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post #1 of (permalink) Old 03-09-2001, 02:05 PM
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Fuel Line Dia. - CJDave? - TR?

OK Brainiacs - here's a question. I figure you two are the most likely to have experience with this...

First of all, I am running a custom 26-gallon tank on my CJ-7 with one feed line, no vent lines of any kind, and a vented cap. This has worked well, but I do get vapor buildup in the Summer with a full tank, otherwise, it's fine...

Anyway, my feed line up to the engine is kind of rusty, old, and has a piece of rubber hose connecting to the tank and to the fuel filter (which is a firewall mounted marine unit that looks like an oil filter...)

ANYWAY, what I have in mind is to nix all of this and run stainless hard line with stainless Swagelok fittings for all of the fuel lines. However, all the stainless line and fittings that I have (and I have TONS) are 1/4" O.D. Is this going to cause a flow problem or maybe starve the pump? My brain says, "No" - that there are orifices at the carb fuel filter and needle and seat that are WAY smaller than this, so what's the difference? But my other half of my brain says, "It's the size it is for a reason..."

Can you help here? It's just a bone stock 360 with the MC 2-barrel, and it sure would be a much cleaner and tougher setup - I was planning on wrapping the entire line with rubber 1/4" I.D. fuel line as heat insulation and protection - pretty slick, huh?

Will it work? - Chuck

Chuck Hadley
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post #2 of (permalink) Old 03-09-2001, 04:12 PM
 
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Re: Fuel Line Dia. - CJDave? - TR?

3/8 would be more "standard" / ideal but I think 1/4 would suffice. What you'd have to look at is the flow rate of the fuel pump, not necessarily the psi rating of it. Then just figure out the volume of fuel that your 1/4 line can hold, and how long if would take your pump to "refresh" the fuel level in the line after the carb has taken a big gulp. I just think of it the way I would plumbing in a house. Older houses have smaller water lines and can still flow water pretty good, but require a higher psi to flow water at the same rate as a newer house with larger pipes. anyhow, just babling, good luck

[img]/wwwthreads_images/icons/cool.gif[/img] Big Ed
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post #3 of (permalink) Old 03-09-2001, 04:20 PM
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Re: Fuel Line Dia. - CJDave? - TR?

The feed line should be 3/8". I wouldn't wrap the steel in rubber either. Once the rubber gets hot, and it will, that heat will be transferred to the fuel anyhow and it will take longer to lose that heat. The bare steel line will do a better job of keeping cool with air flowing directly over it. This is why you hear fuel injection retrofits suggesting to use hard line wherever possible and as little rubber as possible.

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post #4 of (permalink) Old 03-09-2001, 04:38 PM
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Re: Fuel Line Dia. - CJDave? - TR?

Hmmm - Where are you guys getting the 3/8" figure from - like standard hot rods with Holleys and stuff? That's what I always used on those applications...

Anyway, the stock Jeep feed line is only 5/16"...

What about 3/8" with Brass Swagelock fittings and copper tubing? Would the copper pick up too much heat?

Chuck Hadley
post #5 of (permalink) Old 03-09-2001, 04:41 PM
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Re: Fuel Line Dia. - CJDave? - TR?

Hey-It all depends on what kind of horespower your running. If you have upto 100 horespower 1/4" would be fine; up to 200 horespower you could run 5/16" but depending on how much highway driving you do and the RPM's you run w/rear gear ratio go for the 3/8 diameter. Its always better to upgrade now than run into some other problems now even though your going to have that 1/4" laying around a little longer. You can use that on your lawn mower but it might be a little to big for your weed-wacker!...haha just kidding. As for the copper stay away!-its too weak of a meterial to have on a vehicle around knobby tire spinning little rocks at 3500 RPM. Even though a 'stock' jeep has 5/16" line how many guys do you know have stock jeeps anymore. Anytime you add power to an motor on any level you usually add more RPM's and a higher intake flow so you will need a larger fuel line...and an exhaust to let the motor breath.

MARK (OIIIIO) LANGMOTORSPORTS
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post #6 of (permalink) Old 03-09-2001, 05:19 PM
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Re: Fuel Line Dia. - CJDave? - TR?

I think it will work, probably not ideal, but it's free material, try it. Run thru the gears and hold it WFO until you get scared, If you let-up before it boggs, you're fine. I wouldn't sleeve it in rubber either.

post #7 of (permalink) Old 03-09-2001, 06:05 PM
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Re: Fuel Line Dia. - CJDave? - TR?

hey dirtrod.. youre just a mecca of techinical help arent you???? [img]/wwwthreads_images/icons/laugh.gif[/img]..
course.. that is the way i would tackle that problem also.. [img]/wwwthreads_images/icons/smile.gif[/img]

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post #8 of (permalink) Old 03-09-2001, 06:16 PM
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Re: Fuel Line Dia. - CJDave? - TR?

I'm not afraid do do a little R&D work, If I'm wrong, HE just has to redo it. : )

post #9 of (permalink) Old 03-10-2001, 02:11 AM
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Re: Fuel Line Dia. - CJDave? - TR?

Go with 3/8" for your application, you can never have too big of a fuel line. Here is my past experience...

5/16" fine for sixes and small STOCK V8's that aren't subject to alot of load or RPM (I havent had a stock vehicle yet that needed bigger).

3/8" Good for built sixes, mild small blocks, and STOCK to very mild big blocks. My 400" Dart had 3/8" 'till I broke into the 12's, then it needed 1/2"

1/2" for seriously built small/big blocks (race cars mud trucks etc.)

1/4" would only be sufficient as a return line...you do have a return line don't you. If not, the fuel heats up, starts to vaporize in the line, and the air pockets created have nowhere to go but into the carb, and an air/air ratio of 14:1 doesent do your motor any good.[img]/wwwthreads_images/icons/crazy.gif[/img]

Hope this helped.

Mike H.
1983 CJ-7 Laredo, It's a roller with drivetrain now!
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