Bulvot

Having recently made my own fuel hoses, I'm sharing what I've learned.


If all you want is a parts list, skip to the end and/or download the attachment.


None of what I'm sharing is proprietary, secret or otherwise something that isn't common knowledge. None of this was discovered by, or in any way unique to, any 928 vendor. This is all generic information. If you poke around on other Porsche forums, or even European car forums in general, you'll find that the information on the metric fittings is common knowledge. They are standard specifications. As are the parts sources for those fittings. And if you look around on any car forum at all, you'll find that AN hose and fittings is very common knowledge. Not to mention the aerospace and manufacturing industries.

With that said...

The fuel fittings in the engine bay of the 928 are DIN 7631, sometimes called a Metric 60 Degree Cone. Which is a 60 degree bubble fitting. Most of them are "standard", which means that the male sides are concave and the female sides are convex:




The following connection points in the 928 engine bay use that standard:

-Main feed line connection to the front damper (hose is female, damper is male)
-Front passenger fuel rail connection to the hose going to the front damper (hose is female, rail is male)
-Front damper connection to the hose going to the front passenger fuel rail (hose is female, damper is male)
-Front driver fuel rail connection to the front damper (rail is female, damper is male)
-Rear passenger fuel rail connection to pressure regulator (fuel rail is female, regulator is male)
-Pressure regulator connection to the hose going to the rear damper (hose is female, regulator is male)
-Rear damper connection to the hose going to the pressure regulator (hose is female, damper is male)
-Rear driver fuel rail connection to the rear damper (rail is female, damper is male)
-Fuel adapter between regulator and fuel cooler where it connects to the hose to the cooler (hose is female, adapter is male)

I don't know about the 1987.5 and newer threaded fuel return connection on the "bottom" of the pressure regulator that goes to the fuel cooler. Mine is an early 1987 with a barbed connection. I presume that on the newer ones it's also a DIN 7631 connection, with male on the regulator. But, you'll need to check this to be sure.

Now, things get a little "funky". There are two "inverted" connections in the 928 engine bay. These two connections have the male side with convex seals and the female side with concave seals. The reverse of the diagram above. The following two connections have this inverted configuration:

-Main feed line on the passenger fender where it connects to the line to the front damper (hard line is male, hose is female)
-Fuel cooler where it connects to the hose going to the pressure regulator (fuel cooler is female, hose is male)

The last information needed is that on the early 1987's (and presumably earlier cars), the barbed fuel connection on the regulator is 8mm (5/16").

All under hood fuel fittings on the 928 are steel.

With this information in mind, we can start to make decisions about hoses and hose ends.

First, this is all predicated on the requirement that everything is brand new. No used or rebuilt hose ends. If you want rebuilt, just take your old hoses to your local hydraulic fittings store (e.g. Colliflower) or send them to 928sRus.com.

For the hose ends, you need to decide if you want to use aluminum or steel to match the OEM fittings. In general, aluminum is for "low" pressure, and steel is for "high" pressure. It's also not generally recommended that you mix aluminum and steel compression fittings. They will usually work, but can be susceptible to galvanic corrosion and galling. For those three reasons (pressure rating, corrosion, galling), I chose to go with all steel for my fuel lines. Aluminum would absolutely work, but I feel that steel is "right".

There is one significant advantage to going with aluminum hose ends. You can get crimp on hose ends that have the correct DIN 7631 flares for all but the two "inverted" connections. That eases installation and makes things tidier. You'll have to order these hose assemblies to be made for you, though. Unless you want to invest $2k to $5k in a basic crimping tool.

A disadvantage with going with steel hose ends is that they only come in AN style flares. So, you will need to use an adapter to connect the hose end to the 928 fuel components. The good news is that there are steel adapters available for all but one inverted connection.


