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Thread: fuel line help

  1. #1
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    fuel line help

    Hey all,

    (apologies in advance for another fuel line routing thread)

    I have an MKIV complete kit - planning on a 302 based carb engine with power steering.

    Up to this point in the build I have managed as a new builder w/o the benefit of built school to manage mostly on my own (of course with the help of the videos and the voluminous knowledge on the various forums). But at this point I'm out of my league a little in that I have never run any sort of fuel/power steering/brake lines. Please forgive me if my questions are overly basic.

    I think I understand with a carburetor that the fuel line should optimally come up into the engine compartment on the driver side. That means that at some point I'll need to route the lines from the passenger side to the driver side at some point.

    I've also gathered that there are numerous options on the type of lines and diameters of lines that can be used. I guess I'm overwhelmed by the options at this point.

    So I'll start with this basic question and ask more about the types of lines later on:
    Where, on a MKIV (3 link solid axle rear end - if that matters) is the right place to cut over to the driver side? I may be reading pictures from other posts incorrectly, but I've seen it come across the upper cross member of the frame, sort of behind the seat back area (again, I think I've seen one where EdwardB did that) but in the pics I've seen that cross member is relatively empty of obstacles. Mine looks like this: (picture taken facing the front of the car from right above the rear end gear box but under the triangular metal plate)

    20190416_195822.jpg

    I'm trying to avoid running the lines where aluminum, a battery, or something else will end up being.

    If the answer is to drill and mock up the rear and trunk area I'm ok with that. Just trying to figure out a first step in knowing what to do here.

  2. #2
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    I have the same setup, are you using an electric or mechanical fuel pump? I chose mechanical and was recommended to increase fuel line size to 3/8. I’d suggest getting NiCop lines as they are much easier to bend.
    If you are using an electric pump you will most likely have to also run a fuel return line.
    Mine goes from under the trunk floor, down to the outside of the drivers side 4” frame tube, forward to just behind the front suspension. I have a rubber hose from the hard line under the trunk down to the fuel tank and a braided 6an line from the front end of the fuel one to the mechanical pump on the engine.
    If you haven’t yet I’d run brake lines at the same time, so you don’t find them interfering later.

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    Just noticed you said battery. Have you decided where to put it? I’d suggest the breeze front mount.

  4. #4
    Senior Member edwardb's Avatar
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    I'm assuming for your carb'd setup you're also planning a mechanical engine driven pump? If so, then yes, a single line is all you need and it should terminate on the LH side, approx per the picture below. On my #7750 build, also carb'd with mechanical pump, went from the tank, across the back of the chassis tube under the trunk in front of the tank, over to the large vertical tube that goes down to the end of the 4-inch round tube, then to the front along the outside of the 4-inch tube. Placed as high as possible. Of course check to make sure, but none of these locations or routing should interfere with chassis aluminum or wiring. I ran the front to back brake line next to the fuel line on the outside of the LH 4-inch round tube as well.

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    Thanks all!

    Yep, a mechanical fuel pump - but based on that:
    Does that mean that I should remove the filter that was included in the kit? I did install it already, but removing it would be easy.
    If I switch out to 3/8" line, do need to invest in and install new fuel pick-up for the tank? I did drill the end of the send-line to open it up a bit as the manual suggested.

    I'll check out that breeze battery mount today. My initial thoughts were to just put the battery where it suggests in the manual (the trunk). I'm new to the whole build-a-car thing so I'm defaulting to going by the book as my typical route, but if you have a better suggestion I'm all for it.
    Last edited by welske; 04-17-2019 at 07:54 AM.

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    Senior Member cv2065's Avatar
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    I'm using an in-tank electric pump with 3/8" NiCop lines. Very easy to bend, even at that size. I wasn't able to run a mechanical pump due to my PS setup, so had to run a return line as well for my in-tank electric. Good news is that I'm setup for FI if I ever decide to go that direction. I chose to run up the passenger side as I thought two 3/8" lines with the brake line was a little congested for one side, but I don't think there are any wrong choices...just preference. My hard lines stop about a foot or less before my regulator or fuel filter, then continue on with 6AN braided lines.
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  7. #7
    Not a waxer Jeff Kleiner's Avatar
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    Quote Originally Posted by welske View Post

    Yep, a mechanical fuel pump - but based on that:
    Does that mean that I should remove the filter that was included in the kit?
    The filter needs to be on the pressure side of the pump, not the suction side.

