Fuel restriction w/ 6an line?

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1969ProDart

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Ok my question is.. well I have a fuel restriction if I run a 6an hose from my FPR to my carb.
My setup (from the fuel cell to carb)

10an fitting w/ 10an line to filter
(From filter to pump) 10an fitting w/ 10an line to holley blue fuel pump
(From pump to FPR) 10an fitting w/ 10an line to holley FPR
6an fitting w/ 6an line to 6an banjo to edelbrock 1407 carb

I'm running a 383

Should I run a bigger line from the FPR or would I be fine with a 6an.
 
1969ProDart said:
Ok my question is.. well I have a fuel restriction if I run a 6an hose from my FPR to my carb.
My setup (from the fuel cell to carb)

10an fitting w/ 10an line to filter
(From filter to pump) 10an fitting w/ 10an line to holley blue fuel pump
(From pump to FPR) 10an fitting w/ 10an line to holley FPR
6an fitting w/ 6an line to 6an banjo to edelbrock 1407 carb

I'm running a 383

Should I run a bigger line from the FPR or would I be fine with a 6an.
Click to expand...

Usually you don't want to go two steps down, especially down stream from the pump and after the regulator. Theoretically, you should only have regulated fuel going to the bowls so if you have a step down after your regulator, your pressure will vary. The best place to have a step down would probably be right at the cell but realistically you should only go to -8. Also, an Edelbrock 1407 is not a real racy carb. so unless I am missing something, your delivery system is overkill.

On my car, I actually do have a single step down in my fuel line. I have a 1/2" pickup in the tank but my lines are 3/8. I used a -8 to -6 adapter right at the pickup outlet. Seems to work fine, no problems in the fuel delivery department for me. Kind of defeats the purpose of the 1/2" pickup but I'm not terribly bright sometimes.

Just out of curiosity, why are you running -10 stuff? That's a pretty huge line at 9/16 inside diameter. (-6 is basically 3/8 inside diameter) In other words, its way more than necessary on a street car or even a fairly healthy race car.
 
1969ProDart said:
Ok my question is.. well I have a fuel restriction if I run a 6an hose from my FPR to my carb.
My setup (from the fuel cell to carb)

10an fitting w/ 10an line to filter
(From filter to pump) 10an fitting w/ 10an line to holley blue fuel pump
(From pump to FPR) 10an fitting w/ 10an line to holley FPR
6an fitting w/ 6an line to 6an banjo to edelbrock 1407 carb

I'm running a 383

Should I run a bigger line from the FPR or would I be fine with a 6an.
Click to expand...
if it was a big holley, I`d say run a 06 to each end of the carb w/ fuel pressure at 6.5-7. had that set-up on a 600 horse chevy, w/ 1/2" line to reg., worked fine.-bob
 
rmchrgr said:
Just out of curiosity, why are you running -10 stuff? That's a pretty huge line at 9/16 inside diameter. (-6 is basically 3/8 inside diameter) In other words, its way more than necessary on a street car or even a fairly healthy race car.
Click to expand...

All the lines were ran when I bought the car as a roller, previous owner had a sick setup. So when I got everything I needed together it came to finishing off the fuel delivery system. Yea it's overkill for my setup, but if I do decide to go big later. It's there lol so 6 an from the fpr will fine then?
 
1969ProDart said:
All the lines were ran when I bought the car as a roller, previous owner had a sick setup. So when I got everything I needed together it came to finishing off the fuel delivery system. Yea it's overkill for my setup, but if I do decide to go big later. It's there lol so 6 an from the fpr will fine then?
Click to expand...

Again, I wouldn't step down after the reg. because it can alter your pressure to the carb. The regulator itself is sort of a restriction itself so you don't want one step from a big line to the reg. then down another step after the reg. Capiche?

That said, it would probably work OK as long as you realize that this is not the best way to skin the proverbial cat. Just make sure you are able to verify your pressure at the bowl (after your step) or you will be chasing your tail.
 
If you know the ID, you can go online and find calculators to tell you exactly what the loss is.
 
I am using -8 an from the tank to filter then to pump then to regulator. After regulater it is 2 -6an lines to 750 holley double pumper. This is on a 388ci sbc in my race car running e-85. I haven't run the car yet but from my own previous experience it should work well enough for 475-500 horses. I think a dual feed carb with two -6an lines would be better for your set up or a -8an line to carb if you must run a street carb like that.
RTR
 
rmchrgr said:
Again, I wouldn't step down after the reg. because it can alter your pressure to the carb. The regulator itself is sort of a restriction itself so you don't want one step from a big line to the reg. then down another step after the reg. Capiche?

That said, it would probably work OK as long as you realize that this is not the best way to skin the proverbial cat. Just make sure you are able to verify your pressure at the bowl (after your step) or you will be chasing your tail.
Click to expand...

So what if I put a pressure gauge between the FPR and the carb? Wouldn't that give me an exact pressure reading?
 
1969ProDart said:
So what if I put a pressure gauge between the FPR and the carb? Wouldn't that give me an exact pressure reading?
Click to expand...

I would think so, yes. But, I think you need to find a place for it after you make the step from -10 to -6. It's a little easier in this case since the 1407 is a single-feed. There are fittings available with a gauge port, just a matter of finding one that fits.

Not sure if in fact there are any fittings that will go from a -10 to -6. though, never seen one or had any reason to look for one since normally you don't step two sizes down. You will probably have to go from a -10 to 3/8 NPT or some such thing.

So your carb inlet line would probably go; regulator outlet > male -10 to -6 (however that is accomplished) > small length of -6 (or 3/8 line) > gauge fitting > bowl. Make sense?

