Got to say thanks to Barry R about 3/8ths fuel lines on CJ cars"

[Qikbbstang]

In the thred below about Running out of gas Barry R stated:.
"I would not mess with jetting until you've got the 3/8 line installed along with the better pump.
There's a reason Ford did that on stone stock CJ cars in the 60s - its necessary."


BINGO anyone that has a Ford Mustang unibody or I presume other model unibodies that had an optional CJ available can simply buy the replacement/reproduction 3/8ths fuel line assembly from NPD or any other high-end collector car parts houses then you don't have to fab a fuel line  ........Cool!

[bartlett]

any links to this ? Im interested ../// Is there a sender that is bigger also ?

[ScotiaFE]

http://www.autokrafters.com/p-4115-fuel-sender-66-69-flcm-38-inch-pipe.aspx

[Qikbbstang]

http://www.npdlink.com/store/products/fuel_line_tank_to_pump-106964-0.html

[My427stang]

BB, as a guy who deals in differential pressures and flow loss, how about either doing the math to compare a 5/16, 3/8 and 1/2 line with a mechanical pump or finding someone who can? 

I am not being a wise-ass, I'd truly like to find out.  The issue really that comes into play that I am not sure how much negative pressure on pickup side is lost over 10 feet of 3/8 versus 10 feet of 5/16 and how all the things that affect pressure loss in a pipe converts to suction and flow.

Although I agree that a 3/8 line is good insurance, or even bigger (I run 1/2 inch on my Mustang), but in my opinion, not until 500 hp do you really task the ability of a 5/16 line if you have an adequate pump.  May not seem like it, but by converting a known HP into BSFCs ranging from .5-.6 into lbs/hr and that into GPH, assuming no kinds kinks, restrictions, or other baloney, would make you think that a 5/16 line with a good pump should feed more than most street/strip motors would need

Need to remember that the cars of the 60s used the fuel pumps of the 60s. 

I'd also add that anyone who changes line size and pickup size, take a good look at the adapters and inverted flare seats in most pumps, rarely will you see them the same size of the line.

Now with that being said, there sure isn't any reason NOT to run a bigger fuel line, but the 400 hp motor that we were talking about had a vent problem, you could go 1/2 line and not that make his car run better.  In addition, I'd expect most CJs of the day did too, as a Mustang tank uses a crappy vent setup, basically a "dent in the gas cap sealing surface" to vent the tank.

I used some basic pressure drop calculations on the pressure side and backed it into flow loss after the pump and it can surely feed even a stroker, but the pickup side of a pump is MUCH less negative pressure and is dealing with a longer line.  There has to be a way to calculate, but I don't know how, are you able to?

[machoneman]

http://www.lmengines.com/fuel_lines

Click on the fuel line size calculator in this link.

[My427stang]

That's a decent calculator for a pressure side, but I am not sure what it is telling me in terms of a mechanical pump pulling, vice pressure building on the output side.

If 10 feet of 5/16 creates 2.9 PSI off loss, there isn't 3 lbs of vacuum on the suction side.   

I will say it is almost a full 1.0 PSI of pressure loss comparing a 3/8 to 5/16 due to friction, that seems to be very significant.

I am not sure you can say a 3/8 is 33% easier to PULL fuel from the tank at the given vacuum of the fuel pump, but if that is true, it's significant

[Qikbbstang]

 Here's a part of line sizes that really stumps me.  Put aside the pipe flow restrictions and think about the weight of the volume of fuel within the fuel line. Most of "use" our motors to accelerate: when you dump the clutch that column of fuel from the tank to the carb resists accelerating. If it is in a 1/4" line the forces are but a fraction of that upon a 3/8ths or 1/2" line, don't forget to factor in the length of fuel line from tank to pump is 15-20 feet making it a column of fuel.  I know a standing 15-20 ft column of water exerts literally pounds of pressure and theoretically under something like 1-G acceleration or some fraction thereof the fuel line resembles a standing column of water.
When you have the same given mechanical fuel pump trying to pull/suck the fuel that wants to stay put through the lines to me there has to be more resistance/force in the larger lines that hold more fuel then the small lines under hard acceleration. I guess it all comes down to how much force can be exerted by the "G" force  on a 1/4", 3/8ths and 1/2" column/volume of fuel but I'm sure there is a whole lot more involved?   
Honestly like many other oddball things in auto engines it's surprising things work as well as they do.  It just seems amazing that mechanical fuel pumps work as well as they do. No doubt the tank mounted electric fuel pump used in drag racing is key but then again there are many "street" cars that manage to "run" with only a mechanical fuel pump. 

[jayb]

BB, I don't think that the G forces on the fuel in the line are all that significant.  Let's say we have a 1/2" ID fuel line that is 15 feet long filled with fuel.  The total volume in the fuel line in cubic inches is 0.5 X 0.5 X 3.14 X 15 X 12, or 141 cubic inches.  There are 231 cubic inches in a gallon, and a gallon of fuel weighs about 6.5 pounds.  So, the weight of the fuel in the line is 141/231 X 6.5, or about four pounds.  If you accelerate at 1g (which most of us don't), then the force on the fuel at the tank end of the line will be 4 pounds, and the force on the fuel at the pump will be essentially zero.  For a 3/8 or 1/4 inch line, the force will be significantly less.

