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  1. #1
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    Default Confused - Educate me on fuel line sizing

    Haven't posted in a while but I'm still plugging away on my long-term project.

    I've got my engine built and dyno'ed with a carb at 514hp at 6200 rpm (crank) and am working on the fuel system for EFI. Several years ago I bought a bunch of -6AN fittings, fuel filters (100 and 10 micron), Walbro fuel pump (http://walbrofuelpumps.com/walbro-gsl392-inline-fuel-255lph-pump.html), -6AN tube nuts and sleeves for 3/8" OD (1/4" ID!) aluminum line, etc, etc. All of the stuff is basically -6AN or fits to -6AN. At the time I was thinking I'd be around 375-ish HP crank. Had a little scope creep in the HP department. Anyway, I'm reviewing in light of that.


    • I've got 42lb injectors which should easily support the power (I'm hoping to be almost 550 NA crank HP on premium) when this is all done but hopefully not too overkilled.
    • The pump supports 670hp according to Walbro's website.
    • From what I've read.-6AN supports right around 600hp at the pressure I'm looking at.
    • The 3/8" OD, 1/4" ID aluminum hardline, to mate up to the -6AN, from what I've read will NOT support that much HP but when I look at the inlet on the Walbro pump at only ~3/16" (!) ID after the fitting is screwed in, I wonder how it can be possible that this pump supports 670HP?


    What am I missing and what would you recommend I do?

    Thx!

  2. #2
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    The first thing I would do if I were you would be to decide which EFI you want. Because you currently have a carb manifold, the current preferred setup is the FiTech 600hp throttle body EFI setup. Then once you have that decided you can look at the installation instructions of the recommended fuel system. That said, -6AN (3/8") will be just fine for your hp level but if you run an external pump you will need -8AN on the supply side of the pump or better yet install an internal fuel pump tank.
    Steve Hayes
    "Dust Off"
    68 Camaro

    Speed has never killed anyone. Suddenly becoming stationary, that's what gets you!
    "Jeremy Clarkson"

  3. #3
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    Quote Originally Posted by TheJDMan View Post
    The first thing I would do if I were you would be to decide which EFI you want.
    Thanks for your reply. The intake and carb were supplied by the engine builder just for the purposes of the dyno test because I wasn't ready with the EFI stuff yet. I already have a Offy Boss 302 tunnel ram base with port injector bungs added. I have Fuel Safe fuel cell so would prefer to run an external pump.

  4. #4
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    OK, well if you're running an external pump I can tell you how I set up my fuel system. I'm running an Aeromotive A750 external pump which is mounted directly in front of the tank. I was instructed to run -8AN (1/2") from the tank to the supply side of the pump and also to instal the 100micron filter on the supply side of the pump. I installed the 10micron filter on the pressure side of the pump and from there the rest of the fuel system is all -6AN. The pressure line runs from the pump to the EFI's fuel rail and back out where the pressure regulator is installed and after the regulator it becomes the return line back to the tank.

    Edit: I just remembered I took a picture of the pump setup a while back. The 100micron filter, pump, 10micron filter are the red canisters all of which are mounted on the aluminum plate with -8AN line from the tank to the 100micron filter and -6AN from the 10micron filter on. The two blue canisters are the shock remote canisters and not part of the fuel system.

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    Steve Hayes
    "Dust Off"
    68 Camaro

    Speed has never killed anyone. Suddenly becoming stationary, that's what gets you!
    "Jeremy Clarkson"

  5. #5
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    Thanks. This helps. Your setup looks remarkably similar to mine except mine is black and silver. What are the details of your engine and where are you at for power?

  6. #6
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    1st gen SBC with a MSD Atomic throttle body EFI stroked to 385 right at 530hp.
    Steve Hayes
    "Dust Off"
    68 Camaro

    Speed has never killed anyone. Suddenly becoming stationary, that's what gets you!
    "Jeremy Clarkson"

  7. #7
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    Steve - VERY clean looking setup. Is the mounting plate solidly attached to the car? I'm just wondering how loud a external setup like this is.
    chunger

    '68 Ranchero 500
    '70 Cougar XR-7 Convertible
    '98 Mustang GT Convertible

  8. #8
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    Steve: Similar power levels - this is a good comparison.
    Last question. What ID line do have going up to your engine compartment?

    Thx again

    Shawn

  9. #9
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    I have the 600 HP FiTech EFI on my '68 Camaro. When I decided to make the change I called FiTech and asked their recommendations, a 3/8" inlet and return was their response. Really liking the EFI by the way.

    Carl Wilson
    1968 Camaro - T-56 6 speed - 383 Stroker, 2014 Mustang GT seats

  10. #10
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    Quote Originally Posted by feeble View Post
    Steve: Similar power levels - this is a good comparison.
    Last question. What ID line do have going up to your engine compartment?

