no return fuel system

fordf550 · Apr 24, 2012

im working on a new fuel system for the 7.3 among various other upgrades. im using a airdog 150 adjusted to 65 psi. not planning on returning any fuel other than what the airdog does. running 1/2 line up to a injector feed lines that are -6 jic. 1/8 inch npt to -6 adapters in heads, feeding fuel from all four corners. im expecting a pressure drop of no more than 10 psi at wot. 50 psi low pressure indicator on line at heads. hope she flows well. any thoughts?

old man dave · Apr 25, 2012

how do you propose dealing with trapped air like after any fuel system work? One of the reasons the SD guys install a regulated return is to be able to purge air out of the system without pushing the air out through the injectors. Another is to push fresh cool fuel through the engine at low fuel demand occasions, without a regulated return the excess fuel would just heat up in the head. I also like the idea of regulating fuel pressure at the end of the fuel flow path instead of regulating supply side pressure. I see a maximum pressure drop of less than 2psi with my single pump Bean's system using the supplied AN-6 lines. I expect my next fuel system, a fuelab/AN-10 lines with a regulated return, to have no pressure drop feeding B codes.

907DAVE · Apr 25, 2012

old man dave said:
how do you propose dealing with trapped air like after any fuel system work? One of the reasons the SD guys install a regulated return is to be able to purge air out of the system without pushing the air out through the injectors. Another is to push fresh cool fuel through the engine at low fuel demand occasions, without a regulated return the excess fuel would just heat up in the head. I also like the idea of regulating fuel pressure at the end of the fuel flow path.

Both those idea's have a very convincing argument why they are NOT true or beneficial.

Anyone know why?

PsRumors · Apr 25, 2012

907DAVE said:
Both those idea's have a very convincing argument why they are NOT true or beneficial.

Anyone know why?

Why don't you tell us?

907DAVE · Apr 25, 2012

LOL

First off, lets think about about getting air into the fuel system, how does it get there?

Either you disconnect something, pull injectors, run out of fuel or.......... you have a air leak or something in the system creating cavitation.

If you are getting air into the fuel system during normal operation then 100% of that air is being passed through the heads and the chances of that air getting forced through the injectors is much greater than if you were to draw just enough fuel as the engine needs.

As for the "cool fuel" idea...anyone with a regulated return ever feel there fuel tank after a few hours of operation?

That sucker gets pretty warm. This type of fuel system is actually turning your engine into a fuel heater. If you return fuel before it even hits the heads the fuel remains at ambient temperatures.

Comments?

fordfreak4life · Apr 25, 2012

Anthony built a dead head system on out race truck.... 4 port dead head no return.... He ran it for a Lil over 4 years and I know of another guy doing the same thing with no issues

Sent from my ADR6325 using Tapatalk 2

Strictly Diesel · Apr 25, 2012

907DAVE said:
LOL

First off, lets think about about getting air into the fuel system, how does it get there?

Either you disconnect something, pull injectors, run out of fuel or.......... you have a air leak or something in the system creating cavitation.

Fuel sloshing in the tank, air entrained in the fuel that is not otherwise removed by something like a FASS/AirDog, foam created by passing fuel with entrained air through a significant restriction.

If you are getting air into the fuel system during normal operation then 100% of that air is being passed through the heads and the chances of that air getting forced through the injectors is much greater than if you were to draw just enough fuel as the engine needs.

There is NO "if", unless you are operating your vehicle in a lab, with an elevated tank with gravity feed that never moves (no sloshing) and doesn't have a return that ever "splashes" fuel in the tank...you have air in the fuel. How much and whether its a problem depend on the truck, whether there are suction side air leaks at quick disconnects or in the tank that are creating larger pockets of "free" (easily removed) air, etc.

If you have a fuel system where the fuel enters the rail and ONLY leaves by passing through an injector, 100% of any air that might be there is going through the injectors with it. If you have a system where a significant amount of the fuel flow passes "through" the rail, exits at the other end and is returned to the tank, significantly less air will pass through the injectors. This is operating under the assumption that the air is not perfectly evenly distributed in the fuel, which if you've ever done testing with clear hose to watch the air bubbles you would see is the case.

As for the "cool fuel" idea...anyone with a regulated return ever feel there fuel tank after a few hours of operation?

That sucker gets pretty warm. This type of fuel system is actually turning your engine into a fuel heater. If you return fuel before it even hits the heads the fuel remains at ambient temperatures.