    RE: Battery location; unless space limitations dictate otherwise I prefer the front location for a few different reasons; shorter cables, increased trunk room, better weight distribution.

    Good luck!

    Jeff

  8. #8
    Senior Member skidd's Avatar
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    Quote Originally Posted by cv2065 View Post
    I'm using an in-tank electric pump with 3/8" NiCop lines. Very easy to bend, even at that size. I wasn't able to run a mechanical pump due to my PS setup, so had to run a return line as well for my in-tank electric. Good news is that I'm setup for FI if I ever decide to go that direction. I chose to run up the passenger side as I thought two 3/8" lines with the brake line was a little congested for one side, but I don't think there are any wrong choices...just preference. My hard lines stop about a foot or less before my regulator or fuel filter, then continue on with 6AN braided lines.
    I did something similar to you.
    I realize the OP is going mechanical fuel pump.. but.. a little food for thought for you...

    I ran my fuel lines all up the passenger side, and the rear brake line down the drivers side.

    I have an in-tank low-pressure electric fuel pump. It perfectly fit into the stock mustang fuel pump hanger. (Spectra SP1138 $30 & Spectra STR01 Strainer $5). Makes 5(ish) psi dead-headed at my carb.
    Also, an OEM inline fuel filter back at the tank end of the lines.
    Like CV, I ran both a feed, and return line from the tank all the way up the passenger side. Stopping just about 3/4 of the way up the passenger foot-box wall.
    My return line is just blocked off in the engine compartment. Lastly, A piece of fuel hose runs from the feed line, dead-headed to the carb inlet port.
    All run with the fuel lines provided in the kit. Now I'm also setup for FI in the future if I ever want to switch.
    The 5/16 line in the kit is more than enough for a mild/medium 302, with electric in-tank pump.
    It's far easier for an electric pump to push against a 5/16 line.
    If you do stay with a mechanical pump, it might in fact be a good idea to upgrade to 3/8 line. Less restriction on the suction side. But, I'm only guessing here.
    There are plenty of old-school muscle cars that came stock with a mechanical pump, and 5/16 fuel line.

    Not trying to convince you to go with an electric pump. Just making sure you know that it can be really easy to to, and not expensive for a carb... and even without a low pressure return regulator.
    I'm a big fan of electric fuel pump systems because they do an excellent job when it comes to pushing fuel. And.. will vastly reduce the chances of getting any vapor lock near the carb on those hot summer days.

    The blue painters tape is temporarily holding the 2 lines in place. I fabricated a simple aluminum block to hold them both solidly on the side of the foot box.


    The pump and strainer held in the factory hanger with a stainless hose clamp.
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  9. #9
    Senior Member Avalanche325's Avatar
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    The stock 5/16" line is good to about 400hp. If you are over that, bump it up to 3/8". You will need a decent flare tool for 3/8" steel. Those cheepie $30 ones tend to slip. Ridged makes one that works well without breaking the bank.

    I don't often disagree with Jeff, but leave the battery in the back. These cars need the weight in the rear. That is why they are a front mid engine layout. The FFMetals under floor trunk box preserves your trunk space and moves the weight lower. I do recommend going up a size on the cables.

  10. #10
    Senior Member CraigS's Avatar
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    I know it is always recommended to put the fuel filter on the pressure side but mine has been back near the tank for 10 years w/o any problem. This is the replacement element it uses.
    https://www.summitracing.com/parts/pfs-10120
    If you compare the specs to the one FFR supplied that might help w/ deciding whether to use it or not. I don't think it makes any difference which side you run the line on. It comes out of the tank on the right and has to end up on the left. Doing the crossing in the front or back functionally makes no difference. I also like the NiCop line but FFR already sent you line, and you are going w/ a 302, so their line will be fine.
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    You guys are a big help! One thing I really like about this whole endeavor is how it is such a personal build where everyone can do it how they think best. So I really appreciate the help and the different advice!

