Question - Fuel Line Size

[Tidybuoy]

Got a question regarding fuel line size. This is for my '74 CIS and I want to replace the high pressure fuel hose that is just before the hard plastic lines to the fuel distributor.

I previously purchased high pressure fuel hose that was 7x3 >NBR<>CR< but this line, after only 6 months started leaking. It was high-quality German line.

So, when I look at PET, I only get a part number and no sizing. When I go to the Pelican site, there are only 3 sizes available; 6x10, 7x13, and 8x13.

Then, when I look at my existing hose, there is no way the inner diameter is 3mm. So what size should I be using and how does the sizing system work?

Any advice would be appreciated.

[manbridge 74]

Scary. Was it leaking at a crimp? Can you measure the old line?

I imagine Len will clear things up shortly....

[Tidybuoy]

It was leaking right at the hose clamp. Fortunately, I had been working on the car for the last couple of months so when I started it up, the leaking was caught immediately and shut down.

[BoxsterGT]

Tidybuoy -

7x3 Hi Pressure Fuel Hose??? Now leaking at the hose clamp????? After only 6 mos ?????

The only fluid transfer component that I know of at the CIS with a 3mm ID is a Polyamid fuel LINE. There is Vacuum Hose in that size but its not made for fuel. If what you have carries fuel it should be Polyamid and semi-rigid and not soft and flexible as a hose would be. It cannot accept a crimp sleeve or a hose clamp, ever. If you or a PO have somehow substituted HOSE for LINE then this is a big mistake.

If you can be more specific in your description, perhaps with a few photos, someone here on this board can help I am certain.

Len at Autosportengineering dot com

[Tidybuoy]

Well, I ordered the 3 different fuel lines from Pelican (listed as 6x10, 7x13 & 8x13). When the hoses arrived, the 6x10 part is stamped on the outside 7x3 so go figure. That is the correct line but I have no idea what it's actual size is. It fit snuggly and I used double hose clamps where there was room - no leaking. I'm going to order new hose clamps as mine are only tight at the very tightest setting so they may be a hair too large.

[BoxsterGT]

Hi Vern-

CIS fuel systems run pressures as high as 70 psi, so hose clamps are not adequate, even when doubled up.

If you can post a few photos perhaps we can see what is needed and give you some advice.

Len

[Tidybuoy]

I don't have pictures with me here at work but these are the ordinary fuel lines (Before) the CIS system. That is, the fuel lines that pass thru the body to the fuel pump that is mounted at the rear on my '74. Basically, a metal line from the fuel pump passes thru the body and then a rubber fuel hose connects from this metal line to the beginning of the CIS system. The other fuel hose is the return line to the tank. These two short lines are at the very left back corner of the engine compartment (near the fuel filter and accumulator).

I do have all the correct hard plastic CIS fuel lines that connect to the fuel distributor, WUR, cold start valve, and the injectors.

[HawgRyder]

Interesting fact:
There once was a racer in NASCAR that "bent" the rules a bit.
He used a 3" diameter fuel line from the rear tank to the front pump to "slightly" increase the volume for his car.
I think, when they finally discovered it...they had to make a new rule to prevent it from being used.
Fuel lines are "in the mind of the beholder" so to speak...I usually go overboard with mine...using stainless steel...the best connectors...and lots of stabilizing clamps.
I like to prevent the fire...rather than putting out the fire.
Bob

[thumbdoctor]

Be careful when selecting fuel hose. The new concentrations of Ethanol under pressure will erode old style fuel line. Even the stuff with braided stainless on the outside. The racer's name was Henry "Smokey" Yunick of "The Best Dam Garage in Town".

[BoxsterGT]

Apparently the 7x3 is referring to the 7 as the nominal hose ID and the 3 is the wall thickness.

Most of the fuel fittings & hardlines on a Porsche are 8mmOD or 10mm OD, so a 7.5mmID or 9.5mmID hose is correct.

Best to measure what you need, as safety is the most important goal when dealing with fuel systems.

Len

[Tidybuoy]

Originally Posted by BoxsterGT

Hi Vern-

CIS fuel systems run pressures as high as 70 psi, so hose clamps are not adequate, even when doubled up.

If you can post a few photos perhaps we can see what is needed and give you some advice.

Len

The '74 uses hoses and hose clamps before the CIS system. I believe this was changed in '76 to lines with bango fittings.

