3.2 Carrera engine swap: fuel system changes

[Shuie]

I’m in the beginning stages of swapping a 3.2 Carrera motor into what basically was a stock '72 911 T.

So what kinds of changes do I need to make to my fuel system?

The fuel pump is obvious since my previous motor had MFI. So what fuel pump do I need and where should I mount it. Do I find a used 3.2 factory pump? If so, which one? My parts catalog lists two: 911 608 102 02 and 944 608 102 04. Or better yet, is there a readily available non Bosch pump that is sufficient? I know later cars had fuel pumps mounted in the front of the car. Is relocating the fuel pump to the front of a '72 an easy enough task, or should I just mount it in the rear by the torsion tube where my MFI fuel pump was? If I move it to the front, do I need to change suspension cross member? Anyone have any pics of a relocated fuel pump?

I’ve also read some old posts that mentioned changing the fuel tank when doing a 3.2 swap to prevent surging when the level is low. Sounds like a good excuse to buy a 27 gallon fuel safe and knock a hole in my hood for center filler

What about the lines through the tunnel? Should I yank the old MFI lines and install new Carrera lines? Or are the MFI lines sufficient since they will be seeing less pressure?

Moving on to the rear of the car. My parts catalog shows only a filter assembly and a hard supply and return line. Is that it, or do I need a fuel accumulator also like on a CIS car? Is there anything special I have to do to the fuel system on this end of the car?

TIA

[addictionMS]

A few thoughts,

I believe you need to use the factory pump, certainly the easiest choice. The EFI depends on a particular fuel press and flow rate. the regulator on the back of the motor is what helps stablize that.

I had to turn the regulator on the passanger side 90 degrees so it woudl not hit my shock tower on my 1970, I tipped it up.

If you have an aluminum cross member in the front of the car putting the fuel pump there is easy as pie, there are stock holes in the crossmember for the pump to mount to.

Running the fuel lines is a bit more of an issue, I choose to run two stainless steel braided AN-6 lines rather than use the existing ones. I weleds an AN-6 fitting on to the bango fitting on the fuel pump. I ran the two line in the tunnel, ensuring that don't rub on the shifter, throttle, and clutch.

I did run my race 3.2 with the pump in the back, so that should work, but I have been told the pumps were designed to push not suck, I had a AN-8 line feeding the pump.

I used an AN-6 inline filter, about $100 with replacable filters.

I would suggest that you also consider replacing the fuel lines that go over the top of the motor, they are well known to swell and leak over time, you can not see the leak unless the motor is running and there is fuel pressure

And yes the only way for this to work is with the 27gal fuelsafe cell and center fill (just incase you are building justification for the family CFO)

Jim

[Shuie]

Thanks Jim! I wasnt sure about a lot of what you said, but I knew I needed the fuel safe cell and a center filler

[Shuie]

bumping with a pic request for an installed 3.2 carrera fuel filter assembly and a forward mounted fuel pump. If its not stock, show me how you did it.

Also, if I kept the fuel pump in the rear, wouldnt it get in the way of the DME wiring harness going through the rear bulkhead?

TIA

[jbrinkley]

don't know if this helps. I'm sure others have some better pics

[DonDavis]

Sherm,
What did you do with your lines and pump location?

I have all lines out from the tunnel back. What's recommeded?

[Shuie]

I really havent gotten into my fuel lines yet but Im going to mount the pump in the front of the car somewhere.

[Rot 911]

Sherman, if you are planning on using the Carrera metal lines that run from the end of the tunnel up to the fuel filter, I have one that I never got around to installing on my '86. Make you a good deal on it.

[Shuie]

I'll take take it. let me know where to send the money.

Thanks!

[Rot 911]

Originally posted by Shuie
I'll take take it. let me know where to send the money.

Thanks!

I'll figure out which one it is, take a pic for you and quote you a price.

[IROC]

I used a Motronic pump and mounted it in the rear where my CIS pump resided. No problems. I used all the existing CIS fuel lines (supply and return to the tank). Unfortunately, I don't know if the MFI used the same set up (fuel line wise). I used "Motronic" fuel hose from my local Volkswagen parts place to run from the fuel pump in the rear to the fuel filter (all I needed was a banjo fitting to interface to the pump outlet). I also cut off the threaded fitting at the outlet of the fuel pressure regulator and installed a barb fitting and ran fuel hose from there back to the return fitting at the tunnel.

