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· Junior Charter Member
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Discussion Starter · #1 ·
I am going to run a 347 with a carb and mechanical fuel pump. I should be pushing close to 500hp. Mostly street, some auto-x and a rare track day. So I won't be at 6000 rpm all day.

After quite a bit of reading, I decided to change out my hard lines from 5/16 to 3/8. I am not planning on changing the tank pickup (5/16) unless I have an issue. Many things that I have read support this. A lot say just to change the hard lines and that is good enough because you are enlarging the long line (laminar flow issues) with the most sharp bends. This cost me about $20.

I was thinking about going 3/8 hard line all the way to the pickup. With a canister filter (3/8 in / out), and fittings, adapters and more fittings it is getting pretty expensive to go about two feet. About $100. I know $100 is not much in the big scheme of things. But is it $100 that I need to spend?
 

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Personally, I would go with the 3/8. Overkill on the fuel system is never a bad thing, and it will be easier to change before the car is finished. At WOT you don't want to run out of gas.

Don H
 

· FFCobra Fanatic
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The fancy fittings arent necessary in such a low pressure application. They do become more important with the 50-60psi seen with EFI. All the AN fittings and stainless braided line are really more for looks than function. I have a 331 that I would expect to be in the 375hp range and I ran 3/8" line to the front and then rubber up to the carb. I dont expect tohave any issues with my setup. Like I said, all the fancy fittings are just for looks. If that doesnt matter to you, I would spend a little extra on a nice pickup for the tank and keep the rest simple. Good Luck with it!

Mike
 

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Avalanche 325 , Please help me out ,for years I have been thinking and telling others that my 347 is around 400 HP . I have a balanced rotating assembly aluminum heads, Deck and lined bored block ,a MSD 6al w/billet distributor from MSD, Air Gap intake 780 Holley and Ford X cam and four into four headers,,do I have 3 , 4, or 500 HP could you advise me, Please..
 

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Hmmm I don't think it is that easy to calc HP from a list of parts, it is important that they complement them in the right way. Only real way I know to calc hp---DYNO????? I'm just a novice at this
 

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I would run 3/8 hard the length of the car and spend some money on the pickup. At the engine compartment, convert over to soft line (braided if you want the looks) and run your filter off the soft line. Plumbing hard line straight into the filter or pump looks really nice but it can be a pain in the backside when you need to service the filter.

If this is a street car, avoid the aluminum line and go steel, preferably stainless. It's more expensive but less likely to be damaged by any kind of debris or abrasion.
 

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I'm running 3/8" hardline on my 331 with dual quads
 

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I'm running 3/8 stainless hardline in my 347 powered Mk4 this weekend. I'm lucky... live pretty close to Inline Tube, so picking up my 3/8 fuel and 3/16 brake line in person. I can fit 11+ long pieces in our SUV, so will have nice straight lines to work with.
 

· Junior Charter Member
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Discussion Starter · #9 ·
You guys just love spending my money!!!

I am going to go with a canister type filter in the stock FFR location. It can be hard-lined because it has a replacable element. There is a screw off cap.

I used 3/8" steel for the main run. This will take me hard lined from the pick-up all the way to the engine bay.

I will put a flex line from frame to pump.

I will probably go stainless (for the shine factor) from pump to carb. If you haven't noticed, I am not a big fan of flex hose for fuel. Especially after doing some reading here about leaks.
 

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I have 3/8 line on my 428 with duel carbs (around 430 HP) and I don’t run out of fuel at WOT. Good advice as said before, use the stainless lines for a road car. Many don’t and have no trouble, but I just don’t like chancing it since the stainless seems to be tougher and last longer in certain conditions.

The thing about the filter in the soft line can be a big DO thing if you don’t like fighting the filter for servicing. The hard lines can get a bit frustrating some times.
 

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Some thoughts:

- 3/8" should be plenty big enough.

- All the line before the mechanical fuel pump will be under suction, not pressure. If one of the lines leaks under use, it will suck air instead of fuel into the carb.

- You don't need to use AN fittings for the hard lines. Brass works just as well, and is a bit cheaper.

- Like you, I don't like rubber hoses and clamps. I like AN lines and fittings.

- That being said, in your application a rubber fuel line will easily last a decade or more. Look at an old Mustang, how long has that rubber line been hanging off the front of the fuel tank? 20 years? 30?

- I'm not a big fan of stainless fuel lines. They can be very difficult to work with, don't always flare well, and are definatly expensive. Again, look at an old Mustang. How long do you need your fuel lines to last? At 3,000 miles of good weather driving a year, I would expect steel lines to last a few decades.
 

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Discussion Starter · #13 ·
Avalanche 325 , Please help me out ,for years I have been thinking and telling others that my 347 is around 400 HP . I have a balanced rotating assembly aluminum heads, Deck and lined bored block ,a MSD 6al w/billet distributor from MSD, Air Gap intake 780 Holley and Ford X cam and four into four headers,,do I have 3 , 4, or 500 HP could you advise me, Please..
It would be really hard to say. There are some "desktop dyno" programs that you plug everything into and it would give you a ballpark estimate. What heads you have will make a big differance. There are AL heads that aren't much better than stock and some that will really get the power up. Pistons, intake, everthing makes a difference.

Even if you put your car on a dyno, it all depends on the calibration. The "tuner" crowd will avoid the guys whos dynos give low numbers and go to the guy with the high calibration.

Around 400 at the wheels is pretty common for a 347 though.
 

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Hi Avalanche,
I know this is a plumbing fact: The size of the system is limited by the smallest fitting or line used. So if you have a 5/16" pickup, your system will never flow more than the limiting 5/16" line.
Please remember these lines are all measured in outside diameter. A 3/8" (.375") line has a .300 inside diameter. A 5/16" line (.3125") has a .220" ID.... Brands of tubing do vary.....
 

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I did 3/8" hardline the full length with a sintered bronze canister filter near the carb. The only flex line is from the pick-up to the hard line, from the hard line to the mechanical fuel pump, and from the hardline that comes out of the pump to the distribution tube at the carb. I made the whole run myself using a roll of stainless tubing from McMaster Carr and it wasn't very expensive.
 

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Hi Avalanche,
I know this is a plumbing fact: The size of the system is limited by the smallest fitting or line used. So if you have a 5/16" pickup, your system will never flow more than the limiting 5/16" line.
Please remember these lines are all measured in outside diameter. A 3/8" (.375") line has a .300 inside diameter. A 5/16" line (.3125") has a .220" ID.... Brands of tubing do vary.....
Isn't flow restriction a function of length and diameter. For example 1 ft of 5/16" line doesn't have nearly the resistance to flow as 30 ft of 5/16" line. That was my understanding. Been awhile since I studied fluid dynamics. Wall effects and boundary layers and all that stuff... those equations can give you nightmares.

But 20 ft of 3/8" line may actually be much more restrictive than the 2 ft of 5/16" line. Obviously removing the 5/16" line is better, but may not actually significantly improve total flow through the system.

Another question, is hard line measured differently that flexible braided line? Isn't 3/8" braided line 3/8" ID?
 

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I did 3/8" hardline the full length with a sintered bronze canister filter near the carb. The only flex line is from the pick-up to the hard line, from the hard line to the mechanical fuel pump, and from the hardline that comes out of the pump to the distribution tube at the carb. I made the whole run myself using a roll of stainless tubing from McMaster Carr and it wasn't very expensive.
x2 did the same thing pretty much
 
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