[Skip Fix]

I know ideally below the tank but my street 78 elective is not and runs high 10s with a stock pickup.
Fitting it so I did not think it would hit the rear pumpkin as it moved up and down and clear exhaust tailpipes and finding a flat spot on the trunk floor to bolt it to. It is on the driver's side with fuel lines running to passenger side-normal for a Chevy and the side a Holley takes anyways.

Tank has a sump and a pre filter to pump then a System 1 halfway under passenger seat on the carb side to regulator.

I heard the Mallorys can be mounted almost horizontal as they have some vent slots if they leak. The new Holley pumps mount sideways.

[grandville455]

Yea I hear ya, Good thing for me is I have a cell so the pump doesn't have to hang so low like if i had a sump in stock tank etc. I think i remember reading that about mallory's also being ok to mount sideways.

[vidguy]

So I have a question. If the outlet of my sender is 1/4 NPT, does hooking that to an -8an (1/2") or larger line allow the fuel to flow to the ability of the larger line?

At what point does the minimum inside diameter of an orifice or tube matter? When does it restrict flow? At the "END" of the line, but not at the beginning?

Looking at Skips pictures. I have my Tanks Inc tank and sender with a 1/4 NPT fitting on both send and return.

I have started to set this up. On my Send I was going to use a 1/4 NPT to 3/8" barb fitting to 3/8 Twistloc line for the first 2 feet for flexibility, to the -8AN fitting on the rear end of the 1/2" stainless line going forward.

I considered using a 1/4 NPT to 1/2 barb and 1/2 TwistLoc line but I thought that if the fuel was coming out of a 1/4 fitting as long as all of the tubing after that was LARGER than 1/4", (the minimum restriction in the path) fuel would flow to the ability of the LARGEST tubing (the 1/2" inch) so whether the first 2 feet of line was 3/8" or 1/2" line after the initial 1/4" fitting, it would make no difference. Am I wrong?

On my RobbMc Regulator, in bypass mode, the fittings for fuel coming and going to the carburetor are 3/8" NPT. Why run a 1/2" line to it if the 3/8" will restrict flow?

Is the factor you are concerned about the length of the restriction? Where in the Robbmc, or my sender, the very short 3/8" or 1/4" passage has no real effect?

[Tom Vaught]

Originally Posted by vidguy

So I have a question. If the outlet of my sender is 1/4 NPT, does hooking that to an -8an (1/2") or larger line allow the fuel to flow to the ability of the larger line?

At what point does the minimum inside diameter of an orifice or tube matter? When does it restrict flow? At the "END" of the line, but not at the beginning?

Looking at Skips pictures. I have my Tanks Inc tank and sender with a 1/4 NPT fitting on both send and return.

I have started to set this up. On my Send I was going to use a 1/4 NPT to 3/8" barb fitting to 3/8 Twistloc line for the first 2 feet for flexibility, to the -8AN fitting on the rear end of the 1/2" stainless line going forward.

I considered using a 1/4 NPT to 1/2 barb and 1/2 TwistLoc line but I thought that if the fuel was coming out of a 1/4 fitting as long as all of the tubing after that was LARGER than 1/4", (the minimum restriction in the path) fuel would flow to the ability of the LARGEST tubing (the 1/2" inch) so whether the first 2 feet of line was 3/8" or 1/2" line after the initial 1/4" fitting, it would make no difference. Am I wrong?

On my RobbMc Regulator, in bypass mode, the fittings for fuel coming and going to the carburetor are 3/8" NPT. Why run a 1/2" line to it if the 3/8" will restrict flow?

Is the factor you are concerned about the length of the restriction? Where in the Robbmc, or my sender, the very short 3/8" or 1/4" passage has no real effect?

I will try to give my opinion on some of your questions:

1) the 1/4" NPT to 3/8" barb fitting connected to your 1/2" fuel line would be the 'RESTRICTION' to the system if the system was designed like a factory system with a forward mounted fuel pump "sucking" (creating a negative pressure) on the fuel system.

2) In would case you have a Tanks, inc fuel system with a fuel pump inside the tank that can PRESSURIZE the fuel passing thru the 1/4" NPT to 3/8" barb fitting to 42+ psi of fuel pressure thru the 1/4" NPT to 3/8" barb fitting before it gets to the 1/2" fuel line.

3) The 1/2" fuel line, being filled full of fuel now sees 42 psi on one end of the line and tries to pass fuel being pushed at 42 psi thru the length of the line (minus wall friction from the hose of metal lines). The volume coming out of the pump would remain the same as the 'RESTRICTION' to the system is still the initial 1/4" NPT to 3/8" barb fitting as well as the outlet diameter nipple of the pump itself. The 1/4" NPT to 3/8" barb fitting would be the actual 'RESTRICTION' to the system' if you were running a dual fuel pump deal where the pump capability was higher than the 1/4" NPT to 3/8" barb fitting could flow.

4) So the 1/2" line does little for you move the fuel at a given rate thru the larger conduit.
It you are pushing 1 quart of fuel thru the line at one end (or marbles) if 50 marbles pass thru one end of the hose in a minute, then 50 marbles come out the other end of the hose in a minute. BUT if a dual pump could push 100 marbles thru the hose and the hose becomes the restriction then the hose needs to be larger. A 1/2" hose can pass a lot of 'marbles' when two pumps are pushing at 40+ psi of fuel pressure.

5) Then the engine consumes a given amount of fuel.

6) If the consumption rate is low then a lot of fuel has to pass back to the tank or the pressure is too high to the carb or fuel injectors. As the pressure will be lower in the system, you need a given diameter line that will return enough fuel so that you can maintain the fuel pressure at the carb or fuel rail system. 6 psi at the carb or 39-42 psi at the fuel rail. If it takes a even larger fuel return line to pass the fuel back to the tank then that is what you need.

7) Last point, If the fuel return line is 1/2" and the fitting going back to the tank is a 1/4" NPT to 3/8" barb fitting, but the return system pressure is lower then how can the return filling not be a restriction in the line? So you may be able to use small fitting and a high pressure pump to push fuel but a large fitting to get the fuel back in the tank or your big return line does nothing at low speeds. At high speeds the engine is using the fuel so there is very little return fuel going back to the tank thru the fitting.

So you need to optimize the return line/fittings for IDLE conditions and the feed lines and fittings/fuel pumps for WOT conditions.

Tom V.

ps if you are pumping fuel from the tank to a Robmac surge tank deal then you basically are using the stock tank system to keep the surge tank system filled with fuel (that is not already recirculated by the surge tank system).

[vidguy]

Thanks for the clear explanation. Especially regarding the suction or pushing effect Tom. Much Appreciated.