Higher HP OBS fuel system

[Derek@Vision Diesel]

Have a truck with large enough injectors that the stock selector valve and fuel lines were not going to cut it.

The original idea was to use 2 sumps. The rear sump would gravity feed to a T on the front sump, with hopes to keep the 2 tanks tied together as one large one. Then we would return all fuel to the rear tank (because it is higher).

Purchased 2 sumps and all the gear and went to install, a sump will not work on the rear OBS tank.... or at least not the sumps we got.

The sumps we have are 5" diameter on the out most O-ring, the largest we can have is 4" on the out most o-ring to use it on the rear tank.

Question 1: Has anyone found a sump that will work or does someone sell one no larger than 4" diameter on the out most o-ring?

Question 2: Whats another method people are using on the OBS trucks while hopefully keeping the stock amount of fuel on board (one large tank? 2 pick up tubes with a manual selector valve before the first filter?)

Thanks!:fordoval:

 

[Clouse2411]

I went with a single 38 gallon tank, with a 90 degree an fitting welded into the bottom of the tank.

 

[Derek@Vision Diesel]

I went with a single 38 gallon tank, with a 90 degree an fitting welded into the bottom of the tank.

And you installed that in the rear? Can you link me to where you found that tank and maybe a picture or two of your installation?

How did you work the sending unit or did the new tank come with its own fuel level sender?

 

[Derek@Vision Diesel]

I like your idea Austin of welding a larger fitting to the bottom of the tank, might do that to feed the front tank and run a sump out of the front tank

 

[Chrisf97305]

ok here is something to think about. you say that you can not get enough fuel through the selector valve. are you still using the 1/8 supply fittings going into the engine? If there is ever a bottle neck in the fuel system I think that it would be there.

 

[smokedout250]

I went with a single 38 gallon tank, with a 90 degree an fitting welded into the bottom of the tank.

We did this to a wheelin rig it wasn't a powerstroke, but we need the fuel for the cummins... Worked great... We used a bronco tank and fab'd everything up our selves even the fitting on the bottom


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[Derek@Vision Diesel]

ok here is something to think about. you say that you can not get enough fuel through the selector valve. are you still using the 1/8 supply fittings going into the engine? If there is ever a bottle neck in the fuel system I think that it would be there.

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

 

[Tom S]

In tying the tanks together you need to consider gravity feeding when parked on a slope like a steeper driveway and overfilling the low tank.

 

[907DAVE]

Weld in sump pointing to the rear.

Will you be able to fill both tanks completely when plumbed in this fashion?

 

[MossBack]

My thought was sump both and run selector for return line.

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[old man dave]

We did this to a wheelin rig it wasn't a powerstroke, but we need the fuel for the cummins... Worked great... We used a bronco tank and fab'd everything up our selves even the fitting on the bottom


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Spectra Premium F26D or F26E, each 38 gallon rear replacement tank, comes with mounting hardware. RockAuto.com, last time I looked about 135-155 plus shipping. F26E has vent bracket, F26D does not, have no idea what bracket is. Discount code for 5% discount is 94832577809431, enter code in "How did you hear about us" box when checking out.

I'm going to try a prefilter, fuelab pump and check valve for each tank, switching pump to select tank, a single output filter and use the old selector valve for the return line. Undecided on using a straw or a sump.

Four stock selector valves in parallel would have about the same cross-sectional area as an AN-10 line (5/8").

 

[Derek@Vision Diesel]

Weld in sump pointing to the rear.

Will you be able to fill both tanks completely when plumbed in this fashion?

I think what will be the easiest is to weld a -10 90* JIC fitting to the bottom of the rear tank. That will gravity feed the front tank and I will return everything to the rear with a dedicated return line.

The selector valve will only be used to monitor fuel levels in each tank.


I could see parking on a severe slope being an issue with over filling, we will just have to see. Could also re do the system later on if this does not work.


Dave, what did you mean with welding in the sump pointing to the rear? I am not following you there bud

 

[907DAVE]

One of deezz...

http://www.full-race.com/catalog/images/fuel sump.jpg

Pointing to the rear because levels will be lower in that tank because of the plumbing, this way it will grab fuel under power.

 

[SSpeeDEMONSS]

Run a check valve between the rear and front tanks that way fuel can only drain out of the rear and not fill it.

Garrett

encrypted with an enigma machine

 

[Derek@Vision Diesel]

One of deezz...

http://www.full-race.com/catalog/images/fuel sump.jpg

Pointing to the rear because levels will be lower in that tank because of the plumbing, this way it will grab fuel under power.

You are suggesting to put this on the rear tank?

The front tank will be fully operational as a normal tank with a sump in the lowest point. That sump will have a T fitting on it so the rear tank can connect up right there. The hope is it will generally use all the fuel from the rear tank before starting to use the front tank, so you can watch your fuel level on the rear tank, then switch the selector in the cab to monitor the front tank.

You should be able to fill the rear tank up with diesel and have it trickle into the front tank over time.

Shouldnt I be able to just weld a JIC fitting to the lowest point on the rear tank, its not important if we can get every last drop out of it, even if we only use 7/8 of the fuel is good enough

 

[907DAVE]

What happens if the rear tank runs dry?

 

[Derek@Vision Diesel]

Run a check valve between the rear and front tanks that way fuel can only drain out of the rear and not fill it.

Garrett

encrypted with an enigma machine

Forgot to add this, with a one way check ball between the tanks haha!

 

[Derek@Vision Diesel]

What happens if the rear tank runs dry?

THey are connected together as one, if the rear tank runs dry then it is just sucking from the front tank only and the rear just sits there as an empty tank.

Or are you saying that could introduce air into the system if that were to happen? With a check ball in line, as soon as it was empty, the ball would close and basically cut that tank off, right?

 

[907DAVE]

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.

 

[Derek@Vision Diesel]

If they are at the same level there would be no problems.

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

The back tank sits much higher than the front tank. So the only reason the check valve is there is to prevent any fuel from the front sloshing back or being pulled back under acceleration.

The rear tanks purpose is to refill the front tank basically, and all unused fuel from the engine will get sent to the rear tank (which will then gravity feed back to the front)