fuel tank question

[Ta2edjr]

Using my factory in cab fuel tank for now...while plumbing up a return line I was wondering something...so here it goes how far down in the tank should the return line go? Right now my return line stops about 6 inches from the top of the tank. Should it go to the bottom of the tank like the supply ?

[Aruba1]

I am not sure but since it's a return line I don't think it matters as long as it goes back to the tank? Anyone else? At least in my case I just hooked the return hose from the corvette fuel filter back to the tank and wished it well. I am running stock in-cab tank also.

[Ta2edjr]

Originally Posted by Aruba1

I am not sure but since it's a return line I don't think it matters as long as it goes back to the tank? Anyone else? At least in my case I just hooked the return hose from the corvette fuel filter back to the tank and wished it well. I am running stock in-cab tank also.

Aruba thanks for the info! I won't sweat it I'll keep on truckin on this build. By chance you wouldn't know how much pressure the return line has on it? Maybe a few pounds if any is what i had in mind but never hurts to ask

[Heavymetl]

Fuel return needs to go near the bottom of the tank. You don't want a fuel spray from the top. Leads to aeration, heat, cavitation....all sorts of issues easily avoided.

[LockDoc]

Originally Posted by Ta2edjr

Aruba thanks for the info! I won't sweat it I'll keep on truckin on this build. By chance you wouldn't know how much pressure the return line has on it? Maybe a few pounds if any is what i had in mind but never hurts to ask

I don't see how it can have any pressure on it when it is going into an open vessel (fuel tank) that is actually having a vacuum drawn on it by the fuel pump.

LockDoc

[slotard]

Originally Posted by Ta2edjr

Aruba thanks for the info! I won't sweat it I'll keep on truckin on this build. By chance you wouldn't know how much pressure the return line has on it? Maybe a few pounds if any is what i had in mind but never hurts to ask

There will be minimal pressure, higher at the rail and decreasing as it gets closer to the tank. The hose has some resistance.

Originally Posted by Aruba1

I don't know, people run into a lot of theoretical problems that may or not may be a problem in the real world. Some manufacturer actually recommend the return line on top of the tank, others suggest brazing a bung in the neck. I know that using the return bung on the stock tank works fine for me. But my truck is build for towing, probably if will have a different effect if I was going after speed, crazy HP, boost, etc? If I ever run into any issues I will post it on here.

I just wonder how many times their fuel being pushed back in the tank? Does it do it when slowing down or letting the throttle go? I personally would rather have it spraying on the top then from the button and pushing bubbles in the gas. Sorry, I am just thinking out loud.

The return line doesn't have any bubbles in it unless your fuel line did, having it at the top makes it more likely to get bubbles thanks to splashing.

It'll flow most when you let off.

[LockDoc]

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If the return line needs to be below the fuel surface at all times it would have to be near the bottom of the tank. I am not an engineer or even very smart, but common sense tells me that if you put a pressure gauge on a return line that is flowing freely it is not going to show any pressure. If the return line is below the surface of the fuel it may show a slight amount, and the further down in the fuel it is the more pressure it will show but still not much.... Dunno....


While we are on the subject of fuel return I see no reason that the return line couldn't be fed back into the fuel pump inlet with a tee or wye fitting. (I think a wye would be better for the flow) I was going to try this on my '67 Panel Truck but I had to buy a new fuel tank and it had a return line fitting on it. Has anyone tried this????

LockDoc

[Heavymetl]

Originally Posted by LockDoc

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If the return line needs to be below the fuel surface at all times it would have to be near the bottom of the tank. I am not an engineer or even very smart, but common sense tells me that if you put a pressure gauge on a return line that is flowing freely it is not going to show any pressure. If the return line is below the surface of the fuel it may show a slight amount, and the further down in the fuel it is the more pressure it will show but still not much.... Dunno....


While we are on the subject of fuel return I see no reason that the return line couldn't be fed back into the fuel pump inlet with a tee or wye fitting. (I think a wye would be better for the flow) I was going to try this on my '67 Panel Truck but I had to buy a new fuel tank and it had a return line fitting on it. Has anyone tried this????


LockDoc

Too much heat introduced by recirculating the same fuel. No way I'd do a setup like that. In tank pump with correct return plumbing is the way to go for a N/a LS.

[Aruba1]

Sorry I don't. I just used an Autozone FI hose, I believe they are good for 50-65 PSI, more than the return line will ever see ;-). I wouldn't advice to use anything with less pressure than that. And if you can get higher rated lines for the whole system would be even better.

[Aruba1]

I don't know, people run into a lot of theoretical problems that may or not may be a problem in the real world. Some manufacturer actually recommend the return line on top of the tank, others suggest brazing a bung in the neck. I know that using the return bung on the stock tank works fine for me. But my truck is build for towing, probably if will have a different effect if I was going after speed, crazy HP, boost, etc? If I ever run into any issues I will post it on here.

I just wonder how many times their fuel being pushed back in the tank? Does it do it when slowing down or letting the throttle go? I personally would rather have it spraying on the top then from the button and pushing bubbles in the gas. Sorry, I am just thinking out loud.

[Heavymetl]

Must watch video about EFI fuel return.

http://youtu.be/dP6Pogm6Ts0

I've seen plenty of "real world" fuel delivery issues on Power Tour and Drag Week. Take the time to do it right!

[Aruba1]

After watching the video I am even more confused. Does anyone know how much pressure is in the return line and when does this pressure kick in? Based on the video it sounds like there is constant flow and it doesn't make sense. There should be some pressure (1 or 2 PSI at the most?) but not a lot and definitely not constant. Or can the return line see as much pressure as the pump can put in some unique situations?

[ls1nova71]

Originally Posted by Aruba1

After watching the video I am even more confused. Does anyone know how much pressure is in the return line and when does this pressure kick in? Based on the video it sounds like there is constant flow and it doesn't make sense. There should be some pressure (1 or 2 PSI at the most?) but not a lot and definitely not constant. Or can the return line see as much pressure as the pump can put in some unique situations?

When youre going down the road and let completely off the gas, the injectors are not using nearly as much fuel, and with the pump running constantly, the extra fuel has to go somewhere, that's what a return is for. There will be a considerable ammout of fuel returned to the tank during normal driving.

[Aruba1]

Here are some info on EFI return line but on Mustangs... http://forums.vintage-mustang.com/mo...turn-line.html

[BR3W CITY]

The amount of fuel in the return line is a function of the pump. A pump that can oversupply the rail OR an extremely low injector cycle will bypass more fuel.

Think of it like a drinking fountain. It pumps the same amount of water, and the drain only gets what you don't use. If you start taking bigger gulps, less ends up in the drain. If you pump more water, but use the same amount, more ends up in the drain.

If your truck is running DFCO, it will also change the amount of fuel being returned because the ECM will be demanding fuel at times even though your TPS % is low.