Higher HP OBS fuel system

[Derek@Vision Diesel]

If they are at the same level there would be no problems. Remember there will be a slight vacuum on the pump inlet line if the pump is mounted higher than the sump.

How does a check valve stop this issue, think flow direction.

Didnt see all of this the first time I read it. The pump will sit at the same level or lower than the front tank sump.

 

[907DAVE]

Maybe I am not following completely here.

Imagine a fuel pump connected to a fuel jug with fuel inside, another that is empty. Does the pump care that the jug closest to you has fuel in it and not pull any air from the empty jug?

Unless the pump is LOWER than the sump there will be a vacuum on the suction line, and the easiest way to break vacuum is to introduce air.

See what I am getting at?

 

[907DAVE]

Gotcha, I appreciate what you are trying to do, just not sure its the best option.

 

[Derek@Vision Diesel]

Maybe I am not following completely here.

Imagine a fuel pump connected to a fuel jug with fuel inside, another that is empty. Does the pump care that the jug closest to you has fuel in it and not pull any air from the empty jug?

Unless the pump is LOWER than the sump there will be a vacuum on the suction line, and the easiest way to break vacuum is to introduce air.

See what I am getting at?

I sure do.

You are thinking if the rear tank is 100% empty and even though the front tank is 100% full that it could still get air from the rear tank? There will be a constant flow of fluid until the front tank is empty though, wouldnt there? Wouldnt the pull pull out of the front tank before sucking air out of the TOP REAR tank?

The pump will definitely be mounted below the front sump. If this theory does not work, I will have it return back to the front tank and delete the rear tank all together.

 

[907DAVE]

Its a gamble. Throw a vacuum gauge on the suction side of the pump and see whats up. If there is any vacuum I would reconsider the options here.

I dont know if i would be too fond of a pump that sits lower than my fuel tank either, just wont look right...haha.

Again, just my opinion. It would be a killer setup if it worked well.

 

[Derek@Vision Diesel]

Its a gamble. Throw a vacuum gauge on the suction side of the pump and see whats up. If there is any vacuum I would reconsider the options here.

I dont know if i would be too fond of a pump that sits lower than my fuel tank either, just wont look right...haha.

Again, just my opinion. It would be a killer setup if it worked well.

Definitely! I was trying to think if the bottom of the rear tank is HIGHER than the top of the front tank. I could also gravity feed from bottom of rear into the top of the front, that would solve all problems with the pump sucking air.

I have 2 sumps. I could put them both on the same tank. One of them is letting fuel into the front tank, one of them is letting the pump suck the fuel back out. The just have my -10JIC welded to the rear tank in order to let the fuel into the front one.

Could also just keep one sump and weld a -10 JIC onto both tanks and connect them that way. And then have the Sump in a different location for suction

 

[907DAVE]

As long as the fuel tank is well sealed and fill/ vent tubes dont leak that tank could run that full without issues. It would be bad news on any gasser with a charcoal can or EVAP system however.

I think that is the lesser of the two evils. But, if the bottom of the rear tank is NOT higher than the top of the front there is going to be un-usable fuel and reduced capacity. At that point it might be simpler to just plumb the front tank into the new fuel system and have a transfer pump to move fuel from the rear to the front tank.

 

[907DAVE]

Your last idea might be the winner also.

 

[Derek@Vision Diesel]

I think my last idea is the winner also, I've decided that is what I am going to do to save an headache of switching it up later.

The two tanks will be connected with JIC fittings welded to the tank, I will return all fuel to the rear tank, and I will feed the A1000 with a sump on the front tank.

Boom bam done... time for bed.

its past your bed time anyway dave, you've got a single cab to put into the 10s soon.

 

[907DAVE]

Haha, whatever.

Let me know how it works out!

 

[907DAVE]

Also, be sure to tie the tank vents together to equalize pressures, and dont worry abut returning to the rear tank - it wont make any difference.

 

[Derek@Vision Diesel]

the front tank would overfill wouldnt it, because the back tank sits quite a bit higher, maybe even completely above the front tank

 

[Tom S]

As long as the fuel tank is well sealed and fill/ vent tubes dont leak that tank could run that full without issues. It would be bad news on any gasser with a charcoal can or EVAP system however.

I think that is the lesser of the two evils. But, if the bottom of the rear tank is NOT higher than the top of the front there is going to be un-usable fuel and reduced capacity. At that point it might be simpler to just plumb the front tank into the new fuel system and have a transfer pump to move fuel from the rear to the front tank.

Sounds like a good ideal to me.

 

[davey99ps]

To me this seems overly complicated. I got rid of my front tank, an stock rear tank, then put a 38gal tank in the rear an mounted my filters where the front tank was. I can go roughly 600mi on that much fuel, which I would think is plenty. To me it was the most basic an simple solution

 

[Derek@Vision Diesel]

To me this seems overly complicated. I got rid of my front tank, an stock rear tank, then put a 38gal tank in the rear an mounted my filters where the front tank was. I can go roughly 600mi on that much fuel, which I would think is plenty. To me it was the most basic an simple solution

That is more simple than welding a bung on the bottom of each tank and connecting them together?

I guess we will see if it works or not, but the tanks are completed and not leaking.... now time to get the truck running.

 

[Chrisf97305]

Yes we are using the 1/8" ports with 3/8s feed. I just want to give the most volume possible. Making it easier on the pump and not worrying about pressure drop.

Has anyone found the TRUE limit of the OBS fuel system using the stock selector and lines back to the tank?

Is anyone running 300cc+ with the stock selector valve to the tank all being stock?

This is a customers truck, we just simply decided to get rid of all the start pieces in an effort to supply the injectors as best we could

These fittings here go in place of the bandjo bolts on the back side of the heads. I used 3/8 hard lines to connect them. you could just as easy use 3/8 hoses. Then I use the 1/8 fittings for my fuel gouge.

 

[Derek@Vision Diesel]

Thats a beautiful setup, hoping the 1/8" ports are large enough for what we want though. With the stock downpipe location it makes it a little tight on that passenger side

 

[Strictly Diesel]

My race engine, the engine in the WOP Lightning and the 7.3L that was in the WOP dragster were all fed through the 1/8" ports. I'm sure that there are many others big HP trucks plumbed that was as well. Shouldn't be a problem.

 

[Derek@Vision Diesel]

Well everything is assembled and installed in the truck, ran the a1000 yesterday to test for leaks and fire the truck up once before we put it all back together.

Seems to be working pretty good so far, but still unsure how it will handle parking on steeper hills

 

[Strokersace]

I think that is the lesser of the two evils. But, if the bottom of the rear tank is NOT higher than the top of the front there is going to be un-usable fuel and reduced capacity. At that point it might be simpler to just plumb the front tank into the new fuel system and have a transfer pump to move fuel from the rear to the front tank.

This is what I'm going to do at some point. I want as much fuel capacity as poss for long trips, so I have the factory front tank, 50 slip tank inbed plumber into front, and a 38 gal rear. I'm going to install a 38 gal SD midship tank in place of the factory front soon. At that time, I'm going to remove the selector valve from the system. Everything will be ran off the front tank. Going to install a sump into front, keep slip tank gravity fed into front, and going to install a transfer pump to move fuel from rear to front only when needed.