EFI tank discussion

[folkenheath]

Found this from Quantum Fuel Systems.

LS Swap Fuel Pump Hanger for 1973-1991 Blazer, Jimmy, Suburban, Performance Fuel Pump System, QFS-H882 QFS​

Hello Ed,
8an feed line is 1/2", 6an return line is 3/8" we should have these back in stock in the next two weeks

That's a good find for higher HP stuff.

Blazers and suburbans up to around 700 HP NA are easy to retrofit because you can purchase the 87 TBI tanks and sending units and just swap the pump for a 255 LPH Walbro.

If you need the 400 or 450 LPH, the above sending unit is a good option.

Keep in mind, the internal ID of the pump outlet on a 255 LPH Walbro, is very small, its a 5/16" OD plastic barb with a check valve in it. So if you have one restriction that isn't smaller than the pump outlet and then its wide open (-6AN) the rest of the way to the injector rails, you are probbaly fine. Fuel at 40 - 60 psi has a lot more pressure forcing it than a pump trying to suck it out of the tank where you would need 8 or 10 or even 12 AN as the suction line to the pump. In tank pumps are submerged in fuel and only push the fuel, its a major advantage.

Here are some Walbro (TI Automotive) fuel pump flow charts with pressure (PSI) vs flow (GPH) and at different voltages. A gallon of gasoline weighs around 6 lbs, so if you convert it to lb/hr and use 43 psi and 58 psi as the standard flow rates for most injectors, you get these numbers with a 90% duty cycle. This assumes you have the fuel pump wired to a relay with sufficient wire awg and a full 13.5 V is getting to the pump during operation. If not, you will not get the same flow.

Also, this is gasoline, if you are using E85 you can reduce these HP numbers for 40 - 50% and the 255 LPH is not even rated for E85 fuel, you'll need the 400 or 450, or some companies offer a 340 as well for low power E85 builds. Also, this is only 90% duty cycle, if you want more buffer, use a larger pump. However, remember, larger pumps create more heat, it depends on the application and how often you need full fuel flow, a race rig is a lot different than a daily driver. If you are adding boost you can reduce these HP numbers by 20 - 30%, boost uses more fuel/HP to run the supercharger or turbocharger.

You start getting very high flow and you can use twin pumps, dual 255 or even dual 450s can supply a lot of fuel. Holley offers universal in tank pumps that are dual pumps and bolt in the top of the tank, but require custom cutting the tank, or a fuel cell, depending on the kit. I have some of those in stock along with some Walbro pumps.

https://www.volcanomanifolds.com/product/walbro-ti-automotive-in-tank-efi-fuel-pumps

255 LPH (~720 HP at 43 psi and ~650 HP at 58 psi)



400 LPH (~1100 HP at 43 psi and ~1000 HP at 58 psi)



450 LPH (~1200 HP at 43 psi and ~1100 HP at 58 psi)



A factory sending unit for a K5 is easily swappable to the Walbro because you can get conversion fittings from the GM fittings to 6AN or 8AN from Fragola among others.

However, a truck TBI sending unit just has hose barbs, which requires som other adaptor. I have used 45 deg double flare brake adaptors, you could also potential use a single flare 37 deg 6AN sleeve and nut, but be careful.

Here is a truck TBI sending unit I converted to a Walbro 255 LPH and AN fittings back in 2009...

 

[sweetk30]

i used this kit for my fuel lines and no problems from back in 2018 when i built it .

used these compression fittings / barb fittings for the truck sender lines .

3/8" supply and 5/16 return like factory . feeding a L31 vortec and edelbrock pro flo 4 .

also used high pressure fuel clamps in the tank on the sender to pump hose . seen to many pop off of the plastic clips and or cheepy bands . and some high pressure fuel efi hose .

ignore the sniper box / pile of crap .

 

[folkenheath]

If you are going to use hose clamps, Earls "Vapor Guard" hose is made for EFI pressures and uses T clamps style hose clamps. It also is not recommended for sharp barbs, only smooth barbs, so it could work with the factory barb with the correct T clamps. Sharp barbs can damage the ID of the Vapor Guard hose. I don't recommend cutting the stock barb off to add a separate barb fitting, it adds another potential leak point. If you are going to go that route, I would use hard metal tube (such as 3/8" metal brake line) where possible and only use rubber where needed. I do recommend double T style hose clamps when using EFI rubber hose with barbs, double clamps gives more holding power.

For fuel tanks with regular Walbro pumps, the stock TBI/EFI tank and sending unit/pickup assembly work fine, with the correct pump swapped in.

In addition to C/K trucks (R/V), this is also true for most 80s GM car platforms that later had EFI, G-body, F-body, B-body?, S10 pickups, etc...

