Bump for an afternoon read.

 

With regards to the banjo bolt check valve. It will restrict fuel flow through the bolt. Whenever a restriction is removed from any liquid line, the flow will increase. Removing it will improve fuel flow to the heads. I bought new bolts from Ford and they did not have any valves in them. I have not had time to do the mod so I do not even know if I have the right bolts. I suspect I do not since the threads do not match the plugs I removed when I put the cross over line mod in. Will probably do mod tomorrow.

Anyway, I believe the semi check valve bolt design is for the following reason. When the motor stops, the fuel system pressure immediately goes to zero. If you pressurize a liquid then released the pressure quickly, you get "backflow". If the valve is not there, then I believe the possibility exists for the fuel rail to not be full of fuel due to backflow on the next startup. The banjo bolt check valve SLOWLY releases the pressure so the fuel rail remians full of fuel for the next start.

Now I have a special case. I have an Airdog 2 fuel pump. I no longer have fuel return from the engine filter bowl to the fuel tank since the AD2 has it own tank return and fuel pressure regulator. So I removed the fuel bowl return fitting, drilled and tapped it for 1/4-20 threads and put a bolt in it with a copper seal. Worked great! So I have a "dead end" fuel system from my AD2 to the motor. There was no sense in sending treated fuel to the fuel bowl just to have it returned to the tank.

FWIW - I believe the ideal 6.0 fuel system is to have the HFCM pump fuel directly to the fuel bowl, block off the return line as I described above, remove the head's rear fuel rail plugs, tie both heads to a common line, connect that common line to a fuel pressure regulator and connect the regulator back to the tank fuel return line at the HFCM. This does two good things: gives better fuel pressure regulation since the regulator is after the FI and not before and prevents any FI fuel starvation.

DSMMH

 

If the valves in the bolts prevent dry start from the fuel moving away from the injectors, then what replaces the fuel in the fuel rail?

The pump pressurises with in 4 sec of key on.

If there is a dry start then what is replacing the fuel? air??.... fuel leak???

 

cheezit pm'd me a few days ago and said he still had some thoughts on this so I want to see his opinion on the back flow. The fuel rail reaches equilibrium at atmospheric pressure when the truck shuts off but it does not induce air into the rail by releasing the pressure. The pump stops applying force on the fluid, simply P=Ff/Ac, no fluid force=no gauge pressure.

Derek

 

When the pump shuts down, the entire fuel system instantaneously drops to the pressure in the fuel tank. So whether the restriction through the banjo bolts is a 3/8" hole or a pin hole is insignificant because the pressure instantaneously (speed of sound in water +/-) bleeds back to the tank through the pump. You can see that with fuel pressure gauge. The needle drops as fast as the mechanical gauge allows it when the engine is shut down. There's nowhere for air to enter the system and displace fuel at shutdown in a healthy fuel system, so air is not the issue..

When the engine is running and fuel is flowing, the restrictive check valve would most definitely reduce/eliminate pressure surges caused by injector firing, preventing them from traveling further back through the system. (Pressure surges don't care which direction the fluid is flowing.) The waves would only be allowed to run back and forth in the fuel rail. At 1400 m/s (about the speed of sound in water), a pressure wave bouncing back and forth through a 18" long tube may equate to a constant pressure, as far as an injector is concerned.

Maybe removing the restriction allows the wave to run back through the system to the pump or some other restriction back down the like, making the wave return time long enough that it becomes significant to the injectors.

Just a swag. I'm getting a headache.

 

The pressure waves (infinitesimally small) will not move the check valve at all. They are called "normal shocks" in thermodynamics and can be associated with breaking the sound barrier as well. These waves travel within the fluid medium. A check valve is not a hydraulic attenuation device so it doesn't do anything to stop pulse waves. Just my $.02 from an eng. standpoint.

Derek

 

Post deleted. Carry on.

 

The debate is great, but what kind of gains do you guys expect?

Injector demand can easily exceed the flow rate of the HFCM with a tune, then the plumbing becomes a mute point.

 

[quote=w_huisman;8715203]When the pump shuts down, the entire fuel system instantaneously drops to the pressure in the fuel tank. So whether the restriction through the banjo bolts is a 3/8" hole or a pin hole is insignificant because the pressure instantaneously (speed of sound in water +/-) bleeds back to the tank through the pump. You can see that with fuel pressure gauge. The needle drops as fast as the mechanical gauge allows it when the engine is shut down. There's nowhere for air to enter the system and displace fuel at shutdown in a healthy fuel system, so air is not the issue..[quote]





if there is no air in the lines then how can there be dry starts if the fuel is still there, and once the key is on the pressure is back up.

"How can there be dry starts if the fuel is still there?" that is my main question to the ones who feel that removing the valves can create dry starts even though the fuel is still where it needs to be(if there are no leaks)

The only way I can see dry starts is if they quickly start the truck, or a fuel leak

 

I agree, a banjo bolt mod is not the be all-end all of fuel mods, that's for sure. But for the convenience you can't beat it, the previous orifice was 2 @ 3mm vs the new orifice of 3 @ 5mm. The smallest cross sectional area is the banjo bolt, pressure is force over cross sectional area. If you upgrade the banjo bolt then the next restriction is the lines. Instead of building pressure at the orifice of the banjo bolt, you can now be assured that the pressure is being built within the head itself and there is far less restriction at the bolt itself.

I like where this is going, if we can all agree the check valves are useless we might get onto the next fuel restrictions. The stock pump can produce ~100 psi, just decide where you want it to build that pressure... let's think about it.

Derek

 

if we can all agree the check valves are useless we might get onto the next fuel restrictions.
im still not there.
Im gonna sit back a little bit and see what else I can dig up on the issue. Like I said its interesting. I know what they were ment to do. I have not see or had to do any testing in a engine with them gone yet.

 

Story of my life... Mechanic vs. Eng... I know we have a bad rap... But, I am sure glad I grew up on a farm here in S.W. Ontario, I don't only design machines, I turn on 'em.

cheezit, I wanna hear everything you've got. I strive to be a book of knowledge. PM me?

Derek

 

at first I was unsure of the upgrade by the dry start issue, but there is no way there can be a dry start from the way I see it with a normal functioning fuel system, no leaks and pausing after key on,

 

naw no hatered at all I deal with the guy how make this stuff more then I care to sometimes. all of have been good people. funny is when they call they always ask what we know.
my issue is my knowledge of hydrolics and fliud dynamics is limited. I have no issue with stating that at all.

I can agree its a restriction, I dont agree on the uslessness of it. Its there to prevent a backwards pluse from being sent back to the fuel bowl. is it effective in that.. I dont know. I do know that unwanted pules in the fuel system are not wanted and will damage injectors. This valve may very well be a reason that when exhust pulse enters the fuel system it does not spred to the uneffected bank. this tie in to my opinion of tie the rear ports at the back of the head tohether as well. Looping the fuel system together will only serve to add the risk of debree transfer, damaging more injectors if you have an issue with exhaust in the fuel rail, etc. also if we look at the system we would have equal pressure built up in the center between the 2 heads. as pressure is going to be equal to both banks anyway by design.

 

I know you know this but what are the last 2 firing cylinders in the cycle. 6 then 8 correct? They are both on the same side, correct? So 6 takes a good "gulp" before 8 does, then what. A pulse wave traveling at the speed of sound is located how many inches away from the banjo bolts, a spring loaded check valve can't help. You need a hydraulic attenuator similar to that found in the HP oil rail. There are so many pulses @ 2000 RPM that this can be considered a static pressure within the fuel rail, honestly.

Derek