I might be making a bigger deal than necessary about the pressure change but if it were me, I would want to ensure the bowl was in fact getting the pressure it was supposed to coming off the regulator.
 
Here's a pic of the way my regulator and pressure gauge is set up. Obliviously I have a dual feed carb so it's going to be slightly different than yours but should give you the general idea.

The inlet lines are a kit from AED. They were kind of a pain to fit. Initially the regulator was on a bracket that attached to the RF carb stud but it didn't work because the regulator was hitting the valve cover and the fittings/hose end for the line from the pump was hitting the intake runner. Ditched the bracket and it all came together without clearance issues because I was able to set it at a slight angle. Its plenty rigid without the bracket.
 

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1969ProDart said:
So theatricality tell me what's the pressure flowing through the 6an line?
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I have no idea really, I'm sure there is a way to calculate it but I'm not sure how.

The question arises though because you are adding a smaller line after the liquid has already been regulated to a certain psi. I'm not saying that this will happen but based on physics as I understand them, you will see an increase in pressure at the point of the step down, however much it is. Could be negligible, could be a couple psi, could be a lot.

Think about it - 9/16 tubing (-10) has almost double the area of 3/8 (-6) tubing for any given length. Basic physics says liquid can not be compressed therefore it has to go somewhere. Forcing a larger volume of liquid into a smaller hole HAS to change pressure. To what extent or percentage again, I don't really know. It has to be something though and will be higher than what you have coming off the regulator.

That's why you need the gauge after the step to ensure the pressure is not altered further from what you think it's supposed to be.

Sorry to be so long winded, hope that helps.
 
The system you have will be fine and a bit overkill.

The pressure doesn't change from the hose sizing, it changes within the confines of the regulator. The regulator valving separates the input and output pressures.

520px-Single-stage-regulator.svg.png


#10 is big line for a mild street car, but, you have it so use it!
 
crackedback said:
The pressure doesn't change from the hose sizing
Click to expand...

It will ABSOLUTELY change from hose size.

How much? Again, I am not sure. Probably not a whole lot in this particular case.

In any event, whether its 1 psi or 100, you will have some difference in pressure if you install tubing that will physically alter the volume of fuel flowing through it after it's already been regulated to a specific pressure, all else being equal.
 
Flow rate will change with tube diameter. Pressure is controlled by the regulator and will remain fairly steady.

What you have should work fine.
 
All of you are sort of correct. Pressure will "try" to drop under HIGH flow conditions downstream of the regulator, and if the flow is high enough, and if the tube is small enough, pressure WILL drop

Static pressure is not affected by tube size

However, unless this is a 600hp monster and or running E85, I doubt that no6 would be an issue. Hell there were some pretty impressive old-school cars ran on 5/16 line all the way from the front to the rear.........which brings up another issue...........

and that is that tube size pressure drop depends on pressure IE pressure drop is much more severe as the line LENGTHENS, and is much worse on the inlet (lower pressure) side of the pump
 
If you are referring to the friction losses causing pressure drop that will occur in any hose/piping when moving a fluid, I agree there will be some. There will be in that honking #10 feed line. It occurs in just about EVERY case, much like voltage drop in electrical lines.

Colebrook Equation, Reynolds Number, D’Arcy-Weisbach Friction Coefficient whichever you want to use it's going to happen.

IIRC, the drop in a system like this with short runs, low fluid movement rates and pressures will be so small that it would undetectable without some precise measuring systems, not some 1.5" fuel pressure gauge. You're likely talking .05 psi or less in most cases. Maybe you could figure out the actual pressure drop to educate everyone.

Totally insignificant in the big picture. Making mountains out of molehills
 
Listen, I didn't mean for this to turn in to discussion about fluid dynamics, nor is this something the OP should go nuts over. All I was saying was that the difference in tubing diameter AFTER the regulator MAY cause an issue. Just thought it was something to keep in mind should he have issues with setting float level, flooding or a rich condition. Since he is setting the pressure at point A then stepping down at point B, he may (or may not) see an unwanted difference in pressure, however much it may be. I am not an engineer though so all of this is conjecture on my part.

And again, this setup will likely work fine but it's not the optimal way to go about it. If it were me, I'd ditch the -10 stuff and start from scratch. Like myself and just about everyone else who replied here has said, it sounds like a pretty mild setup and there is no way in the world a -10 delivery line would be remotely necessary.

Only other thing I would add here is that cobbling things together like this just because 'it's there already' sometimes causes more headaches than just starting from a better point.
 
rmchrgr said:
Listen, I didn't mean for this to turn in to discussion about fluid dynamics, nor is this something the OP should go nuts over. All I was saying was that the difference in tubing diameter AFTER the regulator MAY cause an issue. Just thought it was something to keep in mind should he have issues with setting float level, flooding or a rich condition. Since he is setting the pressure at point A then stepping down at point B, he may (or may not) see an unwanted difference in pressure, however much it may be. I am not an engineer though so all of this is conjecture on my part.

And again, this setup will likely work fine but it's not the optimal way to go about it. If it were me, I'd ditch the -10 stuff and start from scratch. Like myself and just about everyone else who replied here has said, it sounds like a pretty mild setup and there is no way in the world a -10 delivery line would be remotely necessary.

Only other thing I would add here is that cobbling things together like this just because 'it's there already' sometimes causes more headaches than just starting from a better point.
Click to expand...

True, already found a solution. I'm going with it. Don't think I'll ditch the no10 stuff. It's there already, ran, and set. Looks pretty new also. I'll just put a regulator between the fpr and carb. Boom that's my final pressure before hitting the carb. I thank everyone for their input. Learned some diff I didn't know!
 
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