it's flexed much after it takes a set. I don't see a problem with either material for our fuel lines, as there is no flexing anywhere.. just vibration.

Sun Jan 14, 2024 6:28 pm

For An fittings, I d stick with the correct sized tubing, You might find on the interweb what the tolerance is for 1/4 tube to work with AN fittings, and if the metric VW fuel lines is within those limits then go for it, but otherwise it maybe problematic to use an AN fitting for 1/4 inch on a non 1/4 inch tube. If you want AN, you can run a whole new tube of the correct diameter. Keep in mind that vibration isolation maybe needed at the engine to chassis connection area.

Sun Jan 14, 2024 6:53 pm

You can easily see how well the tubing matches up against a fitting once you flare it. There is more than enough allowance at the fitting interface to make up for differences in wall thickness that I wouldn't sweat it here at all

Sun Jan 14, 2024 6:57 pm

scrivyscriv wrote: There is no real benefit to putting 6AN tubing on a stock engine; it's easier to keep everything the same to avoid adapter unions with their extra potential leak points.
6AN is a more common size for fuel components, 4AN less so. My suggestion for 6AN was not so much for need of a larger ID but more for availability of components.

I just did a quick search on the Summit Racing's site for 4AN sized inline fuel filters. Many brands offer inline fuel filters with 6AN, 8AN, 10AN fittings, but they only have 3 brands of fuel filters with native male 4AN fittings. This suggests less support for 4AN fuel systems, making it a bit harder to find components... or the need to use adapters to fit the components you want to use.

I haven't done the detailed comparison but I did find a few cases where the 4AN length of steel braided hose (12in) was more expensive for the same hose (same maker, style and length) in 6AN diameter. So there may be an extra expense by choosing 4AN. This makes sense if 6AN is more common.

Just saying to the OP, do your research. ;)

Sun Jan 14, 2024 7:18 pm

ashman40 wrote: ... So there may be an extra expense by choosing 4AN. This makes sense if 6AN is more common.

Just saying to the OP, do your research. ;)

Hey sorry, I missed your earlier post above about 6AN vs 4AN - You're right, and to your point, I agree. Although 4AN is widely available, it's not as common as 6/8 sizes, so either the fittings are more expensive, or aren't available in certain combinations. 5AN is the same, a weird off size that's hard to find. As far as flow restrictions go, it's possible, but it seems like you'd really have to be pulling hard for a long time with a bigger-than-stock engine to see it.

Sun Jan 14, 2024 7:19 pm

Great follow ups, thanks.

scrivyscriv - I thought about running bulkhead fittings and new tube inside the tunnel but just couldn't talk myself into re-running the hard line, so I think I'll flare both ends for tube and nut using -4an.

ashman40 - Regarding the availability of 4an vs 6an filters, etc... good to keep in mind but I also see lots of filters, regulators and pumps with 1/8 NPT female threads where I could use a 1/8 NPT to 4an fitting.

I'm still thinking through questions like 4an vs 6an for the flexible lines and whether or not to run hard or flexible line in the engine bay itself but, regardless, I hear you on wanting quality lines. Although I have quality line and have built AN hoses in the past, I used raceflux pre-made lines on my old CTS-V racecar for peace of mind and may do the same again. We'll see.