Making A Return Fuel Line Question

[piscator]

I made my own fuel injector lines, so I’m comfortable banging heated fittings into a plastic line, held in my jig.

However, I need to make up the fuel return line(s) in the photos below. These run from the fuel distributor to the fuel accumulator and the return line back to the tank. The original lines were plastic. My question is:

Aren’t these low pressure lines? Do I need to use the Cohline plastic tubing I used for the fuel injector lines? Or, could I use correct size rubber fuel line with Norma clamps over the fitting barbs?

I’ve got a lot of rubber fuel line from Belmetric in my shop, but I’m out of the plastic stuff. Ordering Cohline plastic tubing is not a big deal, but the flexible rubber might snake through the engine compartment more easily and I have it on hand.

Your suggestions, very much appreciated – always!

So many little details when you’re finalizing a major refresh project! But we’re getting close! Very close!





A couple of shots from the thread I posted:

[pmax]

Originally Posted by piscator

Ordering Cohline plastic tubing is not a big deal, but the flexible rubber might snake through the engine compartment more easily and I have it on hand.

Your suggestions, very much appreciated – always!

Nice work, Pisca.

The routing from the fuel acc/filter to the distributor is basically a straight shot, the 90 deg bend is already built in as your pic shows. I see no benefit of a more flexible tubing beyond the standard lines.

[BoxsterGT]

I make up these CIS lines on a regular basis, and always used the Polyamide tube.



That said, I see no reason why the Rubber Hose & Norma clamps will not work for the return.

Just my opinion of course, no experience to back this up.

I am happy to send you a short length of Poly tube, at N/C but for a little something for postage.

Len.Cummngs at verizon.net

[BoxsterGT]

Here is a return like yours w the rubber cover.......



Len

[piscator]

Pmax & Len,

Thanks very much for your comments!

P, I'm sure you're right. The flexibility isn't a particular advantage in the situation. In part, I was asking the question to test whether I understood the plumbing on the CIS.

Len, thanks for confirming that the low side doesn't necessarily need to be polymide. I appreciate your kind offer, but I already ordered polymide tubing from Matt at Belmetric. Those folks are very nice and they run a great outfit. I'm happy to send a little business their way. I may use the polymide or try the flexible, just to do something different.

There's a lot to learn on these cars and I'm still enjoying and working at it! I especially like that these cars are all mechanical. The solutions the Porsche engineers came up with are usually darn clever! (And sometimes aggravating)! ;-) It's fun to unravel it all. I have some experience with computers and electronics, but I just don't find those disciplines (on cars anyway) to be all that interesting.

Thanks again!

[BoxsterGT]

Let us know how it works out.

Always ready to learn about these wonderful cars.

Len

[boyt911sc]

Robert,

The return lines have low fuel pressure under normal condition. But when you get a flow restriction some where in the return line, it will build high pressure. You can not use fuel lines that are not rated for fuel injection application for safety precaution. A typical CIS single fuel pump could generate as much as 95~100 psi. I once used a non-rated FI fuel hose for my test stand and found out just in time the swelling of the fuel hose.

If you use it in your engine, it could be too late to notice the problem before it burst to cause a catastrophic engine fire. This is something you do not want to happen. You could build your own fuel lines but use the right ones.

Tony

[patkeefe]

There's a lot to learn on these cars and I'm still enjoying and working at it!
Also, learn to carry a fire extinguisher. An easily accessible extinguisher.
If you don't get the lines just right on the fittings, they will leak.

[BoxsterGT]

Tony, thank you for the advice and all your experience with CIS.

We have to keep these wonderful cars on the road for generations to come.

They are "Engineering Marvels" in their own right.

Len