Posted By: AlexP
3/8" return line, how much will it support ? - 01/16/07 06:46 AM
How much power will a 3/8" return line support in a low pressure carburetor application ?
3/8" return line, how much will it support ?
Posted By: CokeBottleKid
Re: 3/8" return line, how much will it support ? - 01/16/07 08:43 AM
hmmmm if your pump supplies enough fuel for 2000HP and your supply line supports 2000HP and your motor needs 2000HP... your return line can be gone 
.Course once you let off the throttle you'll be swimming in fuel
.Point is there isn't really a direct correlation between return line size and HP.... It's always nice to have more though....
Posted By: Quicktree
Re: 3/8" return line, how much will it support ? - 01/16/07 11:42 AM
the return line on a bypass system should be bigger than the feed. at least a -10. 
Posted By: Bigcube
Re: 3/8" return line, how much will it support ? - 01/16/07 12:18 PM
Quote:
the return line on a bypass system should be bigger than the feed. at least a -10.
I've seen people saying the return should be bigger, that's not the way Product Engineering recomends building a fuel system. I run -10 from the pump to the regulator and -8 as a return.
Posted By: moper
Re: 3/8" return line, how much will it support ? - 01/16/07 02:46 PM
I'll second the "it should be bigger" deal. Well, at least AS BIG as the feed. But truthfully, that is so when you are looking at your fuel pressure, it is a true reading. Pressure is resistance to flow. So you will always show more pressure than what you really have if the return is smaller. Think of it as a "leaking deadhead" system..lol. In a true return style system, your pumps are so big becuase they have to overcome the G forces of the fuel sloshing backwards too. I dont know of too many engines at full throttle that can ingest the full output of 70 gph of even the small cheapo pumps.
Posted By: Quicktree
Re: 3/8" return line, how much will it support ? - 01/16/07 03:12 PM
Quote:Quote:
the return line on a bypass system should be bigger than the feed. at least a -10.
I've seen people saying the return should be bigger, that's not the way Product Engineering recomends building a fuel system. I run -10 from the pump to the regulator and -8 as a return.
pm RobbMc and ask him he's an engineer that designs fuel systems and such. this is some stuff he wrote a while back.
Whenever you run a low pressure pump and no regulator, there will be a pressure drop during acelleration. Even if you ran a 250 pump and somehow set the pressure of the pump low enough to run without a regulator, you would get a pressure drop because the pump must be at the back of the car and the carb is at the front and there is a pressure drop between the two as the flow increases. The pump is still putting out 6.5 psi (assuming the pump is big enough) even when the pressure at the carb has dropped to 3 psi. To make it work right, you must run a regulator.
Having said all of that, the 110 pump ain't gonna do it, even if you add a regulator. The 110 will support about 550-600 hp when used with a return regulator (it cannot be used with a dead-head because the pump internal bypass won't adjust high enough). But if you are in the 750 hp range, you are going to need to use a 140 pump and a return regulator or a 250 pump and either type of regulator (although a return regulator is always better).
If I were you, this is what I would do: Run -10 lines from the tank to a large filter and then to a 250 pump. The -10 lines on the vacuum side of the pump will prevent cavitation, especially on hot days. Then run -8 lines from the pump up to the return regulator mounted in the engine compartment. (The feed line can be smaller because it is under pressure). Use the large Mallory return regulator, not the little 4309. Then run -6 or -8 up to the carbs. Use the -10 line you are now using as a supply line as the return line from the regulator back to the tank. Return regulators are very sensitive to back pressure in the return line so you need a -10 line with a 250 pump.
After everything is hooked up, check the back pressure in the return line: With the engine off, turn on the pump. Remove the adjustment screw from the regulator so there is no load on the spring at all. The pressure gage is now showing you the back pressure in the return system. Ideally it should be zero but that's nearly impossible. As long as it is under 3 psi the system will work reasonably well. With a 250 pump and -10 lines you should have less than 2 psi backpressure. If not, find the restrictions and remove them.
With this system the fuel pressure will never drop more than 2 psi at 1200 hp. With 750 hp the pressure will never drop more than 1 psi (the less back pressure in the return line, the less the pressure will drop under load; assuming you don't outrun the pump, which won't happen with a 250 pump).
