Fuel line size

[Cobraman]

I have run an6 to everything in the engine bay then realized the the ffr line is not 3/8. But the I think messed up with 750 bawler Carburetor on 408 with estimated 500hp I should probably run 1/2 supply line from intank fuel pump to regulator or can stay with 3/8?

[Papa]

You're kind of at the tipping point at 500hp. I see some charts that show 3/8" up to 500hp and some that show 3/8" up to 450hp. I would expect that for street use, 3/8" should work okay. What does your engine builder, if you have one, recommend?

[Cobraman]

Because I'm street driving it mostly they thought 3/8 would fine, so I guess I'll eliminate the 1/4" return line and make the 5/16 the return and run an6 to the back to the fuel pump 3/8 outlet. I have just enough line to make it work.

[Papa]

If you're running a carb, why do you need a return?

[Mike.Bray]

If you're running a carb, why do you need a return?

He's thinking someday he'll enter the 21st century;)

[cv2065]

He's thinking someday he'll enter the 21st century;)

Actually, Aeromotive suggests a return on their A1000 carb system. :p

[cv2065]

I have run an6 to everything in the engine bay then realized the the ffr line is not 3/8. But the I think messed up with 750 bawler Carburetor on 408 with estimated 500hp I should probably run 1/2 supply line from intank fuel pump to regulator or can stay with 3/8?

I ran 1/2" (-8AN) flex lines to and from. As Dave said, you are at the tipping point at 500HP. Here's a good reference from Summit.

https://help.summitracing.com/knowledgebase/article/SR-04879/en-us#:~:text=We%20recommend%20you%20install%20a%2010 0%20Micron%20In-Line,popular%20option%20for%20building%20a%20perfo rmance%20fuel%20system.

[CW_MI]

I plan on going -8AN , same as you. In fuel delivery, I've always had the mindset of too much rather than just enough.

[Mike.Bray]

You have to be careful when sizing as not all -6 or -8 lines are the same. Tube is measured on the OD so -6 or 3/8" fuel line tube @ 0.028" WT will have an ID of 0.319". -8 will be 0.44" ID

However, in theory -6 AN hose should be somewhere around 3/8" ID but they're not all the same and when you add Teflon liners like you should for today's ethanol blended fuels it can be considerably less than 3/8" ID. I have three or four different brands of -6 PTFE lined hose in my garage and they vary widely in ID size.

Anything more than 450 HP or so just go with -8 and don't worry about it.

[edwardb]

Deleted EFI related content. Thread is about a carb'd setup. Says so in the first post. Duh.

[gbranham]

He's carbureted, but I agree with your logic, Paul.

Greg

[Nigel Allen]

The OP has said that he is running a carb, so I am thinking much lower fuel pump pressure. Therefore would a larger diameter hose be needed to get the necessary LPH to a carburettor, when there is less pressure to push the fuel?

With EFI there is more pressure to overcome flow restriction in the hose. Therefore a higher LPH?

Just wondering out loud, with no real world experience. Happy to be educated

Cheers,

Nige

[Rian_Colorado]

Crap! My setup is EFI, and I've been worried about this exact thing. (but I missed Pauls input!)

As Mike mentioned above, the PFTE line in a 6AN setup is definitely NOT close to "3/8". I measured the ID of mine at somewhere near the .31 range as well.
Motor Dyno'd at 575hp, so I'm concerned that this just isn't large enough. With the pro-flow4 setup, it's running 58psi, and the pump is a 340LPH setup.

Wondering what you all think about me needing to go 8AN.....

Rian

[Jim1855]

In a past life I ran two different cars both plumbed with 3/8" steel line and a mechanical fuel pump. All was good with a carb'd 427 and 540 HP, often run to 7,000. Lots of dyno runs too, never an issue.

Friends had various big blocks (520 c.i. +) with far more HP than I had, still running steel 3/8 lines. No problems.

But then for the current Challenge Car and the same 427, I'm planning on AN-8 PTFE lined lines. Still a mechanical pump and the same regulator. Why? Simply because I can. I'll run AN-8 for the return.

I ran an Aeromotive Bypass Regulator after the carb. With today's low boiling point alcohol fuels the regulator allows the percolating fuel a place to go rather than past the needles. I've spent a fair amount of time alongside a road watching gas flow past the needles. Heat and altitude (low pressure) do not play well with the current gas. EFI does solve the problems, it's hard to boil 50psi gas.

BTW, I'm old and have no intention of switching to EFI.

Jim

[gbranham]

Crap! My setup is EFI, and I've been worried about this exact thing. (but I missed Pauls input!)

