How it Works - Fuel Selector Valve (FSV) and IDI Fuel Math AKA "What fuel pump should I run?"

[hacked89]

Here is a summary of my recommendations from this thread, the fuel math, and the FSV disassembly, cutaways and measurements.

I'll add it to the first post as well.

1. If your injection pump/engine builder informs you that your build requires more than 30gph then delete the FSV, it's internal supply port is 1/4" and you will encounter fueling instantability.

2. If you require up to 70gph (66 to be exact but we are rounding up) you can stay 3/8" supply with a pump whose fueling curve supports it at the documented pressure. If you require 100gph or more (92 to be exact same rounding up to numbers which correspond to pumps) then you should move to 1/2" supply line because otherwise you will be stacking multiple pumps, require higher end pumps to maintain the pressure to fuel flow curve, and have more pressure to flow instability.

Evidence with notations top right:

Stock fueling at stock lift pump psi aligning with original posts

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With a 70gph requirement such as my T04Z build

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With 100gph requirement, it's clear why you start having fueling stability issues on 3/8" lines, needing to stack pumps, and incurring challenges of maintaining the pressure needed for the flow requirements.

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Finally, check out the significant difference of a 1/2" line maintaining flow requirements at an achievable pressure to flow curve ratio for the electric pump

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Remember, you must compare this math to the flow benchmarking of the electric pump in order to choose the appropriate electric pump. In general, the higher the pressure, the more amp draw on the pump, the lower the flow rate.

Here is the Gsl392 flow graph i posted earlier

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Sent from my SM-G955U using Tapatalk

 

[franklin2]

I always wondered if it will be possible or practical to have a fuel pump for each tank (with a check valve to prevent backflow) so when you switch from one tank to the other it turns on the respective fuel pump turns on and the other turns off. Then you could use the selector valve to control the return system and fuel gauge.

That is exactly what the factory did on the 84-up 460's with the 4bbl carbs on them. They called it a "hot fuel handling" system. Electric pump in each tank. Power to the pumps was selected by the dash switch or a relay switched by the dash switch, and the other pole of the dash switch switched the exact same 6 port pollack valve they used on our idi trucks.

They used a tee fitting at the carb with a orifice. That metered a certain amount of fuel to return to the tank being used all the time. This kept the fuel from vapor locking. If you can find parts and sending units for a 460, this in tank pump system is what you will run into.

 

[mblaney]

Here is another option for a FSV. My son has a 1987 F150 that has very simple fuel valve. Basically, the valve is a bellows fed from each fuel tank, and when one lift pump is powered the fuel pressure (5 psi) shifts the bellows and redirects the return line. Google DORMAN 911000. This valve has no electrical connections - fuel sender and pump electrical are completely separate of the valve. https://www.rockauto.com/en/moreinfo.php?pk=8165048

 

[jpww]

The marine and aircraft worlds have quite a few options from mild to wild that could be quite useful once we are past the point of wanting to make stock parts work. Might take a bit of custom plumbing...

Mild / simple - https://www.boatid.com/groco/1-2-np...MI8d2zh63z7QIV5x6tBh065QiJEAQYASABEgLN4_D_BwE

Wild - http://www.westcoastoffshore.ca/6-Port-Polished-Super-Fuel-Valve-06-2100-P3901.aspx

I am hoping to end up with three chassis mounted tanks on my truck but I build at the pace of frozen molasses so it will be a while before I have anything to post with pictures.

HTH

J

 

[Clb]

@Colton Stevens

 

[franklin2]

Here is another option for a FSV. My son has a 1987 F150 that has very simple fuel valve. Basically, the valve is a bellows fed from each fuel tank, and when one lift pump is powered the fuel pressure (5 psi) shifts the bellows and redirects the return line. Google DORMAN 911000. This valve has no electrical connections - fuel sender and pump electrical are completely separate of the valve. https://www.rockauto.com/en/moreinfo.php?pk=8165048

I thought those valves required more than 5 psi to work? Actually I don't have the specs on that valve, but Ford always used them in the fuel injected trucks that ran 35-40 psi.

 

[IDIBRONCO]

Maybe they only need 5 PSI to switch? The pump puts out more than that and the engine wouldn't run very good, if at all, if the pressure drops to even close to 5 PSI.

 

[nelstomlinson]

The Groco FV65038 valve looks like the way to go. Plenty big, no electronics. We would just have to rig the dash switch to switch between the two fuel senders.

 

[franklin2]

The Groco FV65038 valve looks like the way to go. Plenty big, no electronics. We would just have to rig the dash switch to switch between the two fuel senders.

Hmmm... $117.60 valve with a bunch of wiring and new fuel lines and fittings. Or a f26e 38 gallon tank for $159.89 plus modifying the sending unit and splicing the original fuel lines at the old pollack valve. Both simple and reliable. Cost will be close, you will have to buy straps for the tank and lots of fittings for the Groco valve. Both good solutions though.

 

[nelstomlinson]

I kind of like the idea of having two tanks. I do plan to replace the back tank with the 38 gallon version someday. I like the idea of having a really long range. I could drive from Fairbanks to Deadhorse, and most of the way back with the 50 or so gallons in those two tanks.

 

[IDIBRONCO]

I kind of like the idea of having two tanks. I do plan to replace the back tank with the 38 gallon version someday. I like the idea of having a really long range. I could drive from Fairbanks to Deadhorse, and most of the way back with the 50 or so gallons in those two tanks.

This is why I'm going to use both tanks and pump fuel from the rear into the front tank, which is the only one that works. Although there is a real possibility that I won't be driving anywhere close to Fairbanks or Dead Horse.

 

[mblaney]

I thought those valves required more than 5 psi to work? Actually I don't have the specs on that valve, but Ford always used them in the fuel injected trucks that ran 35-40 psi.

My understanding is that the in-tank lift pumps are 5 psi, the single high pressure pump is located after the FSV and is 35 - 40.

 

[nelstomlinson]

Although there is a real possibility that I won't be driving anywhere close to Fairbanks or Dead Horse.

The mosquitos will be disappointed.

Seriously, someday some of us should do a Deadhorse to Kenai camping trip. I'm hoping to go in the summer of '22.

 

[IDIBRONCO]

Seriously, someday some of us should do a Deadhorse to Kenai camping trip. I'm hoping to go in the summer of '22.

It sounds like fun, but last I heard, you need a passport to drive from the lower 48 to Alaska. The last time I had one of those things, I ended up in Iraq.

 

[Clb]

That and the fukking crown h8's handguns so you will only get 7 days in country.
edit
Fairbanks to keni We missed the sw section when we went.
End edit
Fuel stops were awesome (right about every tankful up popped another) however no way a one tank rig would be comfortable unless maybe a 38 gal...

The Ak. Natnl. Bird

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