Not entirely true. Not may people have spent the time and money testing this that I have. We put high quality digital readout gauges in a fuel system, with temperature probes IN THE FUEL FLOW in 6 locations. We drove the piss out of the truck, in both "stop and go" and "highway" situations (long trip, full tank to almost empty without stopping) and tracked the temperatures. We found that the fuel in the tank did NOT significantly increase in temperature over long drives, and that much of the temperature picked up by the fuel as it passed through the heads was dissipated before it made it back to the tank. I would have to go back to the notes and data to remember all of the details...but this testing is the reason I've never put a fuel cooler in my kits.

As for the topic at hand, there is no reason why a 4-corner feed won't work. I personally don't care for regulating pressure BEFORE all of the pressure drop and all of the demand, particularly as far before as an AirDog will be located. I don't think it works well in a stock setup (having the regulator before the injectors) so I wouldn't do it that way in the aftermarket either. In addition, there is a perception that these trucks need big fuel lines and huge fuel flow to make power, which is simply not true. Numerous high horsepower trucks have made big power feeding fuel through the regular 1/8" NPT ports like our current regulated returns are plumbed.

fordf550 · Apr 25, 2012

if given much thought into this system. air in my injectors is the least of my worries. like stated above it has to get there somehow. airdog will remove any amount of air that would be a problem. stock superduty guys go for 300k with a dead head system. i got 140k on my truck and i doubt the motor will make it to 180k. my thought was since i have a airdog there isnt much use in have two regulators in my system, the pump already has one and a regulated return would just put another regulator is the system......pointless is my thinkings. as far as heated fuel heading into the heads, i've seen a regulated return system pull 160 degree fuel from a tank. heat doesnt bother me. either way everbody and there sister runs a regulated return system. maybe its time to try something else

PsRumors · Apr 25, 2012

If you look, others have done what you describe. I thought about it but opted to go regulated return for quicker start ups anytime the fuel system is open, no bleeding, just turn the key, let the pump run for 30 seconds and then crank.

old man dave · Apr 26, 2012

As far as the heat issue is concerned on a regulated return, add a fuel cooler. I also think a regulated return insures fuel pressure throughout the fuel rail, not just at the supply side.

Come to think about it, just how does an AirDog remove entrained air? Is it just a inverted can with an orifice at the top to return fuel/air to the tank?

907DAVE · Apr 26, 2012

Been feeding from all 4 corners for over a year now. Had the fuel system open numerous times and I have yet to have any "air" issues.

OP, I think you are doing the right thing. I am in no way bashing anyone's products, simply questioning something that has become common practice.

Here's a quote from Charles, he's much better with his words than I.

But let me waste some time talking about some fluid dynamics for a second on a system that never changed, and has worked flawlessly for over 4 years.

Okay...

No matter how much fuel you are moving, there will be some potential for fuel vaporization across the 1/8" inlet ports to the heads. The potential here is directly related to orifice size vs flow rate. Well, if you force all the fuel through the heads 100% of the time then the flow rate is always higher for a flow-through setup. Right off the bat you've increased one of the components of turbulence tremendously higher. Secondly, by only allowing 2 of these orifices for this flow, you've halved the orifice area in use, compared to having utilized 4 of said orifices.

So in a flow through, you increase the flow across the orifice, and half the available orifice area.

Combine this with the fact that the average fuel temperature will be much higher by using the fuel as a coolant, passing through the engine heads and you have the full vaporization trifecta of increased flow, reduced orifice size and increased temperature

Perfect if the goal is to provide the injectors with the greatest possible amount of entrained fuel vapor I suppose.

Secondly.....

If we ignore the tendency for creating entrained vapor, and instead focus on what happens to the air that we do have, there's still no practical advantage to flowing-through.

Assuming the entrained vapor is in the fuel stream before the systems at the engine, such as from a restrictive filter, pump cavitation, a line leak or similar, then in each case the injectors will receive the same amount of air whether it all flows through the heads, or only what the injectors consume does.

If there are 100 vapor bubbles per gallon rushing toward the engine, then in a flow through all 100 of them run straight through both heads and the injectors will pull 100 bubbles per every gallon injected. If instead only the portion of flow the injectors are consuming is sent to the heads, then far fewer bubbles actually go through the heads, but the percentage and mixture uniformity remains the same, in that for each gallon injected, the injectors will still have passed the same 100 bubbles in a quad-feed setup.

The only time a flow-through would theoretically be advantageous to me would be after draining the rails, like if you ran the engine out of fuel, or pulled injectors, although to be honest..... even here I have never noticed any change in cranking the truck after an injector swap, or after a filter swap or anything else.

It's simply not so that a non flow-through setup causes air issues. What it does, is allow the use of twice the orifice size, not force all the fuel pump output across half the orifice area 24-7, doesn't use the fuel as a coolant making it even more prone to vaporization and doesn't make the pump move this hot fuel all the time burning the pump up quicker.