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Senior Contributor
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Fuel line delivery

How much difference does a fuel line make? Do you have to change the whole line or just the line in front of the pump to the carbs or just the line behind the pump from the tank? What about the stock metal bit from the above the fuel pump to over/around the engine. If the line is changed should it be discarded?

What line size is correct 5/15 or 3/8th?

thanks
 

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My personal opinion on a fuel line is based on a hydraulic application, basically because that's what's involved, liquid under pressure. Next, what is the application? low volumn/low pressure, or high volumn/high pressure, or somewhere in between. If it's a carb engine, low volumn/low pressure. An FI engine, depending on the fuel rail pressure regulator it could be high pressure/ medium volumn. Flow will be dictated by the restrictions in the delivery line. The pressure will be nominally the same anywhere in the line but volumn could be restricted. In my V-6 mod, I'll be using the largest line I can get using existing fittings. The fuel pump bypasses at 70 psig, the fuel rail bypasses at 50 psig. I don't know the rate of flow, but I believe I'll have more than enough flow for the 6 injectors at wide open throttle. In my estimation, more is definately better.

Ron
 

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I replaced all the lines from the tank to the carb with 3/8" lines. I used a high flow electric pump(carter p4070) with 3/8" fittings. I was able to remove the fitting from the tank with the tank still in the car and tapped the tank for a 1/4"(I think) npt fitting. It's the one closest in size to the original. I did NOT drill the old threads out as this would have required removal of the tank and flushing to ensure ALL gas and fumes were removed. It will now flow lots of gas as I verified when running gas through the tank to flush out and remove all rust. I probably ran 40 gallons through the system before the rust was gone...

Also, I don't use the metal line and don't run the lines over the motor. I always use rubber lines and run them in front of the radiator. That change alone made the difference between a VERY painfull experience changing the main jets on a DGAS to a mildly warm experience...

-Travis
 

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boomerang opeler
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5,634 Posts
flow and pressure depend on restrictions
if you are using the orig pump then it will only flow at 1 rate so theres no need to go above the orig bore (the output from the tank is a limit to this also)
if you uprate the pump then you can use a bigger bore but you will over pressure the float needle in the carb and flood the engine
if you feel you need the extra folw then put a return line to the tank or between the tank and pump so you do not pressurise the carb
if its for injection then you wil have to put the return line in anyway
 
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