    After talking to the engine supplier, Blueprint, about the engine package I'm planning on using, I was "educated" that it includes a Holley Red electronic return-less fuel pump. So I accidentally lied to the thread above when I said mechanical - sorry about that - luckily I got great advice for electric and mechanical so it worked out.

    Blueprint says for this engine package (347 w/TKO600) I can mount the fuel pump on the passenger rear oval tube and just bring the line down the passenger side from the tank. So I think the picture is getting clearer - I plan to use 3/8" lines, all passenger side, have the fuel pump connected to the stock FF tank intake, and then a the fuel filter in between the pump and the carb at some point.

    I guess I do have one question in general about fuel lines (and other type lines in general). If you decide on a certain diameter (like 3/8"), in order for that line to provide the associated liquid for that diameter, does that mean that at NO POINT in the path can you restrict the line to less than the diameter you are shooting for (in this example, 3/8")?

    I wonder that because I'm not sure if the FF stock fuel tank intake unit and the FF stock fuel filter valves are 3/8" and if they would function as "pinch points" to the fuel, making the 3/8" line ineffective. I'm guessing in this case it won't be an issue either way, but for future reference in other applications...

  12. #12
    Senior Member edwardb's Avatar
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    Ideally, yes, all the fittings, fuel tank pickup, etc. should not be any smaller than the fuel line used.
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    Senior Member phileas_fogg's Avatar
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    Like edwardb says, no restrictions less than 3/8". The stock fuel pump hanger is 5/16" (with a 1/4" return), as is the F5-provided fuel filter & fuel pickup (at least that was the case on my kit, delivered nearly 4 years ago).


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    Senior Member Avalanche325's Avatar
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    Quote Originally Posted by welske View Post
    So I accidentally lied to the thread above when I said mechanical ...
    That's it! You're out of the club!

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    Dang - I need this club. No one else will let me into theirs.

    I guess that means I need to pick up a filter and another fuel pickup. As far as the lines, it sounds like 3/8" NiCop keeps popping up so I'll check that out. Thanks again all!

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    Maybe one more question - when other people upgraded to 3/8" lines, did they replace the fuel pickup? If so, with what? In this case the Holley Red electrical pump is not an in-tank pump so I think all I need is a basic pickup with 3/8" pipe, but I'm not having luck finding such a thing online.

  17. #17
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    I’m using 3/8 lines and 5/16 pickup. No issues. Can’t remember all the science on it but when I did my research on this, it wasn’t necessary that all fittings were 3/8. Larger line is something to do with speed of travel and it’s more critical to have the larger diameter on the long runs.
    Think of the tiny holes the fuel finally passes through in the carb.

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    Thanks Murd. Good point on the carb. Again - all you guys out there are really, really helpful.

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    https://www.breezeautomotive.com/sho...e-barb-outlet/

    Most if not all fittings sized for say 5/16" hard line will have a minimum ID that is less than the ID of the steel hard line.
    Same for 3/8" OD hard line. The majority of the pressure drops occur at the fittings, elbows in particular, rather than the straight runs of tubing. Smooth bends in tubing are basically the same as straight and don't cause a pressure drop.
    A 347 stroker probably be fed with 3/8" line and fittings which are more common and available anyway. Since it is low pressure you only need fittings at the pump inlet and outlet. Everything else can be just hose barb.
    My 1967 Mustang with a 289 2 barrel came with 5/16" line.
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  20. #20
    Senior Member CraigS's Avatar
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    Ideally the pickup should be 3/8 but, IMHO I wouldn't worry about it. If you were going to be road racing the car, maybe it could be a problem because of the long runs at full throttle. In any kind of normal driving, even in autocrossing, I am sure the pump will be able to keep up w/ the fuel requirements.
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  21. #21
    Senior Member edwardb's Avatar
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    Quote Originally Posted by Murd View Post
    ...Think of the tiny holes the fuel finally passes through in the carb.
    Quote Originally Posted by welske View Post
    Thanks Murd. Good point on the carb...
    A technicality I guess, but the carb circuits and jets are fed from the supply in the fuel bowls. The job of the fuel pump, lines, fittings, etc. is to keep the bowls full. Needs to have the capacity to do so.
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    Quote Originally Posted by edwardb View Post
    A technicality I guess, but the carb circuits and jets are fed from the supply in the fuel bowls. The job of the fuel pump, lines, fittings, etc. is to keep the bowls full. Needs to have the capacity to do so.
    I’m going to say I’m far from an expert on the subject, however the real choke point is what feeds the float bowls, the needle valves/seats, which are tiny compared to a 3/8 line. It works because the fuel only has to flow through those valves for a very short distance, so it can speed up and get through without a lot of friction. If you tried to run the fuel through lines that small for any distance there would be far too much friction/pressure built.

