how big of fuel line do i need

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abodyhotrod

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i have the stock fuel line that is the smaller of the two. i need to know if the 5/16th line can support a 750 cfm 360. also the fuel pump, should i go w/electronic fuel pump over my stock one.
 
If you just drive it around, the 5/16 line will feed it.

If you plan on running it hard, at least a 3/8 line is what you need. I know there are bunches of people that will argue you don't need 3/8 line or bigger. I've had cars that we thought ran pretty good, replaced the 5/16 with 3/8 line and the car picked up .15 and MPH with only a line size change. That's 3/8 from the sending unit, to the carb.

Fuel supply line size is one of the most overlooked component on cars.
 
If your motor has stock internals you will be fine with the 5/16". But if your motor is not stock inside and you use a mechanical pump you may need the 3/8" line. If you use an electric pump and put it back by the tank then you can most likely get by with the 5/16" line because it is easier to push a liquid than it is to draw one.


Chuck
 
motor has cam 480/480 lunatti, headers,high rise,3800 stall,4.11s.. i do have a fuel pressure gauge that reads 6 at idle, but seems to drop when it gets hot. i know my car is alot faster than a 15.4. i'd be happy w/a 14.2.
 
abodyhotrod said:
motor has cam 480/480 lunatti, headers,high rise,3800 stall,4.11s.. i do have a fuel pressure gauge that reads 6 at idle, but seems to drop when it gets hot. i know my car is alot faster than a 15.4. i'd be happy w/a 14.2.
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It's more than just the fuel line! Back in 1970 my '69 340 Swinger with stock motor, and 3.23 open rear end ran 14.28 @ 98 mph at OCIR. Your car should be a lot quicker than that with your combo. Of course a 3/8 line will help but I'd look a lot deeper than just the fuel line size.
 
Anyone know what size fuel line a slant six car is vs. a V8 car? Also, when you go to a bigger diameter line, do you need to change the sender or can the larger line be plumbed through the stocker and into the tank?
 
DemonDave said:
Anyone know what size fuel line a slant six car is vs. a V8 car? Also, when you go to a bigger diameter line, do you need to change the sender or can the larger line be plumbed through the stocker and into the tank?
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Most all are 5/16 line and it is fine. It is really only long hard pulls like a long freeway pull in elevation, ar a drag car, circle track car with 400+ HP that this is an issue, but as Moper said an electric pump will step up a 5/16 to be O in most cases. U used to see many motor home with 413 wedges, and 427 tall blocks running 1/2" line, but they had 30-50 distances to pull the fuel from and multiple tanks too.

Anyway, yes if you go 3/8 there is a 3/8 sending unit to match. Most 340 cars and up all had 3/8 tube. But I have seen even a 383 cornet with a 5/16 line before.

Hope that helps some?

General rule: If in doubt, install a fuel pressure gauge, stick the car on a chasis dyno and nail at full load at 60MPH wheel speed to see if under a load for more than 1 minute the pressure starts to drop, or if you can safely rig the lines up drive with a buddy and have the fuel gauge mouted wher you can see it when you drive under a full load.
 
5/16" is all most will ever need. No need to go nutzzz with a 3/8 line front to back. My father runs his 67 Satellite pretty damn hard, its a Stroked out 440 big block running a 900CFM carb and he has never had a "fuel starvation" problem. I would not worry about it. Have fun and put the $$ elsewhere. :)
 
Glad to hear that I don't need to endure the expense and frustration of replacing the fuel lines on my /6 Demon when I do the 360 swap in the spring... my list of to-do's is long enough!
 
You will hear a lot of different opinions on this but here is what I learned long ago from some veteran drag racers.

A little too big is not as much of a a problem as a little too small.

The fact that the car doesn't die out and is not "starved" for fuel does not mean it would not run better and faster with more fuel.

For a race or serious street/strip car, start big at the tank and reduce the size at each choke point-the pump, filter, and regulator, etc. This allows the quickest recovery of pressure after a drop. I have -10 AN from the tank (pickup with a ½" tube from Year One) to the filter and elec. pump in my trunk, -8 AN from them to the regulator, and -6AN from the regulator to the carb. My fuel pressure is steady as a rock no matter what I do.