The other major decision that you have to make is what kind of hose to use. Rubber or PTFE. For my project, I used PTFE for everything except the fuel return line that must be compatible with the barb on the regulator. PTFE hose cannot be used for barbed connections. Rubber usually has a tighter bend radius and is cheaper. You cannot mix PTFE and rubber hose ends and hose. PTFE hose ends must be used with PTFE hose, and likewise for rubber hose ends and hose.


The easy path for all of this is: Go with aluminum hose ends with crimped on metric fittings, your best source will be https://batinc.net. Page 12 of their PTFE hose end catalog (https://irp.cdn-website.com/e112be6e...d/tfefit22.pdf) has their aluminum metric crimp hose ends. Just figure out the hose lengths that you want, then call them and order the hoses to be made for you. Couldn't be easier. Just keep in mind that -6AN PTFE steel braided hose will have a 4" bend radius. So for the regulator to rear damper hose, you need to leave lots of room for a smooth loop, or use two extra 90's and a union to make the "U". Mock it up with regular hose or string, measure, then order. You will still need the special inverted adapter to connect to the main feed line, which BAT carries.

When you select your hose, keep in mind that there is PTFE hose that has a black nylon coating. It looks very good and practically OEM. I highly recommend it.

For me, since I went with steel for everything possible, this is what I did:

Main feed line:
-Inverted (concave) Female DIN to male 6AN adapter (aluminum, the only material available for this adapter)
-2x 90 degree 6AN steel hose ends
-PTFE steel braided hose with black nylon coating
-Standard Female DIN to male 6AN steel adapter

Passenger fuel rail to front damper:
-2x 90 degree 6AN steel hose ends
-PTFE steel braided hose with black nylon coating
-2x Standard Female DIN to male 6AN steel adapters

Fuel pressure regulator to rear damper:
-4x 90 degree 6AN steel hose ends (I used two of the 90's and the 6AN union to create the "U" without having to bend the hose)
-PTFE steel braided hose with black nylon coating
-2x Standard Female DIN to male 6AN steel adapters
-Male to male 6AN steel union

Fuel pressure regulator return line to fuel cooler:
-Standard male DIN to male 6AN steel adapter
-M16 self centering bonded washer (to seal the above adapter to the fuel cooler)
-5/16" (8mm) Gates barricade fuel injection hose
-2x fuel hose clamps

On all of the hoses, even the return line, I put fire sleeves. On the PTFE hoses, I secured the ends of the sleeves with heat shrink.

Two important points:

1) The inverted flare adapter for the main feed line on the passenger fender appears to have only one source. And I did a lot of scouring and calling around. Https://BATInc.net appears to be the only one who makes that specific adapter. And they only make it in aluminum. So, if you want to use anything other than a remanufactured OEM line, you must buy their adapter. Might be worth getting a couple of them to have a spare.

2) A proper adapter for the connection to the fuel cooler just doesn't seem to exist. Maybe a company in Germany is making one, but I had no luck with finding one. Using a self-centering bonded washer between the normal steel flare fitting steel adapter and the fuel cooler fitting is absolutely acceptable. Just clean up the surface of the fuel cooler fitting first. Standard practice, and it's "low" pressure at this junction anyway. If you find a male DIN 7631 inverted (convex) M16x1.5 adapter, please post the specifications, link to manufacturer, and link to distributor.


I recommend that if you're building your own hoses, as I did, that you get the following:

-Critical: PTFE AN hose assembly tool (for example: Aeroquip FBM3646). This tool is absolutely critical to properly seat the PTFE hose in the olive barbs during hose end assembly.
-Critical: AN hose pressure test kit. This lets you plug one end of the hose and put a valve on the other. You then fill it with compressed air and dunk it in water to look for bubbles. This is critical to make sure that your hose assembly has no leaks.
-Aluminum vice inserts to hold the hose and hose ends during assembly. This made assembly infinitely easier.
-Hose assembly lube (for example, Earl 184004ERL). This makes assembly of the hose end so much easier.


Attached is a spreadsheet with the parts and links to sources for everything that I needed to build my hoses.

