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Re: 3/8" return line, how much will it support ?
[Re: AlexP]
#34008
01/16/07 04:43 AM
01/16/07 04:43 AM
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Joined: Jan 2003
Posts: 8,180
Detroit, MI
CokeBottleKid
master
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master
Joined: Jan 2003
Posts: 8,180
Detroit, MI
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 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....
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Re: 3/8" return line, how much will it support ?
[Re: Bigcube]
#34011
01/16/07 10:46 AM
01/16/07 10:46 AM
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Joined: Feb 2003
Posts: 12,675
Columbia, CT
moper
I Live Here
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I Live Here
Joined: Feb 2003
Posts: 12,675
Columbia, CT
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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.
Well, art is art, isn't it? Still, on the other hand, water is water! And east is east and west is west and if you take cranberries and stew them like applesauce they taste much more like prunes than rhubarb does. Now, uh... Now you tell me what you know.
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Re: 3/8" return line, how much will it support ?
[Re: Bigcube]
#34012
01/16/07 11:12 AM
01/16/07 11:12 AM
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Joined: Jan 2003
Posts: 32,394
Quicktree
I Win
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I Win
Joined: Jan 2003
Posts: 32,394
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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.
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Re: 3/8" return line, how much will it support ?
[Re: Bigcube]
#34016
01/16/07 08:59 PM
01/16/07 08:59 PM
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Joined: Jun 2003
Posts: 9,225
Charleston
sixpackgut
Drag Week Mod Champion
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Drag Week Mod Champion
Joined: Jun 2003
Posts: 9,225
Charleston
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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
Last edited by sixpackgut; 01/16/07 09:02 PM.
Gen 3 power 6.22@110, 9.85@135
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performance only racing, CRT, ultimate converter, superior design concepts, ThumperCarbs
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Re: 3/8" return line, how much will it support ?
[Re: BobR]
#34018
01/16/07 09:32 PM
01/16/07 09:32 PM
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Joined: Sep 2005
Posts: 2,179
California, USA
blairboy3
top fuel
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top fuel
Joined: Sep 2005
Posts: 2,179
California, USA
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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.
1968 Plymouth Fury III 4-Door: 12.79 @ 115, 60'- 1.93 (Hey... it's a Cruise ship... what do you expect?!) Famoso Raceway, 02/08
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Re: 3/8" return line, how much will it support ?
[Re: blairboy3]
#34019
01/16/07 09:35 PM
01/16/07 09:35 PM
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Joined: Jun 2003
Posts: 9,225
Charleston
sixpackgut
Drag Week Mod Champion
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Drag Week Mod Champion
Joined: Jun 2003
Posts: 9,225
Charleston
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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
Last edited by sixpackgut; 01/16/07 09:39 PM.
Gen 3 power 6.22@110, 9.85@135
Follow @g3hemiswap on instagram
performance only racing, CRT, ultimate converter, superior design concepts, ThumperCarbs
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Re: 3/8" return line, how much will it support ?
[Re: RobbMc]
#34023
01/17/07 12:15 AM
01/17/07 12:15 AM
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Joined: Sep 2003
Posts: 10,645
Houston, Tx
AlexP
OP
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OP
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Houston, Tx
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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 ?
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Re: 3/8" return line, how much will it support ?
[Re: RobbMc]
#34025
01/17/07 08:03 AM
01/17/07 08:03 AM
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Joined: Jan 2003
Posts: 32,394
Quicktree
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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 
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