FI Tech fuel injection fuel lines

You guys that have installed this system with a fuel pump in the tank, I've got a question. I was planing on buying a factory 3/8" supply line and either a 5/16 or even the factory 1/4". What do you think. Is 1/4" big enough?

What size line does FITech supply in their full kit ... that's the size you need !

3/8 supply 5/16 return

I'm not sure they supply lines.

This is the setup I am running on my EFI system. I am running F&B 6 pac with 500 hp. No issues.

1/4" might be too restrictive for the return?
I haven't installed the FiTech yet, but I thought I read it can control the fuel pump voltage? If it can, then the 1/4" should work, but if you can go with a larger return and run the pump constant, I think it may be easier on the pump?

Sizing the return line isn't to help the pump as much as it is to avoid overpowering the regulator. If there's enough fuel flow through the inlet and not enough out of the outlet, the fuel can "back up" in the return line and suddenly your fuel pressure goes way up.

R.

The regulator will control the flow as long as the supply and/or return lines are not too small. So if you are thinking one day you might step it up consider upsizing the lines since you are buying new anyway, assuming the cost increase isn't too stupid.

FI Tech specifies a #6 (3/8") return line.

This is the proper thing to do.

Remember that you'll be returning a pretty good volume of fuel (far more than you consume outside of WOT). Pushing that much volume through a 1/4" line means more pressure and velocity are required to get the job done.

That tiny return is like putting your thumb over the end of a water hose. Pressure is going to build up. The pump will be working hard instead of idling with a large return line.

I run an in tank EFI pump and factory style steel lines. 3/8" supply and 5/16" return. Regulation is effective and steady for 40-45 PSI fuel pressure. My current pump is a Bosch rated for 700 HP EFI. Previously I ran an Aeromotive pump rated for 1000+ HP with the same system and regulation was fine.

To make this setup I ordered two sets of fuel supply lines, 3/8" and 5/16". I customized with double flare end adapters to make connection at tank and regulator with AN braided cover hose.

With this setup, minimum fuel pressure is around 20-30 PSI due to return line restriction. Not good for a carb but fine for EFI which needs 40+ PSI.

I was reading the software setup manual, and the "Go EFI" units have a Pulse Width Modulated fuel pump driver, but it looks like it does not monitor the fuel pressure, it looks a user pre-set TPS and RPM values, that if the engine is under the specified RPM or TPS value, then the pump drivers applies a user defined PWM percentage to set the pump for a lower flow rate.

On my Coronet (Edelbrock XT EFI), I am running -6 AN hose supply and return, except for about 6" to/from the Spectra EFI fuel tank that uses 3/8" supply and 5/16" return. It only has a 225 LPH pump, but I think the line sizes would be fine even with a larger pump.

Also, they have a $100 rebate going on for the FiTech units

Thanks guys. I think I need to get the FI system before I order the lines. I also have the new tank with a pump already so I need to check those fittings as well.

Interesting note: The return -6 fitting's orifice...!

After a quick call to FITech to be sure that wasn't intentional I'd slam that thing in a collet and poke a bigger hole through it.

It's my understanding that -6AN is supposed to be 3/8" internal diameter which is .375". Not even sure you can drill that return fitting that big. What you have is barely bigger than 3/16", or -3AN.

It doesn't seem right but here goes:

Fluid does not go through a smaller opening like toothpaste squeezed from a tube. What it does is convert some of the fluid's pressure into kinetic energy, so the same amount of liquid flows through the opening, at a much faster linear velocity. Then the additional kinetic energy is converted back into pressure on the other side of the hole. Some of the energy is lost in the two conversion processes.

What the pump sees is a mathematical addition of all the flow resistances in the system. At the desired flow rate, each foot of pipe will have a pressure drop. things like valves, elbows, etc. are usually added in as an equivalent number of feet of total pipe length. Then you can calculate the total losses in the system.

The fitting in question will probably add no more than 1/4 psi to the losses in that tubing run.

There's only one time I would take the time to enlarge the fitting and that's if it was on the inlet size of the pump. One should try to eliminate all restrictions from the inlet size. That's why there should never be a filter on the inlet of any pump, just a screen to keep out the larger particles.

R.

All math aside, it's described as -6 AN, which to actually be a -6 needs a 3/8" passage.

Does it need 3/8"? I dunno, don't care as long as it works.

The nominal dimension for a common #6 AN fitting is .295".

Whenever a manufacturer specifies a certain line/hose size they are taking into consideration the fitting bore size, especially if they supply the fitting.

I had emailed Fitech about this situation back in December/January, not sure, and they said the 5/16 return would be fine. So, I went with it and yanked the original 1/4 return. Put a new 3/8 supply line and used the original 5/16 supply as the new return. Haven't experienced any issues that would indicate an issue with the return's size. Edit: Maybe they have changed their "tune", since then?


That being said, I noticed one day, many months ago, that I thought the tank was warmer than maybe it should, but haven't dealt with it, nor asked around as to what others are experiencing.

Also, in putting together my system, I did find some fittings from various manufacturers, seemed to be a bit smaller than what I thought I was getting. I made sure that if I was running a 5/16 return or 3/8 supply, that it was actually 5/16 or 3/8 (or as close as could be within reason) all the way from the pump to the Fitech.

Energy is never lost. It is simply converted into another form, usually heat.

What you are missing is the pump is stupid. It will keep hammering away and increase pressure as resistance is found. It will draw all the amperage allowed trying to keep the impeller speed up. That leads to very high pressures, cavitation, and higher fuel temperatures.

I, too, have had a return line that was too small. It resulted in uncontrollable fuel pressure. The regulator couldn't bypass enough fuel due to line restriction.

Replacing the small diameter fuel line with a larger piece cured the problem.