I made a simple braket to mount the fuel filter and attached it using the old mounting holes for the CDI unit.

Mike

[randywebb]

"forward mounted fuel pump."

If you have Al cross-bar, it just mounts to the provided holes or whatever -- IIRC, there is a diagram on the parts CD of how it mounts.

I'd also like to see a true pic tho...

[1972_911T]

Sherman if you try putting the pump in the rear on the original MFI mounting as you asked above your are right in presuming the wiring will be in the way I found this out when I fitted my wiring a couple of weeks ago. I ended up cutting the mout of with the grinder.

For the rest of you who have done this conversion is a new fuel tank really a must or will it work with my 72 tank?

The other Q I have is if I keep the original fuel lines running through the tunnel and then want to use original mortonic line at the back upto and from the engine how do they attach to the soild lines? on my MFI car the supply line is thicker bore than the return is this the same on the 3.2's?

Steve

[Shuie]

Well, this is almost done. I'll update later with any part numbers, etc. right now most of this is off the top of my head or copied from other posts. I'll try to finish this and post a conclusion with the relay wiring for the fuel pump ASAP.

In the front, start by replacing the lines between the front bulkhead and the tank/pump with the tank removed. Nothing earth shattering here, search to find out how to remove the tank. You are going to be working in really tight quarters with the brake lines and steering rack still attached, so be patient when you are trying the press the fuel hose over the nipple at the bulkhead. Soap, lithium grease, or silicon spray will help you slide them into place easier.

My car had a clean original non baffled '72 tank. I've read here where this tank can cause grief with a 3.2, so I replaced it with a Carrera tank.

There is a fitting that screws into tank from the return line that is normally attached to the bulkhead of a Carrera and cannot be bought separately. Buy the fitting from a salvage yard and attach a piece of fuel hose to it. Use a similar strategy for the banjo fitting at the end of the supply line that connects to the check valve on the fuel pump. You will need two crush washers and a captive nut to attach this line. Its less than $10 worth of new parts and another $10 for the banjo fitting and return line fitting from somewhere like partsheaven.



Between the tank and the pump there is a 4" piece of fuel hose that is bigger than anything you will find in a auto parts store. This is a $45 factory part. No way Im paying $45 for less than a foot of fuel hose. Check with a local speed shop, they will have fuel injection line thats big enough to use, size will be AN-8 or 1/2".

I mounted the fuel pump to the existing steel front crossmember with 4" worm clamps over a rubber sleeve. The rubber sleeve was from the hardware store and is actually supposed to be used for coupling sewer pipe. Not real elegant, but I think it will work. I used SS worm clamps for a touch of class I decided against using an aluminum cross member because I didnt want to drop my front suspension.



From the rear bulkhead, I extended more of the high pressure fuel injection hose up through the old brackets and attached it to a set of factory supply and return hardlines that I cut short.





Recap:

-The american fuel injection hose is close enough to work. You can get this at your local autoparts store. Or you can buy the real stuff from Pelican if you want it. I bought the fuel hose from the local Autozone. Make sure you buy 'High Pressure Fuel INJECTION Hose', don't let them give you breather/evaporative system hose. Got to a speed shop for a section of AN-8 or 1/2" hose for the section that connects the tank to the pump.

-Use a tubing cutter for the hardlines. You can get this from autozone also if you dont already own one.

-Get the banjo fitting for the fuel pump and the tank fitting for the return line from a salvage yard.

-Get the fuel pump with the check valve from Pelican. Its $20 cheaper here than anywhere else and you get free shipping on this item. Don't forget the captive nut and the crush washers.

