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

[hacked89]

On episode 1 of how it works and as author of the facet beat down meme, I thought I'd share some insight, math and pictures I took when putting together the fuel system for my T04Z.

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#### Too Long / I didn't read the post #####

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.

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Let's start with repeated statement on the forum #1:
"if you run the electric fuel pump with the FSV inline I heard/saw/read someone else say on the forum, that inside the FSV it will bottleneck depending on your GPH requirements.
True or False?.. Let's take a look

Here in the vice is our friend the FSV, about to meet its maker

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Crack it open to see how it works.
Now we have two halves here.
The first half is an electric motor that turns a rotor which is attached to the plungers. The plunger rotor assembly rides on electric contacts for position, and then either cuts off the fuel from the front tank or rear tank.

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A number of opportunities of failure here.
Stuck on the contact pads, motor goes bad, spring goes bad, orings crack and fuel is now mixing between tanks etc

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Now in the one picture you can see the primary supply and return ports to the factory lift pump, which look very small.
Next we will half that again in a cutaway and measure the ports.

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FSV Supply: 1/4"
FSV Return: 1/5"

Factory supply hard-line: 3/8"
Factory Return hard-line: 5/16"

what's the factory lift pump specs?
At cranking:
4-7psi to the IP @1/3 pint per 10 seconds
Or 15GPH cranking to the IP and
Maximum Free Flow Rate (gph): 30
Maximum Pressure Range (psi): 5.75

30gph is the target here.

I also cross calculated the fuel flow requirements and got 30gph for a 7.3NA

Now the length of the truck @3/8" line and 5psi pressure, what do you think the fluid flow is?
-> 28gph

Then you may say, uh oh the FSV is 1/4" supply.
Well, guess what 1/4" tube flows at 15ft to the end point?

-> 30gph

This isn't all by chance of course that all these numbers line up.

But now let's throw in modifying the IDI, adding a big turbo, what are the requirements?

My specific builds injectors, ip, and turbo will require 70gph max.
Here's my hungry Db2.

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The injection pump takes 5psi at the inlet, creates pressures of up to 5-6k psi and the injectors open at 1700-1900k psi.

That's not going to happen through 1/4" line.
Also remember you can increase pressure to increase flow with a high pressure electric pump, but you are going to want to regulate it down right before the IP to 5-10psi depending on your ip specs.


Looping back to our original forum lore testing part 1.
"is the FSV going to be a constraint in a performance build?"

Answer: Yes - it's designed to meet factory specs at max, not exceed maximum factory components of the wholistic fuel system. Sometimes you get lucky and certain components on a vehicle may exceed certain individual component constraints, not this one.

Part 2: In reply post.



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[hacked89]

Part 1 Continued:
Here is a GIF of how the plunger system works and my thumb is on the rotor that the electric motor connects to
https://imgflip.com/gif/4rry8d

Here are the o rings that seal the plungers and another point of failure

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Part 2: What electric fuel pump should I go with? "I don't want to hear about math or how it's unique to my setup just tell me the pump to buy"

Here are a few suggestions, there are plenty of pumps out there that would work fine.

Ths most accurate answer is it depends and to pay attention to the free flow GPH VS pressure and what psi your vendor of choice would like you to put to the inlet of the pump if it's modded. Ultimately it comes down to what your peak GPH requirement is and not falling for the marketing tactic of @zero pressure flow which I see happening here often unfortunately where people buy a pump which says 35gph at free flow. Once you are at pressure down goes the GPH.

First thing to keep in mind, the pumps below are HVLP(high volume low pressure) pumps and they are gravity fed. You usually want them 2ft-18inches from the tanks or as close as you can get them and have them push the fuel forward. If you have them at the front of the vehicle, you will burn them out and then see people make 1 star reviews.

If you are N/A to mild turbo build I would go holley red 12-801-1 with adjustment screw @5psi. This will flow 67gph which will sustain your peak requirements, rest will go through the return system which you can put a gauge on and should be 1-2psi.

You can also go with Mr Gasket 95 in the situation build above, which will flow 65gph at that pressure.

For mild to higher turbo builds you can go with Mr Gasket 105, which comes with a regulator which is set at 14psi, and bring it down to 9 psi at 70GPH but depends on your IP builder talk to them about the desired input psi.

Me, I went with the Gsl392 which may cause an issue for my hungry T04Z and IP but we will hook up a bunch of gauges and monitor.

 

[The_Josh_Bear]

Great work!

How did you get to 70gph for your setup based on that graph? Or was that info from Wes?

 

[hacked89]

Thanks Josh.
I got the more detailed injector and pump specs from Wes that I needed to do the conversions and math on my side.

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[Golden Helmet]

Out of curiosity, if the stock FSV is proving to be a bottleneck, are there any other options we could jerry rig to our trucks besides converting to a single tank? Maybe something off a big-rig that does the same job but has larger ports?