A 250 pump will generally last about 50,000 miles if you filter the fuel and run a return regulator.
Posted By: Bigcube
Re: 3/8" return line, how much will it support ? - 01/17/07 12:33 AM
Well I have a Product Engineering pump and regulator set up and I've plumbed it as they recomend, I still can't see how a larger return line is effective if you want want's of fuel up there. 
This is how PE want's you to plumb it
This is how PE want's you to plumb it
Posted By: AlexP
Re: 3/8" return line, how much will it support ? - 01/17/07 12:46 AM
I want to run a 1/2" feed, 3/8" return, a bypass regulator, 1/2" in-tank pick up, stock tank and a Walbro GSL395 pump.
Here is the flow graph on the pump.
Here is the flow graph on the pump.
Posted By: FastmOp
Re: 3/8" return line, how much will it support ? - 01/17/07 12:53 AM
The best way is to check it like said above, hook it up, pull the adjuster and see where it's at with no load.
I agree with bigcube, you never need a bigger then supply line for return. Mine is -10 up, and -8 retun.
I agree with bigcube, you never need a bigger then supply line for return. Mine is -10 up, and -8 retun.
Posted By: sixpackgut
Re: 3/8" return line, how much will it support ? - 01/17/07 12:59 AM
Quote:
Well I have a Product Engineering pump and regulator set up and I've plumbed it as they recomend, I still can't see how a larger return line is effective if you want want's of fuel up there.
i'm sure there may be a difference between the way Product engin and mallory designed there bypass regulators. thats the difference.
on the mallory system, YES, they want you to run a line as large or larger than the feed line.
i have 1/2 out of fuel tank than -8 feed line and -8 return line and it works perfect. this is a mallory 140 pump and 4309( i think) bypass regulator.
also, per ROBMC's advice, my regulator is after the fuel log
Posted By: BobR
Re: 3/8" return line, how much will it support ? - 01/17/07 01:10 AM
I agree with bigcube, you never need a bigger then supply line for return. Mine is -10 up, and -8 retun.
Man! Why is it that when good info is posted(Quicktree) there is always one or more than one person who will dispute it. I'm sure you did your doctoral thesis on fluid dynamics. THE FACT is to PROPERLY plumb a return style system/regulator your return line must be AT LEAST the same size as the feed line and preferably 1 size larger. True return style regulators are back pressure sensitive and will not work correctly if there is any measurable backpressure on the return side. PERIOD. If doing it incorrectly works for you great but I think it is best to do it right up front to eliminate this area as a point of future problems. -Bob
Posted By: blairboy3
Re: 3/8" return line, how much will it support ? - 01/17/07 01:32 AM
So, why do Fuel cell manufacturers make the cells w/ a return smaller than the supply? Not trying to 
, just wondering. I've seen a few of these posts, and wondered why the "Racing" fuel cells aren't plumbed the way you & others say they should be? I've also noticed that a lot of return style regulators have smaller -AN return ports than the supply port.
, just wondering. I've seen a few of these posts, and wondered why the "Racing" fuel cells aren't plumbed the way you & others say they should be? I've also noticed that a lot of return style regulators have smaller -AN return ports than the supply port.
Posted By: sixpackgut
Re: 3/8" return line, how much will it support ? - 01/17/07 01:35 AM
Quote:
So, why do Fuel cell manufacturers make the cells w/ a return smaller than the supply? Not trying to , just wondering. I've seen a few of these posts, and wondered why the "Racing" fuel cells aren't plumbed the way you & others say they should be?
