5/16 nylon or 3/8 rubber fuel line?

[rockinrich]

If the fuel pump is mounted on the motor like a mechanical pump and carb then no. The whole assembly moves together.

The pump to fame mounted fuel lines need to flex since they move separately.

Items that move independently need to be able to flex. Electric fuel pumps the vibration can cause problems.

I apologize for not replying until now,but using rubber from the fuel pump to the carb wouldn't flex? I don't understand how it wouldn't.

 

[rockinrich]

Let me ask another question,if you were to just use nylon would you go with 5/16 or 3/8 and why?

 

[nvrstuk]

How many HP?
5/16" will work for anything close to stock.

 

[rockinrich]

How many HP?
5/16" will work for anything close to stock.

it's stock motor so not sure of horsepower.

 

[nvrstuk]

5/16" will flow more fuel you could ever use then. You'll be fine

 

[Speedrdr]

5/16" will flow more fuel you could ever use then. You'll be fine

Haven’t dyno run mine yet, but the builder estimated (with the stroker and heads…) that it should be around 450. Will the 5/16 flow enough for that?
Not sure if this is a thread “hijack”, but…

Randy

 

[DirtDonk]

It’s an almost-hijack. But more in the framework of adding more useful information.
With that smaller size your engine would run, but it would probably not be fully supported under heavier loads when using most of that horsepower.
Especially on a long hard pulls.

The larger 3/8” is pretty much the standard for motors of that power level.
Some even go bigger, but it’s not really necessary for 450 hp.
Unless you’re racing…

 

[rockinrich]

5/16" will flow more fuel you could ever use then. You'll be fine

sounds good! So like ford did it use nylon and then where you need to make bends just use the 3/8 rubber and in doing that i will need to get some 3/8 to 5/16 unions as well right?

 

[rockinrich]

Haven’t dyno run mine yet, but the builder estimated (with the stroker and heads…) that it should be around 450. Will the 5/16 flow enough for that?
Not sure if this is a thread “hijack”, but…

Randy

hijack all you want! All good info to hear!

 

[rockinrich]

It’s an almost-hijack. But more in the framework of adding more useful information.
With that smaller size your engine would run, but it would probably not be fully supported under heavier loads when using most of that horsepower.
Especially on a long hard pulls.

The larger 3/8” is pretty much the standard for motors of that power level.
Some even go bigger, but it’s not really necessary for 450 hp.
Unless you’re racing…

agree wholeheartedly paul regarding useful info!

 

[gnpenning]

I apologize for not replying until now,but using rubber from the fuel pump to the carb wouldn't flex? I don't understand how it wouldn't.

A rubber line will flex due to the fact it isn't ridged. So yes it will flex

On a carbureted motor with a solid line and mechanical pump they both are solid mounted to the motor and move in unison. Most of these types came from the factory with solid lines. Ford did use a short piece of rubber on the fuel filter instead of a flared fitting on both ends like some other manufacturers. The rest of the line was solid.

 

[Speedrdr]

It’s an almost-hijack. But more in the framework of adding more useful information.
With that smaller size your engine would run, but it would probably not be fully supported under heavier loads when using most of that horsepower.
Especially on a long hard pulls.

The larger 3/8” is pretty much the standard for motors of that power level.
Some even go bigger, but it’s not really necessary for 450 hp.
Unless you’re racing…

Thanks @DirtDonk for the affirmation that it wasn’t a complete thread jack. . I have zero plans to race, but I do want to “feed” the engine adequately. 3/8 line it is!

Randy

 

[nvrstuk]

Thread steal for sure. I thought I was answering for a stock engine. All good info, I just need to double/triple check who wrote what.

5/16" for stocker and 450 hp, even rear wheel 3/8" is plenty. More pressure makes a difference for EFI since 450 HP will need a custom tune anyway

I am assuming straight gas because ethanol takes a bunch more.

 

[lars]

For what it's worth, my 450+ HP 408 is plumbed with lines that have a 5/16" inside diameter. I have a fuel pressure gauge plumbed to the fuel rail, and a 40 psi fuel pressure regulator. At wide open throttle and 4500 rpm (at which point I'm zipping right along) the pressure is still right on 40 psi at the rail. If the system couldn't keep up it would be dropping.

 

[Speedrdr]

Thread steal for sure. I thought I was answering for a stock engine. All good info, I just need to double/triple check who wrote what.

5/16" for stocker and 450 hp, even rear wheel 3/8" is plenty. More pressure makes a difference for EFI since 450 HP will need a custom tune anyway

I am assuming straight gas because ethanol takes a bunch more.

Will probably be mixing some av gas as it ain’t liking straight pump gas.

