Fuel system question

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I'm getting ready to install my fuel tank and will have to figure out how I'm going to run the fuel lines.
I am running EFI, my new tank is a modified stock tank by Rock Valley, with an in-tank pump.
The top of the tank has what appear to be 3/8" female fittings for vent, feed, and return.

I picked up some 1/2" aluminum line that I was planning on running for the return. (I had always read that the return line should be larger to prevent any pressure in the line which could throw off the regulator. I've seen that some people here disagree with that.)

My current plan is to make a bracket near the tank that the lines from the engine compartment will mount to, and then the flex lines from the tank will mount to the fittings on the bracket.
The bracket will probably hold the fuel filter as well.

Has anyone got any feedback, suggestions or recommendations?

TIA! :cheers:

[Hammered]

For that pump, 3/8" should be plenty. Al may not be a good line material choice on the street though. Btw, I posted a bunch of EFI sizing info that I've collected here: http://john.my67.net/efi.htm The pump you have is 255 l/hr.

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I would not plan on running aluminum for the pressure line, but I was thinking that it might be okay as a return line. Am I wrong?

[Hammered]

The problem with thin wall aluminum tubing is that it is prone to fatique cracking. It also burns through easy potentially turning a small fire into a big one.

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Okay then. I briefly thought about perhaps using it for the vent line, but I guess the fire thing is still going to be an issue.
Looks like there really isn't a place for this tubing on a street car, is there?

[Fuelie Fan]

I'm not sure I would get too worked up about a fire hazard, personally. Look beneath your newer cars; their fuel lines are plastic. Good planning can also prevent most fatigue concerns, but if you've never bent aluminum before you may want to learn on something other than your fuel system.

[parsonsj]

The aluminum tubing will be fine. Just be aware that it needs to be bent and secured correctly. It will fatigue more quickly than stainless steel, a lot more quickly than mild steel, and way way more quickly than plastic. Even with that, it will likely outlast the car before fatigue becomes a concern.

jp

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Hammered, I've got a couple more questions for you:

I see that your charts have supply by HP and return by volume, and I was wondering how the HP rating determines supply size, and why the return size doesn't need to follow.
I understand that you don't want to restrict the flow feeding the engine, so you need larger line to supply the power, and that the pump determines what volume of fuel can be pumped, so return must allow for that volume, but why is the return smaller than the feed?

Also, what kind of line should be used? I have some -8 braided line, but I've heard some people don't like it for fuel. It seems they like Teflon lines, but you have to replace them periodically, IIRC.
I plan on running hard line for most of the run, but I will need flexible line at the junctions from the body to the engine and the tank.

TIA!

[Hammered]

First, the info on my site was collected from various sources so I can't go into how these guidelines were arrived at. Second, I don't believe there is anything that says the return should be smaller than the supply although I wouldn't see the sense of having it larger than the supply. The order of sizing goes like this: knowledge of engine HP & BSFC X factor of safety determines max required fuel flow. This determines the pump size which determines the return line diameter. The supply is also based on max required fuel flow.

Line resistance is of most concern when the engine load requirements demand full flow. At this same condition, the lowest percentage of supplied fuel is being returned to the tank. Therefore, a supply larger than the return makes sense but is not a must.

Hope this makes sense to you.

I used braided hoses with teflon liners, but that is overkill. Hardline is nice, but 1/2" SS is near impossible to work with hand benders. If you want quick, easy and nice, you might go with the teflon lines.

[Z-man]

I understand that you don't want to restrict the flow feeding the engine, so you need larger line to supply the power, and that the pump determines what volume of fuel can be pumped, so return must allow for that volume, but why is the return smaller than the feed?



The return doesn't have to be as big because 1) it's at atmospheric pressure (low) and there isn't the resistance of a regulator in that section of tubing so the fuel flows easily and 2) hopefully, you're burning a portion of the fuel so there's not as much to return to the tank... :)

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The return doesn't have to be as big because 1) it's at atmospheric pressure (low) and there isn't the resistance of a regulator in that section of tubing so the fuel flows easily and 2) hopefully, you're burning a portion of the fuel so there's not as much to return to the tank... :)
That part I understand. ;)
The part I wondered about was more for at idle, where a majority of the fuel is being bypassed, and if any pressure builds up in the lines it could raise the fuel pressure. I don't think it'd hurt anything, but I could see it causing some problems with tuning the engine.

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I used braided hoses with teflon liners, but that is overkill. Hardline is nice, but 1/2" SS is near impossible to work with hand benders. If you want quick, easy and nice, you might go with the teflon lines.
Did you run the hose for the whole run? I don't think that passes tech at most tracks, and that's my main concern. (Or did I misunderstand you?)

My plan was to run hard line basically from the engine compartment to the rear end, and then use braided to connect the tank and the engine to the hard line.
From what I have read, if I go with stainless tubing it will be easiest to buy prebent. If I go with regular steel I'll make them myself.

[Hammered]

That part I understand. ;)
The part I wondered about was more for at idle, where a majority of the fuel is being bypassed, and if any pressure builds up in the lines it could raise the fuel pressure. I don't think it'd hurt anything, but I could see it causing some problems with tuning the engine.

If you are worried about back pressure in the return line affecting the regulator's performance, I wouldn't. As long as the tank is vented well, the regulator won't see a highly varying return pressure which will affect the regulator more than a steady back pressure would. As Z-man said, the regulator sees atmospheric + line pressure drop on the return side. This pressure should be substantially lower than the supply side pressure, even if the line size is one step smaller.

I ran SS line the whole length with braided, teflon lined hose for short distanances where flexing was required. I don't know what track rules you'll be under, but I've seen race cars with full length flexible hose run. I'm not saying it legal or wise, I'm just saying that I've seen it.

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Okay, that's what I thought you did. We are on the same page.
I guess I just need to see if one of the companies out there can modify their stock product to meet my plan without raising the cost too much.

[Hammered]

www.Rightstuffdetailing.com did upsized lines for me. I think the supply and return cost an extra $100 to $140 over the regular price.

If you can get away with 3/8", do it. 1/2" is a major PITA.