Mount the regulator somewhere where body vibration can not lift the ball off the seat and flood the carb. A carb plate is best.

Up front, run the main line up to the firewall and turn back toward the engine to feed the regulator because you want the inertia of acceleration feeding the regulator not starving it.

When I bought my car it was race only and the fuel system was silly overkill. It had 2 ½" lines from the tank to 2 electric pumps, then 2 ½" lines Y'd down to a single 7/8" (yes, seven eighths!) from there to the regulator, and 3/8 from the regulator to the carb.
 
I would agree with those who say get a guage first,it really is trial and error.My good friend ran a blown dual carb engine for years with a single electric pump and a 3/8 line and it didnt benefit at all from larger line/pumps ect.I stepped up my fuel system a little from stock in a 12.50 car and saw no difference,bought a guage and confirmed I didnt need it,it really depends on alot of things so its always best to check first.
 
Well my sons Dart still has the original 5/16 line on it and it's run 11.50's @ 116 with no problems at all. He uses the Holley red electric pump. I run 3/8 on mine as I changed it when I did all the work on my 63. Ron
 
i have run 12.17 at 108 mph with the stock 5/16 line and a stock fuel pump im the 360 in my dart, i run a 750 dp carb.. but if you are gonna upgrade you may as well go 1/2" . it won't cost anymore and you'll be big enough for upgrades down the line.
 
I run a holley black electric pump,3/8" sending unit and line on my '70 stroked duster,last thing i want is fuel starvation or a failed mechanical pump dumping fuel into my oil...
 
I have had hot street combos that would lean out with 5/16 and some that would not. Maybe some of the 30 year old lines are rusted on the inside. It is a good idea to replace the fuel line anyway so go with 3/8 alum line and rout it in the factory location. It very easy to do. I have drilled out the factory senders and added a 3/8 pickup to them. (alittle tricky) The aftermarket senders work great but are alittle more costly. The fuel pump should be changed to electric or a high flow holley or carter mechanical with 3/8 fittings. A factory pump has 5/16 fittings so upgrade here as well. I like the mechanical for street use due to saftey and noise issues. In cause of a wreck, a electric fuel pump will not shut off by itself unless an interia switch has been installed or the pump is run off of an oil pressure switch. Mechanical is much easier, jmo Ray
 
The way I see it:

If 5/16th can feed a HEMI 8bbl, then it's more than enough for any pump gas small block...

Also, stick with mechanical pump. There is no reason to convert from what you've said about your combo...
 
One thing to consider when selecting a fuel pump is how much time your going to spend on the street.When I ran an electric pump I always carried a good used spare just in case for the long cruises to the beach,but with a mecahnical you can get a replacement at any corner parts store.If Im starting from scratch Ive always ran a 3/8 line with an electric as a pusher so I know I have enough fuel-but I havent gotten that far with the duster yet.
 
I always run an electric pump and dont waste my time with a mechanical pump. Yes carry a spare if you feel better but my sons Dart has been on the road since 1997 and is still using the same red Holley pump. In hot weather you wont have to worry about vapor lock or fuel boiling with an electric and there is no way a mechanical pump will work as good as an electric pump and if you plan to race you need it that much more. Ron
 
I would like to add a question to this question.

I an electronic fuel pump is being added that requires a return line are the line to be of the same size?
 
KSP said:
I would like to add a question to this question.

I an electronic fuel pump is being added that requires a return line are the line to be of the same size?
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Ideally, the return line should be same diameter as the feed. I've seen systems that had a -10 feed and -8 return.
 
383man said:
I always run an electric pump and dont waste my time with a mechanical pump. Yes carry a spare if you feel better but my sons Dart has been on the road since 1997 and is still using the same red Holley pump. In hot weather you wont have to worry about vapor lock or fuel boiling with an electric and there is no way a mechanical pump will work as good as an electric pump and if you plan to race you need it that much more. Ron
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Ive had good success as well,but when your driving over one hundred miles one way through mountian passes its really nice to not have to place your fate in a cell phone that may or may not have service!,thankfully I never had it fail but you know murphys law.
 
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