Return line fuel restriction?

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Hallzy

Hallzy

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I've been doing some reading and cannot seem to find a straight answer..if there is one.
Plumbing in my fuel system: from the tank I have 3/8 to 8an through 100 micron filter holley black pump 140gph through regulator then 35 micron filter to carb. On the return is where my question lies I have 8an back to the tank but the return at the tank steps all the way down to 1/4" is this restriction going to cause problems?? This will be feeding a 500" 643hp engine.
Thanks in advance for your input and help.
 
It could, maybe. General consensus from "experts" (which I am not) is that you want to run a return line the same size as the supply line. I also endorse putting the regulator in the return line. That way, it controls pressure in the entire system.
 
I suppose I can give it a try and see how it acts.
Or I could just cap that dinky return line and run the return into a bung in the filler neck or something.
 
The filter after your regulator could be an issue. I prefer to have regulator be the last restriction before carb.

If you step down the return line, you may experience pressure creep from that restriction.
 
I would say "yes." You are talking about the factory 1/4" tube? THAT WAS NEVER a return line and never meant for such. It was the TANK VENT on those cars that used evap controls and of course therefore limited evaporation "of the vent."

Real world: I brazed a 1/4" tube into my 67 tank when I installed a Wix return filter has an orifice for vapor lock prevention. I later used that tube for the first EFI, the little Holley TBI setup, and it FOR SURE caused some pressure restrictionin the return.

Somewhere I've read that you want the return same size or larger than supply side. Part of the reason is that it is lower pressure, and therefore hasn't as much driving force for flow
 
67Dart273 said:
I would say "yes." You are talking about the factory 1/4" tube? THAT WAS NEVER a return line and never meant for such. It was the TANK VENT on those cars that used evap controls and of course therefore limited evaporation "of the vent."

Real world: I brazed a 1/4" tube into my 67 tank when I installed a Wix return filter has an orifice for vapor lock prevention. I later used that tube for the first EFI, the little Holley TBI setup, and it FOR SURE caused some pressure restrictionin the return.

Somewhere I've read that you want the return same size or larger than supply side. Part of the reason is that it is lower pressure, and therefore hasn't as much driving force for flow
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My tank has the vent at the top above the sending unit also 1/4" but is part of the tank rather than the sending unit. What I am talking about is indeed the return line to the best of my limited knowledge.
 
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Hallzy said:
My tank has the vent at the top above the sending unit also 1/4" but is part of the tank rather than the sending unit. What I am talking about is indeed the return line
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Screenshot_20221014-145921_Chrome.jpg
 
^^OK that there is such a short section that "I bet" if you immediately bushed that up to 3/8 you'll be fine. It would not hurt to trim it down to minimal length inside and outside the tank. Also keep in mind that tube is smaller than hose, I'm sure you know that!!

You can easily measure restriction, just put a tap in right at/ after the regulator return fitting

As a former HVAC mech, I've always liked 1/4" flare Schrader valve fittings for test ports. They are of course very common in HVAC and there are lots of configurations plus "an old set of hoses" are fairly easy to drum up. If you use regular hex head flare caps instead of the "finger caps" they are very secure
 
67Dart273 said:
^^OK that there is such a short section that "I bet" if you immediately bushed that up to 3/8 you'll be fine. It would not hurt to trim it down to minimal length inside and outside the tank. Also keep in mind that tube is smaller than hose, I'm sure you know that!!

You can easily measure restriction, just put a tap in right at/ after the regulator return fitting

As a former HVAC mech, I've always liked 1/4" flare Schrader valve fittings for test ports. They are of course very common in HVAC and there are lots of configurations plus "an old set of hoses" are fairly easy to drum up. If you use regular hex head flare caps instead of the "finger caps" they are very secure
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I was intending to use a 3/8 tubing to 6an connector and then step it up to the 8an.
I will put the last filter before the regulator and give this a try hopefully it works.
 
The other thing you might consider...........

Is this a new /unused tank? I mean that would remove the danger of welding. Can you silver braze?
 
The length of the lines also affects restriction. Look at the instructions for the Mallory #4309 reg.
If you want to sleep well, make sure your return line is one size bigger than the feed line. That way, the reg spring maintains even pressure, not line restrictions.
 
Silver braze is pretty easy. Like soldering clean it well use proper flux. What I was thinking is that with a new tank you could silver braze an AN fitting into the thank near the sender hole. That hole will of course give you access.

Harris Safety-Silv 56 Brazing Kit 56KPOP

This might seem expensive but it's darn handy to have around. As a former HVAC guy I used that occasionally. Silver braze flows well, a lot better than brass, and doesn't require quite as much heat. I always used oxy-acet, but I'm told you can get by with something like a MAPP torch
 
67Dart273 said:
Silver braze is pretty easy. Like soldering clean it well use proper flux. What I was thinking is that with a new tank you could silver braze an AN fitting into the thank near the sender hole. That hole will of course give you access.