    My only point is to have a smaller fuel line for a short distance, like 1’ of 5/16 fuel pick up in a 10’ 3/8” fuel line, does not choke the system down to the same as a 5/16” system. The friction and pressure increases with the length of the line so you use a bigger diameter line in order to slow the fuel down and reduce the friction and pressure. Apparently this is even more important in a mechanical fuel pump setup as most of the system is under vacuum, not pressure, so bigger lines are more important with a mechanical pump.

    I don’t know enough to comment with confidence on whether a 5/16 pickup is ok for this specific setup, but from my own research I would feel it is.

  23. #23
    Senior Member edwardb's Avatar
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    Quote Originally Posted by Murd View Post
    I’m going to say I’m far from an expert on the subject, however the real choke point is what feeds the float bowls, the needle valves/seats, which are tiny compared to a 3/8 line. It works because the fuel only has to flow through those valves for a very short distance, so it can speed up and get through without a lot of friction. If you tried to run the fuel through lines that small for any distance there would be far too much friction/pressure built.

    My only point is to have a smaller fuel line for a short distance, like 1’ of 5/16 fuel pick up in a 10’ 3/8” fuel line, does not choke the system down to the same as a 5/16” system. The friction and pressure increases with the length of the line so you use a bigger diameter line in order to slow the fuel down and reduce the friction and pressure. Apparently this is even more important in a mechanical fuel pump setup as most of the system is under vacuum, not pressure, so bigger lines are more important with a mechanical pump.

    I don’t know enough to comment with confidence on whether a 5/16 pickup is ok for this specific setup, but from my own research I would feel it is.
    All good points. Nothing to disagree with here. Not from me anyway... My first thought when you said tiny holes in the carb was to the jets and such. But you're right. The needle valve/seats associated with the carb floats and bowls are small too. There needs to be adequate pressure and flow at that point to keep the bowls full. At the end of the day, the OP's original question about his 302 based carb engine, assuming it's not anything crazy, is probably OK with 3/8 lines and 5/16 fittings. That would be a very safe installation. Fact is it would probably be OK with 5/16 lines and fittings if a mild 302 and is going to see mainly street driving. I stick with my earlier response that all 3/8 including fittings is "ideal" but in this case likely doesn't warrant throwing a bunch of stuff away.
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  24. #24
    Senior Member Avalanche325's Avatar
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    I modified my fuel pickup. It is really 3/8" tubing but pinches down on both ends. I cut the restricted ends off. I brazed a fitting on to go to 3/8 hard line. Not a fun task, but I got it done.

    It doesn't really matter what size the engine is. It matters how much HP you have to feed. For instance a 347 can have 340hp. That will use much less fuel than a 347 with 500hp.

    I have a filter in the "stock" location. However, it is a low restriction Fram Racing cartridge filter. I also have a filter just before the carb. Mechanical pump, then a regulator.

    Craig is probably right. You won't be at WOT long enough to really matter.

  25. #25

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    Another note: A diaphragm pump pulsates between max flow and no flow. (half the time there is no flow as the pump takes the next gulp) This is different from an EFI gerotor pump that is continuous flow. So for the same flow rate the diaphragm pump wants a larger minimum flow area to achieve the same flow rate at a given same maximum velocity.
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