for big pumps with bypass lines and dead head systems. i would assume thats the reason that BIGCUBES system is run with a smaller return because it actually runs a bypass and return line
Posted By: FastmOp
Re: 3/8" return line, how much will it support ? - 01/17/07 01:43 AM
My car must be magic then because wile it was flowing a huge volume through it before I started screwing in the regulator, the more I screw'd it in the less flow it had to the point that it was spraying out very hard but not very much volume at all. I use a Weldon regulator so it might have some built in voo-doo 
Posted By: Bigcube
Re: 3/8" return line, how much will it support ? - 01/17/07 03:46 AM
Yes, I run a -8 bypass off the pump and also a return style regulator with a -8 return, perhaps that's why I dosn't have any issues There is nitrous "like" jet's in the high pressure side of the regulator and smaller jet's in the low pressure side, there is only just so much fuel that can flow though the return 
There is nitrous "like" jet's in the high pressure side of the regulator and smaller jet's in the low pressure side, there is only just so much fuel that can flow though the return
Posted By: RobbMc
Re: 3/8" return line, how much will it support ? - 01/17/07 04:00 AM
The size of the feed line is dependent on the horsepower the engine produces. The size of the return line depends on the size of the fuel pump, regardless of the hp or the size of the feed line. A larger pump requires a larger feed line to return the unused fuel back to the tank.
The following is from a magazine article I wrote about ten years ago:
"The minimum fuel line size (from the pump to the regulator) is dependent on the horsepower output of the engine (and/or Nitrous system) regardless of the size of the pump.
* Up to 250HP = 5/16" or -04 AN
* Up to 375HP = 3/8" or -06 AN
* Up to 550HP = 1/2" or -08 AN
* Up to 800HP = 5/8" or -10 AN
* Up to 1200HP = 3/4" or -12 AN
If you use a return-style regulator, you will also need a return line from the regulator back to the tank. The size of the return line is dependent on the size of the pump you are using, regardless of the engine's horsepower output. The return line must have limited or NO pressure in it. In many cases, the minimum return line size will match that of the supply line, but a larger return line is sometimes required if the pump is larger than necessary.
* Up to 45GPH = 5/16" or -04 AN
* Up to 90GPH = 3/8" or -06 AN
* Up to 200GPH = 1/2" or -08 AN
* Up to 360GPH = 5/8" or -10 AN
* up to 720GPH = 3/4"or -12 AN
The following is from a magazine article I wrote about ten years ago:
"The minimum fuel line size (from the pump to the regulator) is dependent on the horsepower output of the engine (and/or Nitrous system) regardless of the size of the pump.
* Up to 250HP = 5/16" or -04 AN
* Up to 375HP = 3/8" or -06 AN
* Up to 550HP = 1/2" or -08 AN
* Up to 800HP = 5/8" or -10 AN
* Up to 1200HP = 3/4" or -12 AN
If you use a return-style regulator, you will also need a return line from the regulator back to the tank. The size of the return line is dependent on the size of the pump you are using, regardless of the engine's horsepower output. The return line must have limited or NO pressure in it. In many cases, the minimum return line size will match that of the supply line, but a larger return line is sometimes required if the pump is larger than necessary.
* Up to 45GPH = 5/16" or -04 AN
* Up to 90GPH = 3/8" or -06 AN
* Up to 200GPH = 1/2" or -08 AN
* Up to 360GPH = 5/8" or -10 AN
* up to 720GPH = 3/4"or -12 AN
Posted By: AlexP
Re: 3/8" return line, how much will it support ? - 01/17/07 04:15 AM
I want the basic system minus the pump to be 600hp capable. It just ticks me off because I would really like to be able to use the new 3/8" I already bought, but I think I am just going to have to bite the bullet and get a 1/2" return line done now.
I am going to get it all in SS from Inline tube, and Dante is going to get back to me tomorrow to see if Inline will discount the custom items. If so, 15% off of a $280 order is nothing to sneeze at.
Rob, with the fuel pump I will be using and the other dimensionally similar Walbro pumps available, in your personal opinion do you think that I should use the 3/8" or 1/2" return line for this specific instance ?
I am going to get it all in SS from Inline tube, and Dante is going to get back to me tomorrow to see if Inline will discount the custom items. If so, 15% off of a $280 order is nothing to sneeze at.
Rob, with the fuel pump I will be using and the other dimensionally similar Walbro pumps available, in your personal opinion do you think that I should use the 3/8" or 1/2" return line for this specific instance ?