Here is an example of one of the hoses that I made, with the fire sleeve installed:



And a close up of the hose with some of the black nylon cut off. You can see how the black covered hose looks fairly close to what you would expect from an OEM hose.

hwyengr

This is all cool info, but there's no way in hell I'm building my own mission-critical parts. Whatever GB charges for fuel hoses is cheap insurance to keep my car from burning down.

Zirconocene

There was a lot to digest but I think you captured everything that I also learned when making my own fuel hoses. From my own notes, not anywhere near as well organized as yours, I have the following:

"DIN 7631 60° or DIN 3902 / Millimetrique 24° concave seat on the male fitting (the Globeseal seat is not designed to work with Japanese JIS 30° seat). It cannot be used with a crush washer.

Indications that DIN2353 is interchangeable with DIN3902"

Cheers

Speedtoys

If I had a hydraulic test kit at home..I might think about this..but...without that, you're right..but I dont think I would spend a few thousand on a reputable test bench for the 8 hoses I will ever make.

Bulvot

Like I said in my first post, if you're not comfortable assembling your own lines, then just call BAT and have them made. Some of the benefits of having them do it: they are very responsive and ship fast, they have crimp versions of the aluminum metric connectors, or you can choose steel, and PTFE or rubber lines.

Precision Motorwerks uses all aluminum hose ends, versus the steel used by the factory. All of Precision Motorwerk's fuel lines have standard reusable aluminum hose ends. They are the common screw together hose ends that you can get anywhere and do yourself, just like what I used (except mine are steel). The only exception is it looks like on the rear regulator to damper line they used aluminum crimp on hose ends.

Here is an example of their hose directly from their site:



The main point is...it's all aluminum fittings. If you're concerned about "mission critical", then you should stick with steel like Porsche did. Steel is significantly stronger and more durable in this application.

On Precision Motorwerk's hoses, It doesn't look like anything other than the main feed line are PTFE lines. Just standard light weight rubber "racing" hose. See here for an example of identical looking hose: https://irp-cdn.multiscreensite.com/...ded/lwhose.pdf (or just do an internet search for nylon braided AN hose). The significant advantage of that type of hose is the very small bend radius, which is perfect for the regulator to damper "U" hose.

And their rubber hoses are 100% fine. As good or better than stock. No question. Nothing wrong with it at all. Which means that they will need the same level of inspection and regular replacement as stock fuel hoses.

However, you can get PTFE hose with all kinds of sheathing, and convoluted to boot, so maybe it's got actual steel braiding under the nylon weave? I would want some assurances before ordering. Because the tight bend radius needed to keep the stock hose length for the rear "U" line wouldn't be possible with normal PTFE hose (non-convoluted).

Anyway, you're just paying for someone's time to cut the hose, slip it into a fitting, and run a nut onto the fitting. Same exact thing you can do at home. Or, pay less for a dedicated automotive plumbing shop to do.

Or, get proper crimped on fittings with metric hose ends for all of the hoses and PTFE to boot. And add fire sleeves to all of them. You don't have to do it yourself if you don't want to. BAT and many other shops will be happy to do it for you at a very reasonable price.

Or, buy from Precision Motorwerks.

It's good to have choices. Do what is best for you. That's what I did.

Bulvot

Your prior research and work on this was very helpful to me. And then I jumped into the rabbit hole of AN vs JIC specifications, the various DIN specifications, etc.

Are you suggesting that the male DIN 3902 24 degree seals are the same as DIN 7631 60 degree seals? And that DIN 2353 24 degree seals are compatible with both? I can see DIN 2352 being compatible with DIN 3902 just based on the cone angle (and no additional research), but I don't see how they could match up properly with DIN 7631?

Please enlighten me on that point

Bulvot

Hydraulic pressure test kits are relatively inexpensive. But, the standard for pressure testing AN hoses is to use AN pressure test kits. Also inexpensive.