    Thx again

    Shawn
    Everything on the pressure and return side of the fuel system is -6AN (3/8). The short bit from the fuel pickup to the input side of the pump, about 18", is -8AN (1/2).
    Steve Hayes
    "Dust Off"
    68 Camaro

    Speed has never killed anyone. Suddenly becoming stationary, that's what gets you!
    "Jeremy Clarkson"

  11. #11
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    I’m switching over to -8an and 1/2” hardlines. Some extra power, dual zl1 pumps, and e85 is being installed. After I enjoy all of that it will be boost time

  12. #12
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    Quote Originally Posted by icemanrd19 View Post
    I’m switching over to -8an and 1/2” hardlines. Some extra power, dual zl1 pumps, and e85 is being installed. After I enjoy all of that it will be boost time
    What is the best way to do hard lines? Ni-Cu best?

  13. #13
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    I am using the Ni-Cu for my lines right now and find them to be great. They bend with ease, flare (AN 37) perfectly, have the strength needed and look great. The only potential down side would be if you use them with E85 they might be effected over time.

    Thats my 2
    1969 Camaro

  14. #14
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    Quote Originally Posted by Motobrewmaster View Post
    I am using the Ni-Cu for my lines right now and find them to be great. They bend with ease, flare (AN 37) perfectly, have the strength needed and look great. The only potential down side would be if you use them with E85 they might be effected over time.

    Thats my 2
    What tool(s) you using to bend them? I have seen two ways to terminate the line to make an AN connection; first is the tube sleeve with a AN flare to make a female connection, which is what it seems you are doing, and the second uses a ferrule and terminates in a male AN connection. I use Swagelok at work and don't see an issue with the ferrule and I have had headaches in the past with AN flares on Aluminum. Any reason not to do the ferrule and the male AN connection?

  15. #15
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    As far as line sizing, if I am running EFI at 50+psi can I run a 1/2" supply and a 3/8" return? Do they both have to be 1/2"? I am looking at 550-600hp and want to run E-85. I have an Aeromotive in tank A1000 pump.

  16. #16
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    I bought a 1/2" stainless steel line from inline tubes. Now the thing with stainless steel is that you MUST cut it with a 32 tooth hacksaw. DO NOT USE a tube cutter or cut off wheel. It will harden the metal and when you try to flare it the flare will crack in 2 or 3 spots. Buddy is using aluminum 1/2" line but i "heard" its not ideal with e85.

  17. #17
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    From a line size standpoint, high-pressure AN6 can support quite a bit of power. As a test, fuel pressure sensors were placed just after the outlet of a GM ZL1 fuel module and in the fuel rail. Each sensor was calibrated and fed from the same power source. The engine is in the 625FWHP supercharged range. Between the aft and rail sensor there are nine fitting connections including a forged 90 on the fuel rail.

    AT WOT the pressure delta is 2.3psi.

    So what does that mean?

    The % change in AFR due to fuel pressure delta is the square root of the delta. So, a 4psi change = SQRT(4psi) = 2% AFR change.

    For an engine targeting 13.5:1 AFR, a 2% change makes it about 13.75:1. It's not much, and easily compensated for in the tune. The OEM's have very much the same line losses.

    There's no drawback to going bigger, but the cost and trouble are often just not worth it.

    For going big (dual ZL1, CTS-V, etc.) going AN6 ==> "Y" ==> single AN8 to the engine makes sense. E85 is a 30% increase in required flowrate so everything often needs to get bigger.
    VaporWorx. We Give You Gas http://www.vaporworx.com

  18. #18
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    Quote Originally Posted by CarlC View Post
    E85 is a 30% increase in required flowrate so everything often needs to get bigger.
    Yes, that is my hang up... it will probably be OK. Part of the issue is that I want to put the flex fuel sensor in the return just before the tank, and all the ones I have seen are 3/8" line. I am thinking doing -8 from the tank to a Y, -6 on the two outlets from the Y that feed the left and right rails, -6 on both lines downstream that connect into the regulator, -6 out from the regulator back to the tank. I will probably only really run about E20 mix anyway...

  19. #19
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    What do you know

    Serious gents if you want the best advice reach out to Carl. He set me up with the electronics to run my dual zl1 setup on e85



    Quote Originally Posted by CarlC View Post
    From a line size standpoint, high-pressure AN6 can support quite a bit of power. As a test, fuel pressure sensors were placed just after the outlet of a GM ZL1 fuel module and in the fuel rail. Each sensor was calibrated and fed from the same power source. The engine is in the 625FWHP supercharged range. Between the aft and rail sensor there are nine fitting connections including a forged 90 on the fuel rail.

    AT WOT the pressure delta is 2.3psi.

    So what does that mean?

    The % change in AFR due to fuel pressure delta is the square root of the delta. So, a 4psi change = SQRT(4psi) = 2% AFR change.

    For an engine targeting 13.5:1 AFR, a 2% change makes it about 13.75:1. It's not much, and easily compensated for in the tune. The OEM's have very much the same line losses.

    There's no drawback to going bigger, but the cost and trouble are often just not worth it.

    For going big (dual ZL1, CTS-V, etc.) going AN6 ==> "Y" ==> single AN8 to the engine makes sense. E85 is a 30% increase in required flowrate so everything often needs to get bigger.

  20. #20
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    Quote Originally Posted by icemanrd19 View Post
    What do you know
    Lol! Don't ask my wife that question. Fortunately, I married way up in the smarts department.

    VaporWorx. We Give You Gas http://www.vaporworx.com




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