Posted By: Stroker Scamp
Re: 3/8" return line, how much will it support ? - 01/17/07 06:25 AM
i run an aeromotive pump 10 an on the supply and 10 an on the return from the bypass regulator 
Posted By: Quicktree
Re: 3/8" return line, how much will it support ? - 01/17/07 12:03 PM
Quote:
The size of the feed line is dependent on the horsepower the engine produces. The size of the return line depends on the size of the fuel pump, regardless of the hp or the size of the feed line. A larger pump requires a larger feed line to return the unused fuel back to the tank.
The following is from a magazine article I wrote about ten years ago:
"The minimum fuel line size (from the pump to the regulator) is dependent on the horsepower output of the engine (and/or Nitrous system) regardless of the size of the pump.
* Up to 250HP = 5/16" or -04 AN
* Up to 375HP = 3/8" or -06 AN
* Up to 550HP = 1/2" or -08 AN
* Up to 800HP = 5/8" or -10 AN
* Up to 1200HP = 3/4" or -12 AN
If you use a return-style regulator, you will also need a return line from the regulator back to the tank. The size of the return line is dependent on the size of the pump you are using, regardless of the engine's horsepower output. The return line must have limited or NO pressure in it. In many cases, the minimum return line size will match that of the supply line, but a larger return line is sometimes required if the pump is larger than necessary.
* Up to 45GPH = 5/16" or -04 AN
* Up to 90GPH = 3/8" or -06 AN
* Up to 200GPH = 1/2" or -08 AN
* Up to 360GPH = 5/8" or -10 AN
* up to 720GPH = 3/4"or -12 AN
this should be saved
Posted By: BobR
Re: 3/8" return line, how much will it support ? - 01/17/07 02:48 PM
"this should be saved"
This arguement will come up again(like it has 1000 times before). There will still be folks who will dispute anything that may be different than what they have. -Bob
This arguement will come up again(like it has 1000 times before). There will still be folks who will dispute anything that may be different than what they have. -Bob
Posted By: RobbMc
Re: 3/8" return line, how much will it support ? - 01/17/07 05:11 PM
Quote:
I want the basic system minus the pump to be 600hp capable. It just ticks me off because I would really like to be able to use the new 3/8" I already bought, but I think I am just going to have to bite the bullet and get a 1/2" return line done now.
I am going to get it all in SS from Inline tube, and Dante is going to get back to me tomorrow to see if Inline will discount the custom items. If so, 15% off of a $280 order is nothing to sneeze at.
Rob, with the fuel pump I will be using and the other dimensionally similar Walbro pumps available, in your personal opinion do you think that I should use the 3/8" or 1/2" return line for this specific instance ?
Well, if I understand you correctly, you are going to use a single Walbro pump that produces only 45 gph freeflow. Is that correct? I don't think 45 gph is gonna do it for a 600hp application. I'd like to see at least 100 gph, even with a return regulator.
But, to answer your question directly, if you were to run a 45 gph pump, a 5/6" return line would work (assuming no more than 10 feet of line and no sharp bends).
Posted By: 70Dustmite440
Re: 3/8" return line, how much will it support ? - 01/17/07 05:31 PM
Quote:
True return style regulators are back pressure sensitive and will not work correctly if there is any measurable backpressure on the return
never understood before but...
im starting to understand.........
Posted By: 71Chip
Re: 3/8" return line, how much will it support ? - 01/17/07 07:02 PM
So I need a little help here...
About 6 months ago in excitement I ordered the parts for my fuel system. I bought a mallory 140 pump that is rated at 12 psi. The kit says use 3/8" or larger line, but it is plumbed for a 3/8" line. Is there any point to using a larger line then? I'm guessing maybe I can get a 1/2" fitting?
I'm a college student and on a budget and it would suck to have to buy all new 1/2" line let alone a new pump. I don't think I can still return this one.
I am anticipating 550hp.
About 6 months ago in excitement I ordered the parts for my fuel system. I bought a mallory 140 pump that is rated at 12 psi. The kit says use 3/8" or larger line, but it is plumbed for a 3/8" line. Is there any point to using a larger line then? I'm guessing maybe I can get a 1/2" fitting?
I'm a college student and on a budget and it would suck to have to buy all new 1/2" line let alone a new pump. I don't think I can still return this one.
I am anticipating 550hp.