Harris Safety-Silv 56 Brazing Kit 56KPOP

This might seem expensive but it's darn handy to have around. As a former HVAC guy I used that occasionally. Silver braze flows well, a lot better than brass, and doesn't require quite as much heat. I always used oxy-acet, but I'm told you can get by with something like a MAPP torch
Click to expand...
Doesn't sound like a bad idea if going that route maybe I should put another fitting down low on the tank for pump feed and do away with the sending unit altogether seems the only thing they do well is read fuel level inaccurately
 
Hallzy said:
Doesn't sound like a bad idea if going that route maybe I should put another fitting down low on the tank for pump feed and do away with the sending unit altogether seems the only thing they do well is read fuel level inaccurately
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qast f.i. said , a 1 size smaller is adequate, mine is -06 , feed is a -08 , no problems <4 yrs...
and . a 3/8'' line is adequate at 43# of pressure for 700 h.p.
A WELL KNOWN BIG WEDGE BUILDER EVEN SAID THE SAME THING !
 
By the way "we used to" and some still do call this "silver solder" which is INCORRECT, especially now you have low temp "non lead" solder for both mechanical, plumbing, and electronics. I used non lead silver solder at the wheel chair joint for electronics work.

So the proper term is "silver braze" or high temp silver
 
Since the tank is new I would just weld a bung next to where the sender goes in and cap the 1/4.
 
I'm thinking this may be the easiest answer has anyone used a fitting like this rather than welding or brazing to attach bungs into a fuel tank? Nutsert style 6 an better than 1/4" at least

Screenshot_20221015-124133_Chrome.jpg
 
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Hallzy said:
Doesn't sound like a bad idea if going that route maybe I should put another fitting down low on the tank for pump feed and do away with the sending unit altogether seems the only thing they do well is read fuel level inaccurately
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You don't want the "intake" at the very bottom of the tank. It'll end up sucking up too much garbage. That's why the OEM "sock" sits about 1/4" off the tank floor. Ever pull an old gas tank and look inside it? You willl not believe how much crap collects in the bottom of them.
 
Hallzy said:
I'm thinking this may be the easiest answer has anyone used a fitting like this rather than welding or brazing to attach bungs into a fuel tank?

View attachment 1715998377
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I have also found a nutsert style made that looks like a good solution
69_340_GTS said:
You don't want the "intake" at the very bottom of the tank. It'll end up sucking up too much garbage. That's why the OEM "sock" sits about 1/4" off the tank floor. Ever pull an old gas tank and look inside it? You willl not believe how much crap collects in the bottom of them.
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For sure my old tank had lots of **** in the bottom
 
Hallzy said:
I'm thinking this may be the easiest answer has anyone used a fitting like this rather than welding or brazing to attach bungs into a fuel tank? Nutsert style 6 an better than 1/4" at least





Lesson learned don't buy these things everyone they are absolute garbage bolt straps right out of the aluminum and doesn't even com close to being tight ...let alone sealed. Oh well I tried and it failed so I cut it off and welded on a proper 8an male bung problem solved.


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Hallzy said:
I've been doing some reading and cannot seem to find a straight answer..if there is one.
Plumbing in my fuel system: from the tank I have 3/8 to 8an through 100 micron filter holley black pump 140gph through regulator then 35 micron filter to carb. On the return is where my question lies I have 8an back to the tank but the return at the tank steps all the way down to 1/4" is this restriction going to cause problems?? This will be feeding a 500" 643hp engine.
Thanks in advance for your input and help.
Click to expand...
The only truly correct way to do this is to run the same size lines, fittings, everything from and to the tank. -6AN is pretty adequate for almost anything under 600 HP. Pickup in the tank if you can using an in-tank pump. Otherwise use an external pump near the tank, mounted lower than the pickup so it siphons naturally. Run that line to a good filter, near the engine. Then the filter output goes to an adjustable bypass fuel regulator. One (or two) output lines from the regulator go to the carb or EFI. Then you run a line from the return port of the regulator back to the tank. I have run this setup with both EFI and with a carburetor and it works great. I'm using a Tanks, Inc. 60 psi pump in the tank, and a Aeromotive Universal Bypass Regulator #13301, which is one of a very few that can be run with a carb or EFI (3 TO 65 psi). This is a key component to building a good reliable system, so don't buy a cheap regulator!
 
69_340_GTS said:
The only truly correct way to do this is to run the same size lines, fittings, everything from and to the tank. -6AN is pretty adequate for almost anything under 600 HP. Pickup in the tank if you can using an in-tank pump. Otherwise use an external pump near the tank, mounted lower than the pickup so it siphons naturally. Run that line to a good filter, near the engine. Then the filter output goes to an adjustable bypass fuel regulator. One (or two) output lines from the regulator go to the carb or EFI. Then you run a line from the return port of the regulator back to the tank. I have run this setup with both EFI and with a carburetor and it works great. I'm using a Tanks, Inc. 60 psi pump in the tank, and a Aeromotive Universal Bypass Regulator #13301, which is one of a very few that can be run with a carb or EFI (3 TO 65 psi). This is a key component to building a good reliable system, so don't buy a cheap regulator!



Sounds like exactly what I have done
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