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 Post subject: Return line?
PostPosted: Sat May 06, 2017 6:19 pm 
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TBI Slant 6
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Joined: Tue Feb 24, 2015 3:41 am
Posts: 198
Location: South Carolina
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Is there a sending unit with return that will fit in my factory side mount or will I have to fabricate something? Any ideas or comments?


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PostPosted: Sat May 06, 2017 11:51 pm 
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Joined: Sat Feb 08, 2003 2:37 pm
Posts: 4124
Location: CA
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I brazed a nipple on mine. Later on I stumbled upon this idea I would have rather done. Drill/tap the filler neck for npt thread. Install hose barb, to hardline, through the trunk floor (or filler tube gasket?). Or could use an npt > flare fitting and flare the hardline if your worried about a rubber line leaking. Once your below the trunk floor you can use another section of hardlline to make install easier.


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 Post subject: Re: Return line?
PostPosted: Sun May 27, 2018 4:41 pm 
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Turbo EFI
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Joined: Wed Nov 23, 2011 11:07 am
Posts: 1938
Location: SF Bay Area
Car Model*: 67 dart 2 door hardtop
Not sure I understand, the sending units for mopars come in two flavors, one with a return line, one without.

b

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 Post subject: Re: Return line?
PostPosted: Tue May 29, 2018 1:27 am 
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Location: CA
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Those are usually 1/4". Plus I never had luck getting new senders (even the mopar branded ones) to read right on the stock gauges.


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 Post subject: Re: Return line?
PostPosted: Tue Jun 05, 2018 1:30 pm 
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TBI Slant 6

Joined: Sat Nov 12, 2011 10:04 am
Posts: 193
Location: Upper So. CA
Car Model*: '65 Valiant 170 T5
I got one from Rock Auto that has a 3/8" supply and a 5/16" return, and no it doesn't quite work right with the '65s gauge, but its close!

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 Post subject: Re: Return line?
PostPosted: Tue Jun 05, 2018 6:11 pm 
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Supercharged

Joined: Thu May 12, 2005 11:50 pm
Posts: 5817
Location: So California
Car Model*: 64 Plymouth Valiant
DON'T HOLD YOUR BREATH...………

I may come up with a solution for the gauge reading problem.

Fairly soon I'll be getting a new sending unit. (and tank).

Depending on complexity, I was thinking of making a electrical (analog, transistors, resistors) translator black box to give the gauge what it wants to see for various levels in the tank.

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64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes
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 Post subject: Re: Return line?
PostPosted: Thu Jun 07, 2018 10:15 pm 
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Joined: Wed Nov 06, 2002 1:57 pm
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Location: Everett, WA
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i welded a bung into the filler tube and used that for the return line. Works good.


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 Post subject: Re: Return line?
PostPosted: Sat Jun 16, 2018 5:37 pm 
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Turbo EFI
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Joined: Wed Nov 23, 2011 11:07 am
Posts: 1938
Location: SF Bay Area
Car Model*: 67 dart 2 door hardtop
If your current sending unit is reading correctly, then yes, the guys who are saying put a return line into your filler tube are correct that is an easy option and you won't get one of those newer sending units that doesn't correlate well with the factory gauge.

I also note that I've taken one of those newer ones apart and played with (bent) the contact that rubs on the winding in the rheostat, to make it read more closely to what is in the tank. It works, but the problem is that they are built so cheaply that it doesn't last long. Again, if your current sender is reading correctly and you simply want a return line, then I would suggest one of two options.

1. you can run a return line to the filler tube as suggested. One said they brazed a nipple into the filler tube. Personally, I've simply run the return line to the vent on the filler tube and it worked fine. This requires running your return line up into the trunk, drilling a hole through the trunk floor somewhere.

2. I've also installed a nipple in a factory sending unit. You have to measure where there is sufficient area to install a nipple and not interfere with the sending unit arm that moves and also not interfere with the installation, particularly the rubber seal, of the sending unit. This does not require running the return line through and into the trunk.

Brian

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 Post subject: Re: Return line?
PostPosted: Sun Jun 17, 2018 7:21 am 
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TBI Slant 6

Joined: Sat Nov 12, 2011 10:04 am
Posts: 193
Location: Upper So. CA
Car Model*: '65 Valiant 170 T5
In some cases the Ø5/8" rubber fill neck vent hose is long enough that it can be made into two shorter pieces of hose and a section of tube with a return fitting can be installed in between. This wouldn't work on my '65 Valiant, but it will work on my '70 Bronco. No familiarity with later models so I mention it just in case that is an option.
https://bcbroncos.com/shop/fuel/efi/11- ... rd-bronco/

There is also reportedly a similar part made by someone that does the same thing with the filler hose, but I've not been able to track down the vendor. If you've tools this would be a simple part to make.

I have also read of guys simply drilling and tapping the fill neck, and then screwing in a hose barb to NPT 90° adapter. Some say to put this up pretty high on the neck and others caution to place it where a fill nozzle won't back-fill it. Not sure how important that is, but just for GP I'd avoid this if possible.