Randy

 

[nvrstuk]

Yup, 100% agreed.

My concern is that it's common for people plumbing a line to not stay with that ID throughout was the reasoning for mentioning to the OP to go with 3/8".

Lars, your as bad as I am, no, maybe 3x worse since you work on airplanes! lol I'd be surprised if you didn't measure your fitting ID if they weren't all one manufacturer- I did.
I used calipers on every fitting making sure what were supposed to be the "same size" ones got sorted for their actual size and the others were returned.

I have a couple pipe thread fittings, AN fittings, high press EFI hose fittings- a variety - and was really surprised by thread size or fitting size differences compared to actual advertised ID.

 

[LHardin]

I'm not a mechanic and my only formal automotive education was one semester of High School Auto Shop in another lifetime; so what do I know? Anyway, here's my two cents.

Since a metal tube generally has a smoother/straighter finish inside where the liquid is, there is:
* Less friction loss from a smoother tube than one with ridges like in a rubber fuel hose where the nylon reinforcement creates ridges. Also, every
connection cause resistance in the flow especially when using ninety-degree turns/bends.
* Reduced turbulence in the flow (turbulence creates resistance and possibly micro air bubbles).
* A greater resistance of collapsing/pump under a high demand (big HP Engines) being sucked from the tank to the pump in the engine bay or from
a "Duck Butt" (pinching/kinking) that reduces the internal diameter of your supply when using rubber.
* Greatly reduced corrosion (depending on the type of fuel/chemical and the compatibility of the metal or metal coating in the pipe (be careful with E-85).
* Less likely to burn when too close to exhaust like rubber. Be fire safe! Also avoid boiling the fuel with metal tubing too close to the exhaust.
* If your pumping fuel from a pump in the tank to the engine you may also want to factor in the Head Pressure (gravity) especially with larger lifts (like a 5"
lift) with a small pump or you can use a bigger fuel pump to help offset this. Be careful when selecting a fuel pump and don't just look at the fuel
pressure rating (thinking about those fuel injected Broncos). You should also look at how much volume it pumps for your application, (thinking about
those 4-barrel Broncos) or you could find that your Bronco idles great but is starved of fuel on long acceleration or at the top end.

For some of you that like to relate things, you can think of it like helping your engine breath better with a less restrictive air intake and air filter. (since your engine is basically a big air pump). The smaller the air intake, the smaller (dirtier) air filter, the more connections, the sharper ninety degree turns, the less volume reaches your engine. It's kind of like the old pipeline goal of putting one marble at a time in the pipe and getting one marble out the other end each time. I hope this is more helpful for some. OK, since I let the cat out of the bag with air filters . . . . does this relate to those little two-dollar fuel filters (that love to clog or melt with E-85) you see near the rear drivers tire on some broncos (save those for your lawnmower)? The Coyote fuel filter on my F-150 is nearly the size of an old-fashioned coffee can. Food for thought, get it . . . coffee that fuels us. LOL

My personal experience with nylon (clear to having a milky white appearance, can turn a brownish orange with age) has a tendency to crack with age and long-term exposure to heat (I used to live in Arizona only to walk into my garage and smell gasoline in the direction of my 68 Jaguar E-Type). I also found that if you're inserting a barbed metal connection into the nylon tubing, soak the end of the tube in hot water a few minutes to soften it before you begin the wrestling match (not too hot or it will want to fold/crimp). I would highly advise to avoid heating with a flame/torch since there is really no temperature consistency and it's easy to melt (waste your materials/money. Also, when you buy the materials, buy the fresh stuff and not that antique stuff that's been sitting on the shelf for . . . since Hendy Ford walked over and put it there. LOL

My recommendation is to use the biggest compatible (type of fuel, like E-85) supply tubing/pipe without going crazy or you may find yourself with too little pressure, volume or both. Remember to "Go with the flow" that actually fits your particular application. I'd rather plumb my Bronco with a larger tubing now than wish I had it down the road when I want to upgrade. If I lost you, go to the coffee store and get a plastic stir stick (like a red swizzle stick) then go to McDonalds and order a shake (I like the chocolate shake myself). Suck the shake out of the stir stick then the straw that came with the shake and you should now understand Capacity, friction loss, volume and pressure. If you bend the straw ninety degrees, you can experience restriction. If you twist and bend the straw in a lot of places while taking a drink you will experience a kind of friction loss.

I'm thinking that I must have stayed at a Motel 6 last night (if you're old enough to remember those commercials)

OK, I need more coffer or better yet I'm going back to bed.

