Add fuel return for MFI in a SWB?

[MikeDL]

I'm considering putting a 2.4 MFI into my '68 T. I'm trying to think through all the issues that I'd need to solve (flywheel, finding an electrical console, throttle linkage) and I've found threads on most of them already. One issue I haven't seen discussed is the need to fish a fuel return line. Has anyone has done this? Do the new repro fuel tanks have the inlet for the return? Are the other fuel plumbing bits (FI pump, restrictor) readily available?

I'd appreciate encouragement / discouragement (or any other advice on this swap -- I'm not yet convinced I want to tackle MFI). Thanks!

[304065]

If your '68T is original, it should have a '68T motor in it.

The restrictor is NLA, if it even existed. The fuel restrictor is the "White Whale" of the MFI system: we believe it exists but nobody has ever seen it.

The real question is, will the engine FIT. I heard that you had to beat the tunnel and the top of the engine compartment to clear the MFI pump.

I must confess to having had thoughts of building a 906 "Spare" motor on a different case and saving my numbers matching case for Concours.

[MikeDL]

It's not very original, and I don't want it to be! The short explanation is that it used to be a track car (long version is on my website).

I had heard of the MFI pump clearance issue, but in a thread where someone mentioned needing to bend a flange down to get it to clear and that it wasn't a big deal. I'll keep digging on that issue -- Thanks!

If the restrictor is NLA, are people doing OK without having it?

[Grady Clay]

Mike,

I installed one in mine in about ’70. It is a 3/8” stainless pipe with Porsche 7 mm pipe barbs silver soldered in the ends. The connections are aft of the rear firewall and forward of the “smuggler’s box” – no connections inside the cockpit. It runs outside the tunnel along the passenger side. I pulled up the edge of the horse-hair sound pad. The pipe is entirely covered with two layers of heat-shrink tubing.

There is a hole and rubber grommet just to the passenger side of the transmission ground strap chassis connection. There is a hole and grommet at the front of the tunnel under the passenger floor board that goes in the smuggler’s box and another from the box toward the steering rack.

The rear of the pipe is almost straight but the front bends to the passenger side. I fed it in from the front and then bowed the entire length slightly when installing it in the rear hole.

I welded two tabs on the front suspension cross member to hold the rubber mounts for the MFI electric pump mount bracket. (I have LWB front suspension but that won’t change anything.) The OE brackets for the ’69-’70 911E&S will work fine also. The electric pump is readily available. You can snake the wires past the brake fluid supply hoses in the rubber grommet or make a new little harness. You need switched power at the fuse panel and use the nearby ground stud. Be sure and use the proper polarized electrical connector (it is common to most 911s, 914 and more.)

The return connection to the fuel tank uses the drain plug in the original configuration. You will need the pipe/banjo fitting and the banjo bolt to replace the drain plug.

Between the firewall (near the torsion bar tube) and the fuel filter console I would use continuous hose through the gap between the shock cross mount and the firewall. You should insulate these hoses with Areoquip “Firesleeve” or equivalent as they pass next the waste heater air outlet.

Everything in the engine compartment fits. The fuel filter console mounts with three rubber cylinders expanded in holes in the inner fender (be sure and use the ground wire for the console). You will need to trim away about 5” of the upper flap of the engine seal to clear the MFI pump belt protective tin (leave the lower flap undisturbed) and flatten the steel that grips the seal. The OE connections for the oil temp and oil pressure will work just fine (be sure and use the temp sender from a SWB so the gauge will read correctly.

With a powerful engine you are going to need additional engine cooling. The first line of defense is the 1.82:1 engine fan ratio. If/when you install a front cooler, use the ’74-> 911, SC, Carrera hard pipes and thermostat. You can make good (Factory appearing) hoses that go up and over the tire in the fender to come from the engine and return to the tank.

I used a ’69 only main engine wiring harness. It fits a SWB for the B+, voltage regulator and alt warning light. I used the ’69 only separate MFI wiring and made a panel for the RPM transducer, cold start relay that mounted on my Delta MK10B behind the MFI pump.

I have done several using a ’70-’73 relay panel and modified it to not damage or change the chassis wiring harness (a better way to go).

I used a type 911 transmission with a 225 mm pull-type clutch (Big clutch, 915 LSD, short gears.) I made adaptors between the 4-bolt, 2-pin flanges and the small 6-bolt SWB Lobro CV joints. The ’70-’71 clutch cable fits. I rebuilt my pedal assembly about then and used a clutch shaft from ’69 or ’70 that was longer lever than my ’68. You have to use the over-the-transmission engine oil out hose with this.

When I do this again with another 2.8S, I will use two new fuel pipes through the cockpit with Porsche screw-on fuel fittings and use the ’70-’73 relay panel.


John, the tunnel to transmission issue is when trying to install a 915 in a SWB. The return restrictor is academic but I would still like some documentation.

My ’68 911 may not be absolutely original but it has the ability to be there again with its original front suspension and mostly unmolested engine & trans.

Best,
Grady

[304065]

Ahh, the Maestro speaks. Grady knows more about these cars than practically everyone so heed his advice-search here for some cool shots of his '68.

On the return line issue, the original question was is a restrictor needed? Answer: no, my MFI 911E runs just fine even though every fuel hose in the car has been replaced by Aeroquip. The lines go from the fuel cell in the trunk into the tunnel, exit the tunnel and connect to the MFI filter console, and then return from the console all the way to the fuel return fitting on the cell, no seams. You have to move a vise close to the car to put the fittings on the hose, but it's definitely worth it not to have any connections where you can't see them. Grady was extremely prudent to make all his connections OUTSIDE an area where fuel could puddle if the line were punctured in an off.

[MikeDL]

Grady, as usual -- you've provided an amazing guide to what I'm thinking of attempting. There probably aren't many (smart) things to do with these cars you haven't already done! I'll work through all these steps as I try and figure out if this is a good idea for my car.

John thanks for the restrictor experience -- I'd hate to have to try and track down yet another piece of unobtainium for this car.