Worst case, just take your assembly to your local Colliflower and tell them to what pressure you want your hose tested. Just don't go above 250 psi for the regular hoses and aluminum fittings. PTFE with steel braiding and steel fittings should be good for 1,500 to 3,000, depending on the components that you selected.

GregBBRD

Your agenda never ceases to amaze me!
I'll correct all of your misinformation, in your text, in blue.
Try harder to know what you are taking about, before mentioning me or my products....ever.

And....the major different between using an adapter with an AN fitting on the hose is that you've introduced an additional junction (an additional potential leak)...on every hose end.


Again: Leave me and my products out of your posts. (You have officially been warned, in a friendly manner.....in the past and now, today. The next time will not be friendly!)
And keep up the good work! (Also sarcasm.)



Update: Regarding your added picture....we haven't supplied that hose for over 10 years, like the text above states.
The picture, like on many websites, is simply a representation of what we sell.

Zirconocene

@Bulvot : I can't verify the compatibility, to be perfectly honest. I got so far down in trying to understand what I was looking for that, ultimately, I lost track of the sources for some of the information I found. For what it's worth, that particular note I have has a link to Pegasus Racing, so maybe there's something there.

Until I started working with the AN/JIC fittings I didn't quite understand why a 24 degree fitting would be compatible with a 60 degree, but not a 30 degree, but it's all about the radius, as far as I can tell. JIC fittings are a hard, angular 37 degree shape, as opposed to a gradual radius. I don't really have the skills to go through and calculate contact area differences between the 60 degree and the 24 but I sort of presume that the properly matched pair would be higher. As these fittings rely on this metal to metal contact for sealing, compatibility alone might not be enough to reach the quoted operating limits. That said, there's a lot of overhead between 55 and 3k psi, so...

Cheers

Bulvot

@Zirconocene , thanks. That's really interesting and I'll have to think on it.

Moot point now. All back together and working properly. No leaks.

GregBBRD

If you read my post # 8 (above), I discuss the issues we have with AN steel to steel pieces leaking. Almost 100% of the AN steel hose fittings and adapters are made in China. Getting a good seal on the thin contact area of a 37 degree pair of Chinese steel parts can require some very careful attention.
On the flip side, my aluminum direct fit metric hose ends (crimp style for PTFE hose) are made, to very precise standards, in Germany.

Speedtoys

"Same exact thing you can do at home"

We had a racer, well, a couple of them, that built their own oil lines at home.

After about 5 weekends, of numerous oil line failures (because they just threw them together)..they had to post bond to enter events, because it takes about 20-30 min EACH time you oil down the track, to deal with it correctly. And the impact to the schedule and other people's races was becoming unreasonable...so..they had to start covering the cost of lost time. Sun rises and sets on a =set= schedule.

Not saying everyone is not up to the challenge....

But you're really generalizing how trivial DIY pressure lines _can_ be...especially in such a mission critical use case.

I dont care I guess who you buy a line assembled from, but..then you start considering what skin they have in the 928 world to do it right..or not.

Even MOST transmission lines I would do at the local Hydro-Hoseman shop, except ONE in the engine bay...certain things require -that- pucker factor.


I hope yours do well, and I have no reason to believe you did anything wrong...but, who is whispering in your ear all the BS about some other vendors materials?

Speedtoys

Stuff like this is like me wandering around home depot for garden hose ends...

Why couldnt the hose people just sit and have a meeting one day a century ago...

Bulvot

Thanks. I prefer not to discuss vendor products, but someone else brought them up. The vendor has clear photos of their hoses on their web site. And those photos very clearly depict aluminum non crimped hose ends on non ptfe hoses. The photos are facts that anyone can view. No harm in accurately describing what's in a public photo being offered for sale by a vendor.

Speedtoys

"but someone else brought them up."

Now you're getting the start of a hint how heresay works.

Lots of pointed effort and emotion into diagnosing a product from a photo