1987 Short bed tank - 16 gal, Dorman #576302, Spectra #GM11C
1987 Long Bed Tank - 20 gal, Dorman #576336, Spectra #GM1C
1987 Truck Sender Left Side - Dorman #692027, Delphi HP10255 (w/TBI pump)
1987 Truck Sender Right Side - Dorman #692044, Delphi HP10256 (w/TBI pump)

1987 K5 Tank - 31 gal, Dorman #576313, Spectra #GM14C
1987 K5 31 gal sender - Dorman #692033, Delphi #HP10026 (w/TBI pump)

1987 Burb Tank - 40 gal, Dorman # 576349, Spectra #GM25C
1987 Burb 40 gal Sender - Dorman #692034, Spectra #FG12M

 

[folkenheath]

That's open for some debate, but it is an obstacle to flow and pressure that the pump could only recover by having reserve capacity and pressure

I think it depends, there is a third option too, velocity.

If you are trying to pull fuel through to the pump inlet, it's difficult and the pressure delta may be low, and it could induce cavitation from the low pressure restriction.

However, if you are trying to push the fuel through at 58 psi with an in tank pump, it becomes multiples easier and if it's a short restriction at high pressure with an incompressible fluid like fuel with a fixed volume pump it may just increase the velocity in that short distance and not affect flow.

However, if you take that same restriction and keep it for a long distance it may reduce flow and start building up heat as the pump draws more current to attempt to overcome it.

If you look at the ID of the pump outlet, not the OD of the pump outlet, you will likely find it's quite small, if it's a very short restriction and it isn't more restriction than the pump outlet, it may not matter. However, if its multiple restrictions and/or smaller than the pump outlet and or a very long continuous restriction, then you likely have a problem.

I do not think you will have any issue supplying fuel through that orifice with that pump for 500 HP. However, if you are doubting it, do the flow test in the old gallon bucket and see how long it takes to fill 1 gallon or 5 gallons. Then consult the chart above and see how far off you are, keep in mind if you only supply 12V and not 13.5 don't use the 13.5V numbers.

You'll also see that these gerotor style pumps don't drop flow off suddenly with pressure increase like a vane style pump would, at 12V its about 76 GPH at 0 psi and 74 GPH at 10 psi. However, you won't know what the pressure is on the other side of that restriction, but you can estimate it based on the flow numbers. It drops to 68 GPH at around 20 psi for example, using the solid blue 12V pressure/flow curve in the above 255 LPH chart.

If you are using 58 psi and that orifice only becomes a flow restriction for that pump below 10 or 15 psi, it won't really matter.

Also, tanks inc sells that same setup with a 450 LPH pump, so either they are selling a mismatched setup, or it doesn't matter, a simple flow test will prove it.

Everything I can find shows 1/2" fuel line needed for 550 hp with a 46 GPH (175 LPH) pump. I would not want fitting smaller than 1/2" (-8) if I was designing the system. What you may be finding is the limitation of the stock sending unit arrangements. There is a reason for fuel cells in race cars.

This one comes with -8 AN fittings:

Pardon Our Interruption

That is the case for a low pressure carbureted external pump suction style fuel system. That is not the case with an in tank pump with 40 - 60 psi forcing fuel through the lines the entire path to the injectors. You can feed 700 HP through a 3/8" line with only a 5/16" outlet on the pump, and more through an entire 3/8" line from the pump too.

Now, if you have an external pump then you definitely need a larger line on the suction side of the pump, 1/2", maybe even 5/8 or 3/4". However, at EFI pressure (40 -60 or more) you can leave the supply line smaller once the pressure is there forcing it through the line.

An 8AN line at 58 psi can easily feed over 1000 HP of gasoline.

Now, you start talking E85 or especially methanol, then these lines are too small.

 

[76zimmer]

Excuse my ignorance….
Does feeding, lets say a 500 hp 454 at 5000rpm differ from feeding a 500 hp 383 at 7000rpm? Does rpm and c.i. matter or is it just BSFC?
Does it matter if those 500 horses are carb fed or F.I. fed or is it all about the amount of fuel delivered?

 

[folkenheath]

The BSFC is the main culprit. So the HP, the fuel used, the powder adders, the engine efficiency, all play a role. So yes there could be a small difference between those two engines, however, if they both have old school combustion chambers that both want 36 degrees of timing they will probably be pretty similar.

Now, you take a modern combustion chamber like a 4 valve pent roof or even an LS chamber that only wants 28 degrees of timing, has less friction in the piston rings, and less pumping losses because the heads flow 350 cfm for a 500 HP engine and you may notice a difference in BSFC. However, it still won't be as big of a difference as say, taking 50 HP just to turn a supercharger or having 2 psi of backpressure to spin a turbine. Boosted applications usually also need to run richer to be safe which uses more fuel per HP.

Here are the BSFC I have as "defaults" for my app, you can also select a custom BSFC in the advanced portion...