The lines I am referring to are the ones circled in the photo:

[BoxsterGT]

Vern- Thank you. Your photo reminded me about what was used on the earlier models.

The early years of CIS came with many changes to the fuel delivery system. MY 73 still had steel tunnel tubes. In 74 Porsche went to White Nylon tube through the tunnel and hoses slipped over the tube with hose clamps. This method is fine with the low-pressure fuel systems of the earlier models, but for the high pressures of CIS it is not. MY 74 is the only year of this configuration.

In MY 75 Porsche went to Polyamid tube in the tunnel, with a Banjo fitting at the pump and Polyamid tube or crimped hoses elsewhere in the system. The Polyamid tube is very durable, is not subject to ageing, and is currently used today in most fuel injection systems worldwide.

If you still have the White Nylon tunnel tubes you might want to consider replacing them. As they age they turn brown & harden and become brittle, especially at the rear with the heat of the engine & exhaust. When disturbed they have a tendency to crack or split with catastrophic results.

Here's an example of the White (now brown) Nylon tube shown at right center of photo......



Just my 2 cents worth of advice.

Len

[BoxsterGT]

Thought I would bump this up as a reminder for any of you that still have original fuel lines in your 74 911.

The low pressure part of this CIS system allowed Porsche to get away with slip on hose w only clamps on this white (brown) nylon line. It is acceptable when you have the rear mounted pump, as the high pressure part is only at the engine. However, the hose from pump to accumulator (as indicated by Tidybuoy in post #11 above) and all other high pressure parts of the system requires improved hose or line and connections.

MY 1975 still has the rear pump but Porsche went to a Polyamid tube with a M10 Banjo at the pump and proper hard fittings upstream to the accumulator & filter. (I will post a photo when I can find it in my files.)

My point is, 74 911 owners MUST make an upgrade from their original white (brown) tunnel lines to anything more durable (Polyamid, SS or Aluminum tube), even when keeping the rear pump in place.

Of course the same can be said for the rubber hoses. Todays Methanol fuels require it.

Just my 02 cents.

Len

[BoxsterGT]

Another bump to members with 74 model year 911s......

Very important to get those "White Nylon" lines outta there.....

Len

[Tidybuoy]

Originally Posted by BoxsterGT

Another bump to members with 74 model year 911s......

Very important to get those "White Nylon" lines outta there.....

Len

Just FYI, Len (aka: BoxsterGT) made me new fuel lines for the tunnel and from the tunnel to the engine compartment. He also made me lines for the front when I moved my fuel pump to the front. All very good quality and reasonably priced too - Thanks Len!

[chrismorse]

When I got the car to its new home, I noticed a fuel leak. Putting the car up , we found this


The crispied section was right under the hot air dump at the heater valve.

After moving the pump to the front and installing a soft, bendable, stainless line inside the old supply line, we used an insulating sleeve, Stratoflex" to protect the lines in the area.



chris

[BoxsterGT]

Hey Chris-

I just noticed the photo above.....with a Brown Nylon fuel line to the Pump.

Do you still have this original line? If so, get it outa there fast. Thats the white (now brown) Nylon fuel line Porsche used for ONLY one year in the 911s, 1974.

ALL later years have the black Polyamide fuel lines that are practically bulletproof, and they are still used today by most auto Mfgrs worldwide.

If needed, I have Polyamide tube to correctly replace your original system, in case you have a concours type and want it original in every way.

Len

[bertsboat]

Do you still do the polyamide fuel lines?

Originally Posted by BoxsterGT

Hey Chris-

I just noticed the photo above.....with a Brown Nylon fuel line to the Pump.

Do you still have this original line? If so, get it outa there fast. Thats the white (now brown) Nylon fuel line Porsche used for ONLY one year in the 911s, 1974.

ALL later years have the black Polyamide fuel lines that are practically bulletproof, and they are still used today by most auto Mfgrs worldwide.

If needed, I have Polyamide tube to correctly replace your original system, in case you have a concours type and want it original in every way.

Len

[BoxsterGT]

Yes I do.

I make both the original 74 & 75 type for the Rear Pump in Polyamide (not white Nylon); and the later type in Polyamide for the front mounted Pump.

Please email me for info.

Len dot Cummings at verizon dot net

[BoxsterGT]

Bump to the top, as this is very important for fire safety.

These wonderful cars are getting more & more valuable.

Best insurance is to have fresh rubber where possible, especially on the 74 models.

Len