Help!! Fuel Line size recommendation
 

I have read several posts on fuel line sizing and I am just running out of time and need to order components tonight to have my car back together for a planned cruise this coming weekend. I have mounted my dual feed line at the carburetor so that the input is located to the rear of the car. I cut the factory steel line approximately in line with the firewall and ran a braided stainless steel fuel line to the carb. The problem is the factory line measures .400 outside diameter. The 6an tube to hose fitting is made to fit on a .376 give or take outside diameter steel line. I talked with an AN manufacturer fitting rep and he stated they do not have a fitting to fit my factory steel line. He did make the suggestion since my factory steel line was thick was to try sanding the line to fit. After hours of sanding while under the car I got the fitting cap and ferrule to fit over the line. Well, when I tested the fuel line not surprisingly at all the fitting leaked. Before anyone asks the compression joint was tightened a quarter turn upon contact of the ferrule as recommended by the rep. Now my questions. I will be running a stainless braided fuel line from the pump to the carb. My current fuel line arrangement although not been driven is as follows: Factory 3/8" rubber hose from tank to 100 micron holley filter with 3/8" npt and barbed fittings, 3/8" rubber hose to Holley 12-150 150gph HP series electric pump with 3/8" npt and 3/8" barbed fittings in and out, 3/8" rubber hose to factory steel 3/8" line to firewall then 6an tube to hose fitting, summit 40 micron fuel filter, 6an steel braided hose to 6an dual feed line at carb. My engine is a 445 cu. in. KC small block dynoed at 611 hp at 5900 rpm with 750 carb. The carb was used on a 408 and felt a little weak and went to a 850 and achieved better performance. My question is since there may be a possibility of tracking my car. Should I upgrade using 1/2" or 8an fittings including the dual feed at the carb. I've done short spirited runs with no fuel starvation issues but my concern would be will the 6an line be capable of supporting longer high speed runs. I prefer to stay with the 6an as I have just purchased many new components. If the suggestion is to go to 8an has anyone experienced dropping the SPF tank and what will be required to increase the pick up line? Not afraid of fabrication. Thanks in advance!!

I personally would run a -8 from the tank to the pump, and the pump to the regulator, then you can run -6 lines from the regulator to each bowl.

i would run no. 8 line, did that on mine, mine dyno at 547 hp, had no problem with fuel starvation, running a holley blue pump

Okay, so one part of my information was incorrect. I have a Holley 12-125 125 gph electric fuel pump with maximum pressure of 7psi. So no external regulator was required. These pumps use 3/8" npt fittings. Without a fitting in front of me to check inside diameter will this be okay using 3/8" npt female with 8an male ends or do we create a restriction? For now so I can get rolling is to plumb from the output of the pump to the carb with 8an steel braided hose and replace my dual feed carb line with a 8an in lieu of the 6an presently on the motor.

I have a -10 pickup with all -8 lines except from the front regulator to the carb (x2), which are -6.

Are you running a return line?
 

Pman1961 I race 98% track and run 2 systems of pumps, filters and check valves. I only run 1 pump at a time unless needed. Backup plan.
#8 or #10 line is the best way to go. better to have too much supply than running lean on long runs. Wrapping and or shielding the lines from tank to the motor is also needed. Clamp the lines to the frame every 12" to stop vibrations.
Rubber hose keep to minium because of the ethohol in the gas eats rubber over time from the inside out. Takes about 8-10 years for failure, repaired twice between fuel outlets and fuel pumps.
I would recommend a pressure regulator of 6 psi with a #6 return line to the tank. This will pervent vapor lock when racing.
Put an electric fuel pump as close to the fuel cell or tank as possible. Some of these pumps don't have good vacuum. If you are going to race, get a fuel cell that is SEFI aproved.
Better to have more than is needed, then not enought when running.
Also look into running marine 4" fans under the hood to help remove hot air in the motor bay. Simple hookup with 2 plates to locate fans and blow air out louvers on front fenders. It helps alot and knocks down the temp about 20-30 degrees. Good luck. Rick L.

I run #10 from an aeromotive A1000 in tank pump to a Y, where I split to two #8 lines feeding each bank. The return line is #8. Never seen a problem. If I were you, I would go to #8 from the pump and put a regulator as Rick suggested and then use #6 for the return. Do not worry about the #8 line being bigger than your pump fitting ID. Resistance to flow is as much driven by length as diameter. You do not want a long line to be the same ID as some short length fitting.

I've been googling and reading up on the advantages of a return line system, hp pumps with external regulators. It seems as though the pumps are running full speed and when there is less demand of fuel it creates a deadhead situation, cavitation, more heat, reduced life of pump. With a return line system the excess fuel gets pumped back into the tank. My question is and I must admit I have not researched as I'm working on the car and am hoping for an answer this evening checking on comments. Do internally regulated pumps go one speed and one speed only if it states maximum pressure of 7psi? I know when you turn the ignition on you can hear the pump change tones when the fuel system is fully primed so I would assume it runs full speed at all times. Yet what is happening to the fuel in the pump if not needed at the motor? Is the pump chopping away at the fuel in the pump or is something else going on that I'm not aware of? Again, I need to do a little more reading but does the return line need to come off the regulator or can it be elsewhere on the fuel system or do some pumps have a return line output? Again, apologize for not doing my home work. Just a lot going on and looking for people that have been there and done that to respond. Thanks.