I love your write-up and especially the inclusion of the nerd details, thank you for doing that! Very interesting read

 

[quickster]

Yeah there is. Looking for it right now

 

[quickster]

Manual Selector Valves / Electric AND Mechanical fuel pumpspage 2 in idi tech at top of the page

 

[Farmer Rock]

I always wondered why a fella couldn't just get a Y connector to connect the feed lines from both tanks into one line and bypass the fsv and switch.




Rock

 

[IDIBRONCO]

Part 2: What electric fuel pump should I go with? "I don't want to hear about math or how it's unique to my setup just tell me the pump to buy"

This makes it sound like you made this write up for people on Face Book.

 

[IDIBRONCO]

I always wondered why a fella couldn't just get a Y connector to connect the feed lines from both tanks into one line and bypass the fsv and switch.




Rock

You could, but you'd still have to deal with the returned fuel.

 

[Thewespaul]

Awesome work! A general rule of pump I've been giving guys for flow requirements is to consider the stock 30 gph mech pump to be matched for a 50-60cc pump, if you have a 130 pump pusing 150cc at peak, youre going to need at least a 90 gph pump to keep up, I prefer to oversize the fuel system and run a bypass style regulator to return any of the fuel not consumed by the ip, it doesnt overwork the e pump by using a bottleneck style regulator and keeps the fuel cooler as well. Thanks for sharing!

 

[Farmer Rock]

You could, but you'd still have to deal with the returned fuel.

I thought about that,but I wasn't sure if at that point you could just return to one tank,or split it up between both tanks with another Y connector.I am not sure what I want to do to my 250,since the PO disconnected the fsv switch and bypassed the mid tank completely,so I have to hook everything back up,and I want to keep it simple.



Rock

 

[The_Josh_Bear]

I thought about that,but I wasn't sure if at that point you could just return to one tank,or split it up between both tanks with another Y connector.I am not sure what I want to do to my 250,since the PO disconnected the fsv switch and bypassed the mid tank completely,so I have to hook everything back up,and I want to keep it simple.



Rock

The problem with connecting the two tanks in a Y setup is that once one is out of fuel, all you'll get is air, because air is much easier for a pump to pull than fuel. So you'd have to be much more diligent about being low on fuel than those with separated tanks. Add to that pulling grades with around 1/4 tank and you could get in trouble there too.
I've often wondered how to make a valve that shuts off when air is present but open with fuel but it all sounds like even more complication and points of failure than the FSV to me.

38 gal bronco tank for a single is super cheap for what you get...only about $125 with free shipping at Rock Auto last I checked. And there is a 5% OBN discount code here somewhere too.

 

[IDIBRONCO]

I thought about that,but I wasn't sure if at that point you could just return to one tank,or split it up between both tanks with another Y connector.I am not sure what I want to do to my 250,since the PO disconnected the fsv switch and bypassed the mid tank completely,so I have to hook everything back up,and I want to keep it simple.



Rock

If you return to one tank, then it will overflow before both of them are empty enough to be refilled. You'd be drawing from two, but the return from two tanks would be going into just one tank. If you try to use a Y to split the returned fuel back to both tanks, I think that you'd still have trouble, but maybe not quite as much as returning to just one tank. In the return line (the one from the engine back) the returned fuel is basically under no pressure. This means that it flows. Just like water, it would go to the path of least resistance. Since the rear return line would be longer, and have a slightly higher resistance due to friction, I think that the fuel would tend to return to the front tank faster than it would to the rear tank. Personally, I wouldn't try it. To me, the transfer tank/pump is easier to deal with. Once it's in, you know that it will work.

 

[hacked89]

My system is 3/8"-AN6 all the way now and single tank.
I'll be running a bypass regulator that is tied into the return system, with pressure gauges on the supply and return, and also an electric in line flow meter that is tied to an LCD screen in the truck which shows the instanteous flow rate. We will then be able to track and see real world metrics.

This disassembly, cutaways and measurements prove that if you are trying to do more than 30gph through the FSV, you may start to see odd fuel issues or symptoms. Because the distance from the FSV to the factory mechanical lift pump is at 1/4" internal supply diameter which results in 30gph, which matches the flow rate design of the factory lift pump.

@Thewespaul
Wes, have you seen funny issues pop up with trucks in this FSV scenario with your 130cc or higher at peak conditions? or most people arent pushing the trucks hard enough to know?

Also to flow 100gph under the pressure needed those pumps you are describing normally need 1/2" supply, and you'll notice most have - 8an fittings versus the Gsl392 and other pumps we are talking about being - 6AN. You can adapt them down to 3/8" but the pressure goes up and you end up in the 70-80gph range anyway.

Take the holley 12-890 as an example:
GPH
@43PSI - 76GPH
@60PSI - 70GPH
@8PSI - 100GPH

In this scenario on 3/8" line you would probably have decent psi due to the smaller diameter tubing so be at 70-80gph and then regulating down





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