Wednesday, February 8, 2017

Fuel System Install Part 2 – Hard Lines, Front Soft Lines & Pump Plumbing

When we left off last, the rear soft lines had been completed and the fuel pump module had been placed in the tank.  Moving forward from here, we started phase 2 of the fuel system install by permanently mounting the fuel tank in place using butyl strip caulking to seal the tank flange to the trunk aperture.  With momentum on our side, the selection and routing of the short lengths of soft line to the trunk area bulkhead fittings could be easily worked out.  Once we had something that allowed clean bends in the hoses and no interference with any surrounding points, the lines and fittings were mated up and set into place.  Almost a shame that all of this will be covered by the trunk floor during upholstering.

Next on the agenda was perhaps the most difficult aspect of fuel system installation:  Custom fabricated hard lines that make up the bulk of the feed and return line length.  I am a bit particular in how fluid lines look, and prefer that they remain as unseen as absolutely possible without compromising function.  In addition, I demand that all fluid lines are leak-free straight off and that they are easy to work with.  LOTS of builders (most in fact) use stainless steel tubing for hard lines in both brake and fuel systems and there is absolutely nothing wrong with that.  However, anyone who has worked with stainless will tell you it can be rather unforgiving to bend and flare and leaks are something to be chased on all too frequent of occasions.  Coupled with that, stainless is rather expensive and can be somewhat variable in quality.

Over the years, I have become an absolute cheerleader for American-made copper-nickel-ferrous alloy (a.k.a. “cunifer”) hard line material in everything from brakes to fuel and oil lines.  This material is very durable, will not corrode, bends easily and cleanly, flares like a dream and is good to about 3000psi. 

Since most of the fitting hardware on this fuel system is of the 37-degree AN flare variety, the hard lines will have to be flared accordingly.  And since I insist on using an aircraft industry roll-flaring tool for hard line work, the cunifer material outshines any stainless tubing in almost all respects, save perhaps, visual appeal in an exposed application.  What can I say, some people like shiny stuff!

The feed and return lines for the Boss are fabricated from 3/8” cunifer material as an (almost) matching pair of lines run down the inboard side of the subframe connectors from the rear to the front and then passing through the right front subframe to just under the right torque box enclosure. Of course, this sounds so easy like that, but there is about 6 hours of work in fabricating these two lines to ensure they match beautifully and terminate in exactly the location they are needed to allow the front soft lines to be fitted with precision.

In response to the many questions I get regarding tubing work; it’s worth mentioning that you should consider the investment in top quality tools a necessity in making hard lines worthy of display.  Quality tubing benders are an absolute must and the same goes for flaring tools.  I swear by my Imperial Eastman benders, Ridgid #376 roll-form 37-degree AN flaring tool, Kwix-UK tube straightening tools, and the Eastwood #25304 pro flaring tool and can’t imagine being able to do the work on this fuel system without them!

With hard lines run, the fuel lines could be finished up with the final (and rather tricky) job of making the front soft lines that pass through the right torque box to the inner apron in the engine bay.  It begins with careful placement of the pass-thru holes that will get grommets inserted to prevent any damage to the rubber lines as they pass through the sheet metal panels.  Since the lower and upper hard line “pierce points” are almost lined up from front to back, the rubber lines can be passed through the torque box is a “lazy S” fashion that keeps the lines kink-free and away from any sharp edges along the way.

With a bit of extra hose length on both ends of each hose, the apron fittings are secured first to establish the absolute routing of the lines in the fender well area.  Following that, the rear hose ends can be precisely cut to length and the AN fittings added to mate to the hard lines perfectly and with minimal visibility.

With the exception of a few small detail bits, that puts a period on the fuel system installation!  The routing of the lines is such that, even when on the lift, the system is exceptionally tidy and gives little away to the fact that the car will be fuel injected and therefore maintains the style of subtle detail we’ve been after from the start.
Before the rubber lines could be run efficiently, a little noodling on fitting choice and position was required.

With fittings chosen, it was a simple matter of measuring and cutting each hose to length and assembling the fittings and clamps.  Done!

With the hard lines flared and tube nuts installed, the rear hard line connections were made.  These fittings almost fell together on their own.  A reward of very careful line layout and fabrication.

The cunifer hard lines were carefully formed to the inner subframe connector contours and remain out of sight with the car at ride height.

Using factory holes through the front subframe, the hard lines were routed cleanly through to the outside of the rail and aligned with the lower rear torque box.

Here you can see the finished hard lines at the front termination .  The soft lines will mate directly to these lines once they have been passed through the torque box rear wall.

I am frequently asked about the type of line clamps I use in my builds and here they are "nekid".  These are Quick Clips and install in a drilled hole using a "Christmas tree" barb stem.  Very clean.

Another shot of the Quick Clips used for mounting the hard lines.

Here, you can clearly see the routing of the front soft lines into the forward wall of the right torque box.  Note the pass through holes have grommets installed to eliminate damage to the soft lines as they transition through the torque box.

Here, the front hard line to soft line fittings are visible.  You can see how inconspicuous the entire operation is, giving little away that the car will be fuel injected.


  1. Impressive. Looks like it was always meant to be that way from the factory! Hadn't considered using cunifer tubing for lines. Great choice. So at the rate you're going, you should have the Boss on the road in a few weekends, right? :-D

    1. Thanks Dennis! Cunifer has really become my "go to" hard line material of choice!

      And boy do I wish that time line was true! LONG way to go yet, but it feels good to make progress in bigger chunks lately!

  2. Professional as always Sven!!!! Good recommendation for flaring tools. I was in Oxford just before Christmas - helping out with a driverless car conversion. Had to hijack the onboard ABS system to control braking. Required lots of flaring but these guys found the slickest tool for doing it. I meant to get the part number but forgot in the mad rush at the end. I'll have to ask the guys over there where they got it. Looks like 2017 will be fruitful for you!!!

    1. Thanks RJ! I'd be really interested if you happen across the tool description those fellas used. I am always open for better tools if they're out there!

  3. Sven, Nice work. I am getting ready to run the nickel/copper fuel lines on my 69 Mustang for my fuel injection system & was wondering where you purchased the tube nuts for the for the fuel lines?.

    1. Thanks Mike!

      I use conventional steel Aeroquip AN tube nuts and sleeves as follows:

      -6 Aeroquip AN Tube Nuts P/N FBM3572
      -6 Aeroquip AN Tube Sleeves P/N FBM3680

      The Copper/Nickel "a.k.a. cunifer" tubing I use is:

      S.U.R.&R. E-Z Bend Tubing P/N BR-EZ400. This is 0.375" O.D. with a 0.028" wall and will work well with high and low pressure fuel systems.

      Hope this helps!

    2. Thanks Sven that helps a lot. What are the connectors that the tube nuts screwed to that are fitted into the fuel line hose?. Do you have the part numbers for those too?.

    3. The black female AN anodized fittings are standard Aeroquip Socketless Hose Ends. The male hose ends are Aeroquip Socketless -6 AN Hose Barb to Male -6 AN.

  4. I get zero hits on Google for any combination of: nekid quick clips with Christmas tree barb stem

    1. Here's the link to the distributor for the Quick Clips I use:

      Hope that helps!