 

[rockinrich]

A rubber line will flex due to the fact it isn't ridged. So yes it will flex

On a carbureted motor with a solid line and mechanical pump they both are solid mounted to the motor and move in unison. Most of these types came from the factory with solid lines. Ford did use a short piece of rubber on the fuel filter instead of a flared fitting on both ends like some other manufacturers. The rest of the line was solid.

so ford didn't use nylon for their fuel lines?I'm pretty sure the lines on my bronco are factory and they are nylon with rubber at bends where needed.

 

[rockinrich]

I'm not a mechanic and my only formal automotive education was one semester of High School Auto Shop in another lifetime; so what do I know? Anyway, here's my two cents.

Since a metal tube generally has a smoother/straighter finish inside where the liquid is, there is:
* Less friction loss from a smoother tube than one with ridges like in a rubber fuel hose where the nylon reinforcement creates ridges. Also, every
connection cause resistance in the flow especially when using ninety-degree turns/bends.
* Reduced turbulence in the flow (turbulence creates resistance and possibly micro air bubbles).
* A greater resistance of collapsing/pump under a high demand (big HP Engines) being sucked from the tank to the pump in the engine bay or from
a "Duck Butt" (pinching/kinking) that reduces the internal diameter of your supply when using rubber.
* Greatly reduced corrosion (depending on the type of fuel/chemical and the compatibility of the metal or metal coating in the pipe (be careful with E-85).
* Less likely to burn when too close to exhaust like rubber. Be fire safe! Also avoid boiling the fuel with metal tubing too close to the exhaust.
* If your pumping fuel from a pump in the tank to the engine you may also want to factor in the Head Pressure (gravity) especially with larger lifts (like a 5"
lift) with a small pump or you can use a bigger fuel pump to help offset this. Be careful when selecting a fuel pump and don't just look at the fuel
pressure rating (thinking about those fuel injected Broncos). You should also look at how much volume it pumps for your application, (thinking about
those 4-barrel Broncos) or you could find that your Bronco idles great but is starved of fuel on long acceleration or at the top end.

For some of you that like to relate things, you can think of it like helping your engine breath better with a less restrictive air intake and air filter. (since your engine is basically a big air pump). The smaller the air intake, the smaller (dirtier) air filter, the more connections, the sharper ninety degree turns, the less volume reaches your engine. It's kind of like the old pipeline goal of putting one marble at a time in the pipe and getting one marble out the other end each time. I hope this is more helpful for some. OK, since I let the cat out of the bag with air filters . . . . does this relate to those little two-dollar fuel filters (that love to clog or melt with E-85) you see near the rear drivers tire on some broncos (save those for your lawnmower)? The Coyote fuel filter on my F-150 is nearly the size of an old-fashioned coffee can. Food for thought, get it . . . coffee that fuels us. LOL

My personal experience with nylon (clear to having a milky white appearance, can turn a brownish orange with age) has a tendency to crack with age and long-term exposure to heat (I used to live in Arizona only to walk into my garage and smell gasoline in the direction of my 68 Jaguar E-Type). I also found that if you're inserting a barbed metal connection into the nylon tubing, soak the end of the tube in hot water a few minutes to soften it before you begin the wrestling match (not too hot or it will want to fold/crimp). I would highly advise to avoid heating with a flame/torch since there is really no temperature consistency and it's easy to melt (waste your materials/money. Also, when you buy the materials, buy the fresh stuff and not that antique stuff that's been sitting on the shelf for . . . since Hendy Ford walked over and put it there. LOL

My recommendation is to use the biggest compatible (type of fuel, like E-85) supply tubing/pipe without going crazy or you may find yourself with too little pressure, volume or both. Remember to "Go with the flow" that actually fits your particular application. I'd rather plumb my Bronco with a larger tubing now than wish I had it down the road when I want to upgrade. If I lost you, go to the coffee store and get a plastic stir stick (like a red swizzle stick) then go to McDonalds and order a shake (I like the chocolate shake myself). Suck the shake out of the stir stick then the straw that came with the shake and you should now understand Capacity, friction loss, volume and pressure. If you bend the straw ninety degrees, you can experience restriction. If you twist and bend the straw in a lot of places while taking a drink you will experience a kind of friction loss.

I'm thinking that I must have stayed at a Motel 6 last night (if you're old enough to remember those commercials)

OK, I need more coffer or better yet I'm going back to bed.

And all that at 4:13 am! Thank you for your input,some good info!

 

[gnpenning]

so ford didn't use nylon for their fuel lines?I'm pretty sure the lines on my bronco are factory and they are nylon with rubber at bends where needed.

I have only been talking about the lines from the fuel pump to carb.

Yes, Ford used a combination of materials from the tank to the mechanical pump on the motor. .