Quick fuel line question
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Quick fuel line question

  1. #1
    Senior Member N2GLOCK's Avatar
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    Default Quick fuel line question

    What sized diameter fuel line is adequate for a mild BBC (400 HPish)? I'm talking about the fuel lines between the tanks and the water seperator head. I currently have 3/8" and the engine ran a little on the lean side last year. Should I upgrade the lines and the head to 1/2" or am I safe with the current 3/8"? Thanks
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    Senior Member SuperJet's Avatar
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    Quote Originally Posted by N2GLOCK View Post
    What sized diameter fuel line is adequate for a mild BBC (400 HPish)? I'm talking about the fuel lines between the tanks and the water seperator head. I currently have 3/8" and the engine ran a little on the lean side last year. Should I upgrade the lines and the head to 1/2" or am I safe with the current 3/8"? Thanks
    You should be fine with 3/8". What size are the bungs on your tank? I they are only -6 or 3/8 barb then it really is pointless to go up to 1/2" unless you up the size of your pickup tubes also.


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    Some guy obnoxious001's Avatar
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    Quote Originally Posted by N2GLOCK View Post
    What sized diameter fuel line is adequate for a mild BBC (400 HPish)? I'm talking about the fuel lines between the tanks and the water seperator head. I currently have 3/8" and the engine ran a little on the lean side last year. Should I upgrade the lines and the head to 1/2" or am I safe with the current 3/8"? Thanks
    I am pretty sure you are good with 3/8", and some other issue was causing your "lean" condition. Could have been fuel filter or some other obstruction, maybe a pump problem,, or perhaps the tune up, carb jetting and/or timing.

    I have run a large cubic inch, twin 850 cfm carb engine on the dyno with a -6 (3/8") feed without starving the engine for fuel as evidenced by the results. It was set up with -8 from the fuel pump, but a leaking fitting caused us to substitute a -6 tee to the carbs. It did get changed back to -8 once it left the dyno, but apparently -6 supported 750 HP without dropping fuel pressure or volume.

    That being said, I build small block race engines for a dirt modified, and I had him put a -8 supply line from the tank, partially so the volume of the fuel line might be helpful. Not quite the same as the Nascar guys using larger fuel lines to increase their fuel capacity beyond the mandated fuel cell size.
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    read this article. its pretty informative. flow rates, even goes down to the fittings themselves. stay away from 90* bends, etc. its a little biased towards cars but just replace "axles and jacking plates" with "stringers and transoms" heh.

    How To Build The Proper Fuel System For Carbureted Motors - Chevy High Performance Magazine

    how much more is there to a carb fuel system other than "just keeping the bowls filled"?
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    Senior Member N2GLOCK's Avatar
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    Thanks for the replies so far. What got me wondering about this is me and my dumb ideas. I've always wanted to run a water seperator filter that has a built in drain on the bottom side. My water seperator head has 3/8" NPT ports on the side and only acccepts filters with 11/16"-16 threads and none of those filters are available with a drain. The filters with drains on the bottom have either 3/4" or 1" threads and if I wanted to run any of those I would need to buy a water seperator head with 1/2" NPT ports. So far my plan is to buy the water seperator head with 1/2" NPT ports so I can run a filter with drain and then run 3/8" line from the tanks in case I can't change the bungs on the tanks themselves. There isn't alot of room between the gunnel and the tops of the tanks so changing the bungs may not be possible.
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    Quote Originally Posted by N2GLOCK View Post
    Thanks for the replies so far. What got me wondering about this is me and my dumb ideas. I've always wanted to run a water seperator filter that has a built in drain on the bottom side. My water seperator head has 3/8" NPT ports on the side and only acccepts filters with 11/16"-16 threads and none of those filters are available with a drain. The filters with drains on the bottom have either 3/4" or 1" threads and if I wanted to run any of those I would need to buy a water seperator head with 1/2" NPT ports. So far my plan is to buy the water seperator head with 1/2" NPT ports so I can run a filter with drain and then run 3/8" line from the tanks in case I can't change the bungs on the tanks themselves. There isn't alot of room between the gunnel and the tops of the tanks so changing the bungs may not be possible.
    my tanks have pickup tubes attached (welded) to the fittings that go into the bungs. when i tried to "update" the fittings cuz they were ugly compared to all this nice AN stuff i bought, i couldnt get em out cuz of the tube inside and gunnel clearance. my water seperator (standard west marine issue, $40) has 1/2" NPT, but no drain. where exactly would u drain it to? the bilge might be a bad idea cuz there would be traces of fuel still in the water, and dumping it overboard makes the fishes sad. im 8- from the carb to the tanks, then it goes down to 3/8" at those stupid fittings. :grr:
    Last edited by ka0tyk; 03-23-2012 at 11:35 PM.
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    Senior Member SuperJet's Avatar
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    All tanks with a fitting at the top will have a pick up tube


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    Quote Originally Posted by ka0tyk View Post
    my tanks have pickup tubes attached (welded) to the fittings that go into the bungs. when i tried to "update" the fittings cuz they were ugly compared to all this nice AN stuff i bought, i couldnt get em out cuz of the tube inside and gunnel clearance. my water seperator (standard west marine issue, $40) has 1/2" NPT, but no drain. where exactly would u drain it to? the bilge might be a bad idea cuz there would be traces of fuel still in the water, and dumping it overboard makes the fishes sad. im 8- from the carb to the tanks, then it goes down to 3/8" at those stupid fittings. :grr:
    All CG approved tanks installed by the manufacturer are required to have a anti siphon valve at the fuel pickup. It will be the biggest restriction in a 3/8 fuel system. They are usually constructed of aluminum and look like a normal hose bung only a little longer. I think Imco has high performance valves but they may not be 3/8.
    Last edited by tigertooth; 03-24-2012 at 05:18 AM.
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    Quote Originally Posted by ka0tyk View Post
    my tanks have pickup tubes attached (welded) to the fittings that go into the bungs. when i tried to "update" the fittings cuz they were ugly compared to all this nice AN stuff i bought, i couldnt get em out cuz of the tube inside and gunnel clearance. my water seperator (standard west marine issue, $40) has 1/2" NPT, but no drain. where exactly would u drain it to? the bilge might be a bad idea cuz there would be traces of fuel still in the water, and dumping it overboard makes the fishes sad. im 8- from the carb to the tanks, then it goes down to 3/8" at those stupid fittings. :grr:
    Draining the water out of the filter directly into the bilge or overboard is definitely not an option. I think the purpose of the drain is to remove water from the filter between changes. I was thinking of running the Wix filter Standard High Volume Filter/Separator, 7-1/2" Tall - CP Performance If I was a real baller I'd run the Canton Racing unit that uses a replaceable cartridge filter inside the anodized blue canister https://www.cantonracingproducts.com...ion&key=25-922
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    The longer a fuel line is, the more resistance it will have. The fitting size shouldn;t necessarily dictate the size of the fuel line. Even for a 3/8 fitting or pick-up, if your fuel line is more than about 4' long, I'd up the size to 1/2" or -8. Also remember that if you're drawing out of both thanks at the same time you need to have equal length fuel lines from each, or you'll empty one before the other.
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