Not saying that this isn't a drag on the pump, but I don't think that part of the equation is a really big deal...

[chris401]

Adding to checking ID on filters and fitting I to had to enlarge filter and fittings and the four cross holes on each end of filter. My 401 was needing fuel after about 5200rpm. Problem corrected after updating to the 3/8. My 5/16 lines were probably more build up than size issue but it worked. The first issue was the LMC gas tank. The flare was much smaller id than the 5/16. I had a local shop up grade tank to 7/16.

[Qikbbstang]

a mechanical pump must face. Of course the pump being a diaphragm is creating a vacuum to pull the fuel through the line and then take the fuel and pressurize it up to the carb.  I admit I have a tough time comprehending how a diaphragm pump performs when faced with a vacuum. 
I find interesting your "calculating the weight of the fuel in the line is 141/231 X 6.5, or about four pounds.  If you accelerate at 1g (which most of us don't), then the force on the fuel at the tank end of the line will be 4 pounds, and the force on the fuel at the pump will be essentially zero." I've always had a tough time on intangibles and for me the vacuum to PSI as discussed here is tough to grasp. If the vacuum created by your example is zero then it seems to me the typical auto's diaphragm pump would be playing hell to work sucking against that vacuum and then building pressure. I guess this all means that if you have a reasonably quick car then an auxiliary elec  pump at the tank is a mandatory.  If you drive a moderate performer  as the creator of this thread I'd certainly think that things could get wacky fast. Especially since your pulling a vacuum on todays fuels that boil so easily (vapor lock) Just the time you don't need it is the worst - when you are pulling hard.  The Classic Dragsters with fuel tanks mounted in front of the car may have been good for one thing that 6lbs pressure was feeding the pump LOL.

[MT63AFX]

In the time period BCJ (before Cobra Jets), Ford's 3/8" fuel line would adequately feed a stock 2x4 427 spinning to 7,000rpm, without a hiccup, using a mechanical fuel pump that the Ford engineers deemed sufficient enough (i.e. engineered) to accomplish their goal of having one badass engine that didn't need to be reengineered or use aftermarket parts (which were few and far between for the FE in the BCJ-world). Ford did quite well at Daytona in 63 didn't they? JMO, Rod. BTW, to stick a 352-390 2v fuel pump on an FE and expect it to reach 6,000rpms is iffy at best,  .

[JimNolan]

Guys,
    The car My427stang and Barry R. was talking about was mine. I now have a 3/8" fuel line from the Edelbrock high volume pump that is covered by a 3/8" fire sleeve. ( I used it on my airplane fuel lines to hold the cold of the gas in while insulating the line from heat ). I have a 3/8" fuel line to the tank but I still have the 5/16" welded fitting at the gas tank. As My427stang stated, my vent line from the gas tank was clogged up completely. I couldn't even blow 100 lbs of air through it. It's clear now. 
    I ran the car at Bunker Hill last weekend and it seemed to actually impress me more than at the Meltdown Drags. I was 0.7 sec quicker in the 1/8th mile at Bunker Hill. But, I also increased initial two degrees and bumped total to 38 degrees. 16/38
    The only reason I was hesitant about the 3/8" line was the fact that the 300hp engine with a 570cfm carb did the same thing two years ago. I tend to believe My427stang was right about the vent line. If I have trouble with it again the 5/16" fitting at the gas tank will get changed to 3/8". I'll repost after the Ford Expo this Labor Day. 

[Cyclone03]

I missed the chance to reply to your first post, glad you got it figured out. I would like to add something though.

I have a 68 Mustang with a 430ci FE running RobbMc's big mechanical pump. RM suggest running 1/2" line on the inlet side so I did mine in Stainless hard line,except for a short piece of braided to my custom 1/2" pick up.

I had a problem I thought was heat related that when the weather was hot,May-Oct here,if the car idled for more than a one light cycle,2 minutes or so,when I took off the carb would flood. In my testing I only witnessed the fountain one time with the air cleaner off in the garage. Holly Heck the fuel shot out of the vents about 8"!
I don't know how it didn't catch fire!
I tried all kinds of heat spacers,wraps,fuel lines but couldn't fix it,and never ran it without an aircleaner. But what I didn't do was replace the one short piece of braided hose out back. The first summer I just lived with it.
Fast forward about Jan the next year and my wife commented on the "gas smell" in the garage. Can you do something about it? Well I read on line about older steal braid hose sort of "leaking" and the test was to sniff it. So when nobody was looking I put nose to hose so to speak. The short piece of hose smelled like an open gas can! It was not wet at all. I replaced that hose and the garage smell drop noticeably,and I still have a open tank vent with a small K&N filter on it.
That hose also added air to the suction side of my mechanical pump,so like a carb has emulsion chambers to add air, my fuel line did too! So I had a nice frothy mixture feeding the pump just when the floats dropped and the needles opened as I went across the intersections on the green light.

I think you fixed your problem by eliminating a vacuum leak in your fuel line.     

Hopefully I'm not crossing up posts here.

[cammerfe]

I use nothing but Teflon/SS braid. If you shop at a hose distributor there's no problem getting the larger sizes. No rubber to degrade.

KS