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 Post subject: Re: Return line?
PostPosted: Sun Jun 17, 2018 12:25 pm 
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Joined: Thu Jun 04, 2015 6:19 pm
Posts: 160
Location: Florida
Car Model*:
I'm not a fan of a constant return line above the fuel tank level, constantly aerating my fuel. Not sure how much of an issue that is, both in aerating, and helping to separate the lighter fuel aromatic hydrocarbons. I would seek a different solution. I'm also in South Fla, I don't need any extra help evaporating my fuel. :D


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 Post subject: Re: Return line?
PostPosted: Sun Jun 17, 2018 12:49 pm 
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Joined: Sat Nov 12, 2011 10:04 am
Posts: 193
Location: Upper So. CA
Car Model*: '65 Valiant 170 T5
the return line should be above the fuel level in the tank. The reason why is that any restriction to flow changes the pressure at the injectors. If the return is below fuel level then it will have a head on it that varies with fuel level, so injection pressure will also vary with fuel level. Not by a lot, but why introduce a variable when you don't have to?

The better return lines don't just drop the fuel in straight from above and thus entrain air in the fuel, they spray it out in a way that minimizes this. One way is to use a 90° bent tube in the inside of the pick-up assembly with the last leg of the 90° oriented horizontally. I think that I recall that the pick-up that I bought from Rock Auto has this feature, though the the front wall location of the assembly I'm not sure why. The various fill tube options for adding a return are also good in that the fuel condenses on the far wall of the tube while falling back into the tank.

If you want to get really anal about not entraining air in the fuel take a thorough look at how dry sump oil tanks are designed to avoid this. Getting the air out of engine oil is a lot harder than getting it out of fuel, but the principles still apply. There is a very good reason why the best dry sump oil tanks are round.
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 Post subject: Re: Return line?
PostPosted: Sun Jun 17, 2018 6:32 pm 
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TBI Slant 6

Joined: Thu Jun 04, 2015 6:19 pm
Posts: 160
Location: Florida
Car Model*:
I find hard to believe that I have never heard anyone be concerned about the flow restriction of a return line based on its length as factor in regulator operation, but a few times it is discussed about fuel return line diameter which seems like only a factor if smaller then feed line, all that being said, the max difference in "head" in a typical tank of say 8" here, is hard to fathom.
That meaning, I'm skeptical. :D

PS, "aerating" fuel was of minor concern to me in my previous reply, but thought others might focus on that aspect so I only mentioned it, the main concern was on a constant basis while pumping, at nearly full flow at low power levels, facilitating the separation of the lighter aromatic fuel components and their dissipation into the atmosphere, with the inherent loss of some useful traits, like octane, etc


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 Post subject: Re: Return line?
PostPosted: Sun Jun 17, 2018 7:42 pm 
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Turbo EFI
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Joined: Wed Nov 23, 2011 11:07 am
Posts: 1938
Location: SF Bay Area
Car Model*: 67 dart 2 door hardtop
jcc, I wouldn't worry too much about losing valuable volatiles (octane) by using a return line above fuel level. The gas cap prevents major loss, although, yes, the filler tube is vented.

Not sure returning fuel at fuel tank level is an issue, this is how stock return lines are situated in OEM sending units. And yes, returning liquid fuel into liquid fuel will ensure less loss of volatile components. I'm sure there is some pressure difference based on return line diameter, but whatever it is, it's not going to affect anything unless you're talking about a 400 hp or more engine that needs large diameter fuel/return lines and high volume flow. A slant six with 150-250 hp won't make a difference here or there, I'd surmise, as long as you have a good constant flow of fuel, say 20-30 gal/hr flow rate.

Brian

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 Post subject: Re: Return line?
PostPosted: Mon Jun 18, 2018 9:59 am 
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TBI Slant 6

Joined: Thu Jun 04, 2015 6:19 pm
Posts: 160
Location: Florida
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Little here I can dispute with your reply, but current OEM systems are effectively sealed and/or closed, so aromatics are restricted from out gassing, I think with our aftermarket solutions, that is not a normal option. Is it a big deal in the first place, no, for me however, I would still avoid it in my cars.


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 Post subject: Re: Return line?
PostPosted: Mon Jun 18, 2018 11:32 am 
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TBI Slant 6

Joined: Sat Nov 12, 2011 10:04 am
Posts: 193
Location: Upper So. CA
Car Model*: '65 Valiant 170 T5
All of the OEM EFI returns that I'm familiar with are part of the fuel pump & level sender assembly, and all that I've worked on or with install in the top of the tank. That just about insures that the returning fuel is introduced above the fuel level in the tank.

I don't doubt that a minimal restriction is going to make little difference, but a varying restriction induced change in fuel pressure seems like a bad idea when it is so easy to eliminate. This isn't an "Achilles Heel" kind of problem, this is a "Death of a 1000 Cuts" kind of problem.

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