As Mike mentioned above, the PFTE line in a 6AN setup is definitely NOT close to "3/8". I measured the ID of mine at somewhere near the .31 range as well.
Motor Dyno'd at 575hp, so I'm concerned that this just isn't large enough. With the pro-flow4 setup, it's running 58psi, and the pump is a 340LPH setup.

Wondering what you all think about me needing to go 8AN.....

Rian

Do you have any symptoms that make you doubt your current fuel delivery? For what it's worth, I'm running a 427 with ProFlo4 and the GSS340 255LPH pump with all Evil Energy braided PTFE and 6AN fittings. The PTFE has an ID of 5/16". And I'm around 500hp. My car runs great, easily maintains 58PSI, and the AFR is right where it should be. Pulls hard up to redline, regardless of how much loud pedal I give it. Some would say my fuel delivery is undersized. I would disagree.

Greg

[Rian_Colorado]

Thanks for the input Greg, I think our setups are nearly identical - so it's good to hear that you've not had any issues whatsoever.
I only have about 1 mile on the car at this point - so no real symptoms or issues yet. It would certainly be easier to change now that later though! That being said, I think I'll leave it alone based on others experiences....

[cv2065]

You have to be careful when sizing as not all -6 or -8 lines are the same. Tube is measured on the OD so -6 or 3/8" fuel line tube @ 0.028" WT will have an ID of 0.319". -8 will be 0.44" ID

However, in theory -6 AN hose should be somewhere around 3/8" ID but they're not all the same and when you add Teflon liners like you should for today's ethanol blended fuels it can be considerably less than 3/8" ID. I have three or four different brands of -6 PTFE lined hose in my garage and they vary widely in ID size.

Anything more than 450 HP or so just go with -8 and don't worry about it.

This is a great point Mike. I found that out the hard way which is why they say don’t mix and match fittings and hose from different manufacturers.

[edwardb]

Crap! My setup is EFI, and I've been worried about this exact thing. (but I missed Pauls input!)

As Mike mentioned above, the PFTE line in a 6AN setup is definitely NOT close to "3/8". I measured the ID of mine at somewhere near the .31 range as well.
Motor Dyno'd at 575hp, so I'm concerned that this just isn't large enough. With the pro-flow4 setup, it's running 58psi, and the pump is a 340LPH setup.

Wondering what you all think about me needing to go 8AN.....

Rian

Mainly, what I said before deleting the non-responsive content, was that my current build with a 580HP Aluminator is using a Holley 340lph in-tank pump. Per Holley, "The module has been designed with a 340 LPH (liters per hour) Sniper fuel pump that will support up to 700 EFI or 900 Carbureted horsepower (HP Rating @ 60 PSI at 13.5 Volts / 16.9 AMP Draw) The flange has a 6AN o-ring outlet and return port." Since it has 6AN fittings, makes sense that the rest of the system can be plumbed with 6AN. I'm confident it will be fine. Yours should be too. On a side note, agree that ID of AN hoses can vary, that's why I also don't recommend mixing brands of hose and connectors. I've used Aeroquip on my last few builds.

[danmas]

I have supposedly a 550hp setup with a terminator x and inglese efi system running 6AN and a 255lph in tank system. Will probably do a dyno pull at some point and I haven’t drive it much. That said, the good news is I could run new 8AN if I had to pretty easily but I think I will be ok as well.

[Mike.Bray]

The flange has a 6AN o-ring outlet and return port."

I'm in the planning stages of my 427/ProFlo4 installation in my Camaro and have been looking at this exact thing. I ran all -6 lines on my Cobra but the majority of the runs are hard line. The Camaro will be all flex lines so the smaller ID hose vs. hard line gives me concern not only with capacity but also friction putting more load on the pump. So I'm going with -8 and using these adapters on the fuel pump. https://www.holley.com/products/plumbing_an_fittings_and_hose/adapters/an_to_an_adapters/an_o-ring_port_to_flare/parts/AT985086ERL

[Bart Carter]

FWIW
A 255 lph pump at 0.5 BSFC, 80% duty cycle and 20% safety factor will support 700 HP.

According to Aeromotive, a 3/8 (-6 AN) line to and return (EFI) will support 675 HP with a 255 lph pump.
Note that you should plan smooth bends and no bottlenecks as much as possible.

From a Holley installation manual, a 3/8” diameter line (-6 AN) line is adequate for engines to at least 750 HP. This is a conservative number

[Cobraman]

Got it, I'm running full length an6 line to and from with evil energy fuel filter small sweeping curve from under passenger footbox up to pressure regulator in engine bay no fittings. I'm glad I'm on the right track. Thanks