Return lines with factory sending units
#1138994
12/18/11 09:32 PM
12/18/11 09:32 PM
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Toronto
mshred
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Hey guys, I am about to redo the fuel system on my car from the stock 5/16" line and mechanical pump. Plan is to go to a holley black pump with a sumped factory tank to feed my motor, and then have the same line teed off to feed my nitrous kit. For the nitrous regulator I plan on using a regular holley 2 port reg., and for the engine side I would like to run a return style regulator. My tank needs a new sending unit as mine is not working correctly anymore and after 3 repairs it is literally falling apart. I have seen some sending units on ebay, and some of them look to have a nipple to run a return line to My thoughts are to pick up a 5/16 sending unit with a return style nipple on it and use my factory 5/16 line as a the return line from the 3 port reg. to the return nipple at the tank...something along these lines I was thinking http://www.ebay.com/itm/63-76-Mopar-A-Bo...7#ht_2055wt_952Im also wondering if 5/16" return line is an appropriate size for returning fuel? especially if im running say a 3/8" or 1/2" feed line. Just not sure if the 5/16" has the capacity. Has anyone done this before? Just looking for some insight on this...thanks! 
Last edited by mshred; 12/18/11 09:37 PM.
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Re: Return lines with factory sending units
[Re: Challenger 1]
#1138997
12/19/11 01:09 AM
12/19/11 01:09 AM
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Toronto
mshred
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Quote:
5/16" is plenty big enough for a return.
that is good to know as I wasn't sure if it would be sufficient
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Re: Return lines with factory sending units
[Re: ahy]
#1138998
12/19/11 01:11 AM
12/19/11 01:11 AM
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mshred
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Quote:
The sending units with return niples use 1/4" return... even if the supply nipple is 1/2". Since you will get supply from the sump, you could use the main supply nipple on the sending unit as return... buy whatever size sending unit you want up to 1/2".
1/4" return is pretty restrictive and may make it hard or impossible to get fuel pressure where you want it for the carb depending on pump output. I used the 1/4" return nipple for a while with EFI and an A1000 pump. With that pump, the lowest pressure I could achieve was around 30 PSI... OK in my application since I was shooting for 45 but not so good for a carb.
Thank you for this info! I had no idea the nipples were a standard size, I thought they followed the size of the pickup. In that case, if I go with a 5/16" sending unit, I can run my 5/16" line back to it and it would already be in the right spot...But im just wondering how the fuel would like going through the sending unit backwards so to speak?
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Re: Return lines with factory sending units
[Re: mshred]
#1138999
12/19/11 01:47 AM
12/19/11 01:47 AM
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Joined: Jun 2003
Posts: 52,972
Romeo MI
MR_P_BODY
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Romeo MI
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Quote:
Quote:
The sending units with return niples use 1/4" return... even if the supply nipple is 1/2". Since you will get supply from the sump, you could use the main supply nipple on the sending unit as return... buy whatever size sending unit you want up to 1/2".
1/4" return is pretty restrictive and may make it hard or impossible to get fuel pressure where you want it for the carb depending on pump output. I used the 1/4" return nipple for a while with EFI and an A1000 pump. With that pump, the lowest pressure I could achieve was around 30 PSI... OK in my application since I was shooting for 45 but not so good for a carb.
Thank you for this info! I had no idea the nipples were a standard size, I thought they followed the size of the pickup. In that case, if I go with a 5/16" sending unit, I can run my 5/16" line back to it and it would already be in the right spot...But im just wondering how the fuel would like going through the sending unit backwards so to speak?
Since your putting a sump on it with the fuel outlet
being there then yes use the 5/16 for the return...
all you need to do is take the filter off the end
of the pick up tube... dont have the return near the
pick up(fuel to the pump) and you'll be fine... the
return size is really based on the pump your gonna
use... for instance if you use a 1000 PPH pump and
it doesnt have a return in the pump then your gonna
have to return all un-used fuel via that 5/16 and
still maintain steady fuel pressure... 5/16 wont
handle that kind of flow but with a smaller pump it
should handle it... also you need to look at each
bend in the line... every bend is restriction and
IF you have a bad(kinked) bend it wont handle it...
also remember that when we talk line/tubing we are
talking OD and on a 5/16 OD line its 1/4 ID so just
like the supply side, small can and will hurt you
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Re: Return lines with factory sending units
[Re: MR_P_BODY]
#1139000
12/19/11 01:57 AM
12/19/11 01:57 AM
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Joined: Apr 2009
Posts: 3,414
Toronto
mshred
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OP
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Posts: 3,414
Toronto
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Quote:
Quote:
Quote:
The sending units with return niples use 1/4" return... even if the supply nipple is 1/2". Since you will get supply from the sump, you could use the main supply nipple on the sending unit as return... buy whatever size sending unit you want up to 1/2".
1/4" return is pretty restrictive and may make it hard or impossible to get fuel pressure where you want it for the carb depending on pump output. I used the 1/4" return nipple for a while with EFI and an A1000 pump. With that pump, the lowest pressure I could achieve was around 30 PSI... OK in my application since I was shooting for 45 but not so good for a carb.
Thank you for this info! I had no idea the nipples were a standard size, I thought they followed the size of the pickup. In that case, if I go with a 5/16" sending unit, I can run my 5/16" line back to it and it would already be in the right spot...But im just wondering how the fuel would like going through the sending unit backwards so to speak?
Since your putting a sump on it with the fuel outlet
being there then yes use the 5/16 for the return...
all you need to do is take the filter off the end
of the pick up tube... dont have the return near the
pick up(fuel to the pump) and you'll be fine... the
return size is really based on the pump your gonna
use... for instance if you use a 1000 PPH pump and
it doesnt have a return in the pump then your gonna
have to return all un-used fuel via that 5/16 and
still maintain steady fuel pressure... 5/16 wont
handle that kind of flow but with a smaller pump it
should handle it... also you need to look at each
bend in the line... every bend is restriction and
IF you have a bad(kinked) bend it wont handle it...
also remember that when we talk line/tubing we are
talking OD and on a 5/16 OD line its 1/4 ID so just
like the supply side, small can and will hurt you
As usual Mr. P you bring up some darn good points!...If the 5/16" line is 1/4" ID then maybe it is too small to use. Like I said I was just planning on using the stock 5/16" line that is already there for the feed as my return once I sump the tank. Looks like the 5/16" really won't be enough though thinking about what your saying.
It would be nice to see if anyone else on here has used the stock 5/16" line as their return line after going to a larger feed and electric pump setup
Definitely some more food for thought, thanks
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