return line for EFI conversion

[R3dplanet]

Hey everyone. Thanks for the excellent responses. I finally settled on using new 3/8" stainless lines to and from the fuel tank. At least, I think I am. I discovered Swagelok fittings, and now my eyes are open.

Pishta, I'll certainly look into the NAPA filter set up. I was all set to get an Aeromotive pre-filter and post-filter, but now I'm curious about this new setup that requires to major return line. I'll think about it.

Roger, are you using the stock GM TBI computer with PROMs? I've been bench testing my Megasquirt 2 v.3 computer all week with great success. I'm ready to bolt it up and start tuning once I get the plumbing sorted out. But it's super cold out, so this might have to wait until Spring.

-marcus

 

[jbc426]

I'm in the middle of installing a 3/8's feed and return line for a carb to EFI conversion on my '68 Barracuda. I'm installing a 2000 5.9 out of a Dodge Durango with the factory EFI. I used a 98 Ram truck 5 speed computer with Hotwire auto's Hotrod wiring harness and am going to reflash the computer with an SCT Tuner programmed by Scott at Hemifever.

Anyway, I ended up removing the 1/4 inch return line fitting on a replacement 3/8's sending unit and replaced it with a similar shaped piece of 3/8's steel line. I used silver solder to seal it up and securly attach it to the sending unit. It now looks like it came this way. I'm using 3/8's aluminum line for supply and return simply because it's a lot easier to work with and bend.

I choose to use a low-pressure electric externaly mounted lift pump that feeds a front mounted surge tank with internal high pressure EFI pump. For those not familiar with this set-up, the low pressure pump sucks fuel from the tank through the 3/8's pickup, through a canister fuel filter/water seperator and pumps it up to the front of the car (exactly like a traditional electric pump fuel system for a carbureted vehicle) where it fills up a small 1 liter surge tank that returns the fuel back to the gas tank. The pressure on this low side is very near 0 psi, but with significant volume. For this reason, it's important that the return line and tank fitting doesn't create any measurable back pressure.

The high pressure side of this fuel system starts from the internal surge tank mounted fuel pump, goes to one side of a pair of billet fuel rails and out the other, back to the surge tank, through a bypass regulator and finally back into the surge tank. The high pressure side of the fuel system is relatively short, has a full flow design and keeps the high pressure lines just long enough to feed the fuel rails and keep the surge tank safely mounted away from engine heat.

The benefit of using this method is that fuel flow to the EFI system is extremly resistant to fuel cavitation while cornering, starting and stopping etc even with a very low fuel level in the tank; and it keeps the fuel cool. It also eliminates the need to modify the fuel tank, use an internal tank mounted high pressure fuel pump or plumb high pressure fuel line to the front of the car.

I'll post some pics once I get the fuel system installed. FYI: The diagram below shows and externally mounted EFI pump. On the system I have, the pump is mounted inside the surge tank. Either way is fine, but an internally mounted pump will be quieter and run cooler.

 

[jbc426]

..........
Anyway, I ended up removing the 1/4 inch return line fitting on a replacement 3/8's sending unit and replaced it with a similar shaped piece of 3/8's steel line. I used silver solder to seal it up and securly attach it to the sending unit. It now looks like it came this way. I'm using 3/8's aluminum line for supply and return simply because it's a lot easier to work with and bend.
............

Here's a picture of the modified fuel sending unit both outside and inside the tank. You can see I attached a piece of submergable fuel line to extend the return down and away from the pick-up tube, yet still allow it to be squeezed inside the factory sending unit openning.

Obviously the main reason for doing this is to increase the size of the return line for either a traditional carburated set-ups or for a surge tank based EFI conversion system.

For EFI conversions, the cost and time to modify these parts for use with a surge tank is significantly less when compared to buying a custom tank with baffles, cutting and welding in sumps and baffles in your exsisting tank for mounting high pressure pumps inside them. Even compared to the cost of buying a pre-made surge tank.

Virtually no air is picked up by the high pressure pump mounted inside the surge tank at the front of the car even at very low fuel levels under high G conditions without any baffling in the tank. The air goes to the top of the surge tank and is almost immediatley sent back to the fuel tank and away from the high pressure pump inlet. For EFI conversion cars capable of extreme cornering and/or high horspower cars with lots of traction, adding tank baffling would only enhance the performance of this lower cost EFI conversion set-up.

 

[RogerK]

Roger, are you using the stock GM TBI computer with PROMs? I've been bench testing my Megasquirt 2 v.3 computer all week with great success. I'm ready to bolt it up and start tuning once I get the plumbing sorted out. But it's super cold out, so this might have to wait until Spring.

-marcus

Yes, with modified PROMs. I picked up 2 EEPROM's, modified them to fit into the GM ECU and burn them with the MOATES Burn 2 hardware. I use the CATS tuner program to alter the BIN files for more fuel, spark, etc.

I just worked out all the kinks and went for my 1st test drive this weekend. PM me if you have any questions.