MFI Fuel System Re-Engineering Questions

[304065]

Ladies and Gentlemen:

I have all the stuff on order to convert my stock '71 E MFI fuel system to -6AN Aeroquip. This is harder than it seems: the stock bosch pump won't accept a -6AN fiting, so I'm adding a mallory fuel pump and return style pressure regulator- to be mounted up front next to the fuel cell. -6AN hardware everywhere, all the way back to the stock filter console. -6AN to 14mm x 1.5 thread banjo fittings for the filter console are about $15 apiece and you need FOUR of them. . . not for the faint of heart but I'm committed to making this thing look like an ICBM when I'm finished.

Does anyone know where the fuel pressure should be measured? I saw one of Warren's posts (http://www.pelicanparts.com/cgi-bin/vb/showthread.php?s=&threadid=6546&highlight=mfi+fuel+pressure)
that suggested that you measure it in the loop between filter and MFI pump, which I suppose would be best. But for convenience, I'm thinking about putting a VDO pressure gauge immediately next to the output from the regulator, which I suppose will mean that the pressure at the MFI pump will be a couple pounds lower due to friction etc. Anyone BTDT?

One more question, in the lines entering the fuel filter console, the straight fitting for the return line has an integral check valve. I suppose the purpose of this is to keep fuel from flowing backwards through the system?

[Roland Kunz]

Hello

I'm thinking about putting a VDO pressure gauge immediately next to the output from the regulator, which I suppose will mean that the pressure at the MFI pump will be a couple pounds lower due to friction etc

Wich regulator ?

Pressure lower due friction ?

F.E.: If a submarine merges fast trough water the pressure on it will be lower due friction ?

[304065]

Roland,

I'm installing an aftermarket fuel pump, a Mallory, which requires the use of an external fuel pressure regulator. I'm going to plumb in a -6AN male-to-male fitting that has an 1/8" NPT threaded hole in it, and mount a VDO pressure sender and electric gauge in the cockpit. By adjusting the spring on the aftermarket fuel pressure regulator to 1 BAR, I should be able to generate the appropriate pressure in the "loop" between filter and MFI pump.

When fluid supply systems are designed, the designers often incorporate sweeping 90 degree elbows that have a much larger radius than a sharp 90 degree "T" fitting- the reason is that the fluid pressure decreases over the distance due to friction from the fluid having to make sharp corners, given a constant force pushing on it and assuming an incompressible fluid. By making gradual turns, there's also less turbulence which inhibits flow.
But considering that I'm only going about 5 meters back to the MFI pump, the pressure drop will be negligible.

But enough theory: any advice on how I can run the stainless aeroquip lines through the tunnel, where the factory hard lines are currently? I want to run them through the tunnel, inside the internal channel for the current lines, so they won't hit the shifter.

I am anticipating multiple lacerations to the hands.

[Roland Kunz]

Hello

Just to make it clear a carburator fuelpump will not work and moste EFI Pumps will also not work on the MFI systems.

The pump must deliver 2L per minute at 1 bar pressure. The fuelines are some 2,5 meters on both sides ( feed and return )

Porsche avoided sharp turns in the system.

I can´t see a reason to use rubberlines ( Even if they are braided stainless ) in the tunnel replacing the hard pipe lines.

If you miss them or they are brocken, rustet or what ever then get some adequade pipe materiel and resape the originals.

You also can go to use the 3,2 Fuelines ( need some slight rebending as the seatbucket changed over the years.

Mount the fuelpump to the later used position on the crossmember from the steering/axle.

You can messure the pressure atop the filterhousing where the selenoid for the coldstartvalve sits Just add a tee showing forward and backward.

Replacing the rubber lines with braided steel hose ain´t a big problem. If you use Ring ends with hollow screwsn on the fuelfilterhousing you can save some bucks.

Aeroquip has some nice fast couplers with viton seal.

Two of them makes things easier on enginework.

I would go to aluminium fittings and light teflon housees with Nomex ( fire preventing ) braided sleeve ( They are some 70% lighter then the normaly used stainless steel braided hoses) and the dash 6 versions withstand some 200 bar burstpressure and runs 50 bar pressure for sure.

Leave that shiny stuff to the posers. ( You know those american engine dress up kits ? )

Grüsse

[304065]

Roland,

Thanks for your thoughful reply.

2 L/Min at 1 Bar press. . . converting from metric . . .

[2L/Min = .528344 US Gallons/Min = 31.7 US Gallons/Hour

1 Bar = 14.5038 PSI]

So, the pump must deliver a minimum of 32 GPH at 15 PSI.

The pump I have chosen is a Mallory Comp Series 60FI. This pump will flow approximately 58 GPH at 15 PSI. So, this should provide an adequate operating margin of 181% of required capacity.

I have obtained a Bosch relay socket and fuel pump relay, and will run a 10 amp circuit breaker, toggle switch, and inertia fuel cutoff switch in series with the pump.

My rationale for converting to all braided stainless lines is a reduction in the number of junctions. Like in wiring, where the greatest likelihood of failure comes not from the middle of a wire but from a connection, I think the greatest likelihood of a leak comes at the connections. So, I went with braided stainless aeroquip hose with aluminum compression fittings, and have run the fuel lines from the fuel cell, to the smuggler's box (the fuel pump is mounted on the front side of the box, then two continuous lines from the pressure regulator, into the tunnel (through the circular vent for the old Webasto heater) then through the tunnel and through a hole in the panel under the seats, near the shift linkage/throttle. Where the lines pass through this panel, I have run them through PVC tubing for abrasion resistance. I decided NOT to use bulkhead fittings there because of the likelihood of a leak developing undetected. Then they run through firesleeve up to the engine compartment, through the hole where the vapor purge hoses passed (all vapor purge hoses have been removed) and end at the 14MM x 1.5 fittings on the fuel filter console.

I did not want to use clamps to attach to the factory hard lines: while very strong, it would be hard to "bead" the lines in place on the car, and impossible to get a flaring tool onto the ends. Also, I was concerned that the rubber grommets that hold the lines were old and brittle.

I like your idea about the quick-disconnect couplings, I will consider them if I anticipate dropping the motor frequently.

Thanks for your suggestions, I will post some photos of the completed installation.