Things you might do while you're in there.
-Clean and POR treat the edges of the tank while its out.
-Clean and POR treat your front pan while the tank is out
-relocate battery
-rear brake line refresh

Parts:
(1) rear supply line - 911-356-083-01-OEM ~$50
(1) rear return line - 911-356-085-05-OEM ~$80
(1) clip for above lines - 999-511-093-02-OEM ~$5
(1) fuel filter - 928-110-253-06-M67 ~ $20
(1) fuel pump w/check valve - 944-608-102-04-M14 ~$200
(1) - captive nut for fuel pump check valve - 928-110-475-01-OEM ~$5
(2) - crush washers for above - 911-608-902-00-OEM ~$0.75
banjo fitting for supply line from pump ~$5 from salvage yard
return line fitting for tank ~$5 from salvage yard
3.2 fuel tank ~$350 from salvage yard
6ft - high pressure fuel injection hose - 3/16" ~$20 from local autozone
6ft - high pressure fuel injection hose - 3/8" ~$30 from local autozone
worm clamps ~$5 from local autozone

Tools:
small Tubing cutter ~$10

Total Damages
$750 in parts above, + rear brake line refresh, + POR treatment, + shipping for everything. Probably close to $1k when its all said and done.

You could probably do it cheaper, or maybe a little better, but that's how Im doing it. Im not a mechanic by trade, so if I'm doing something thats going to cause the car to burn, please respond here.

I hope this helps someone who might head down the same road of doing this swap on their own in the future.

[DW SD]

Sherman,
The photos you show (#2 & #3) are using worm drive clamps. The holes in the clamping surface have a tendency to cut into the rubber and those clamps are meant for low-pressure applications (2psi to 10psi) like carbureted fuel systems. I'd suggest you use swaged or AN fittings for high pressure fuel lines. (swaged is like the factory does). They use a hydraulic crimping tool to permanently clamp the rubber line over the metal hardline.

If you choose to use hose-clamps, at least use high quality ones with no holes in the clamping surface. The Porsche factory uses Norma Clamps (at least some are Norma brand) which have a solid steel clamping surface. AND I'd suggest double clamping the lines at the very least. The return line from the regulator is not high pressure, only the pressure line from the pump.

Finally, I'd recommend you thoroughly pressure test the system in some way before installing the engine. As it stands now, I have a feeling you will have leaks.

Straight, cut-off hardlines are not really suitable for slip-fit hose connections.

Hope I'm not the bearer of bad news. Fuel is not something with which to take chances.

[DW SD]

Here's some more information which should help you. I had similar issues when I revamped my fuel system. PO had cobbled something together which not only leaked, but virtually every piece was completely unsafe.

Take a look at this thread: this is how I attached AN fittings to the 8mm factory stainless hard, fuel lines. Earl's (AN fittings company owned by Holley) tech support said these are good to 60 psi or something thereabouts.

AN fuel fittings for fuel system 8mm ~ 5/16th"

If you converted the inlet side of the fuel filter to -6 AN (I bought an adaptor from Earl's that worked) then you could run AN between the hard tunnel lines on the pressure side to the filter and then the stock Porsche lines to the fuel rails.

Again, the outlet of the regulator is low pressure. I would still change to safer clamps, but that should solve those problems. There still is likely an issue between the pump and the hard line into the tunnel. A similar solution would work. I think Earl's may have the right banjo fitting.

Again, I hope this helps.

Doug

[Shuie]

Thanks Doug. Thats why I posted the pics here. I can flare the ends on the metal lines pretty easily. Where do I get the better hose clamps from?

What about the location under the drivers side rear bucket for the lines? Should I have used the lower set of hose guides? I didnt think about it until after I had tightened everything up, but the current location of the lines is where my charcoal cannister lines were before. Is this too close to the tranny for fuel lines?

TIA

[DW SD]

I've bought nice, non-shredding German hose clamps from both the Porsche and Mercedes dealer. I bet Pelican sells them. They are more expensive, but only $1 - $2 ea.
OR
For a few examples with pictures, go to www.mcmaster.com page 229. Scroll down to the third and fourth clamps pictured (non - perforated worm drive hose and tube clamps). Top of page 230 shows a lined clamp, which won't eat up the rubber, either.

Next, I'll take some shots of my current fuel system setup. That includes at the front pump and at the tunnel. My engine is currently out.

With the AN connections showed in the provided Pelican link, you don't need to flare anything, it is simply a crush tube fitting. I started exploring flaring myself, but couldn't find the right hardware to use for the male and female connections to make the flare work properly. If you know where to get that, then go for it!

Doug

[78-911SC]

Doug and Sherman looking forward to your pictures. I'm only a matter of weeks from that portion of the project.

[DonDavis]

Sherm, I bought some of the good clamps at BAP. They had a decent selection.

Doug,
Your fuel lines sound great. Please put up some pics and additional info please!

Thanks!!