What size fuel line from the tank?

[that240guy]

for my ls1 I am removing all the original fuel lines all the way to the tank (carburetor car) and I am going to use the corvette fuel filter as my regulator. I am going to run a new 3/8" stainless steel hard line for my feed and my return line. I am also going to use a walbro 255 inline pump.

 

My question is, are the factory hard lines in the tank big enough to support a 500 hp engine or should I pull the tank and get 3/8" tubes welded into the tank?

[dr_hunt]

I don't know what the distance of your fuel line route is. IMO you should run 1/2" to the regulator and 3/8" back. As an example I have a Aeromotive A2000 pump on my alky system and it has a cutoff return fuel log from C&S, that is open when the throttle is closed and then shuts off the bypass valve (adjustable closure ball valve) to achieve 11psi at the carb running at WOT. With the system completely open, -10 line (5/8") to and from the fuel log, no regulator, no 90 degree fittings, I get 3.5psi pressure reading at the carb and 7psi reading at the pump in the back of the car! At WOT I'm reading 18 psi at the pump. So the line losses can be significant with enought flow which makes it harder on the pump and draws more amps.

 

The difference in cost between 3/8" and 1/2" will be minimal to the potential headaches down the road if it's not big enough to support the power your making and if it exceeds the pumps capacity to deliver at whatever your systems dynamic pressure is.

 

My new TT350 is going to use the A1000 pump, -10 feed line to the regulator, -8 return as recommended by Aeromotive for the distance I have plumbed. Even this pump may not be enough when I'm done, in which case I'll add another one.

[that240guy]

I definately don't need half inch line for a fuel injected 500 hp application. 3/8 line can support 750 hp+. I just want to make sure that the lines coming out of the tank are adequate.

 

Any input?

[Lason]

3/8 line can support 750 hp+. I just want to make sure that the lines coming out of the tank are adequate.

 

Any input?

 

I dont know where you get all that info from. I have had fuel issues with a '90 mustang running around 520hp on the bottle and had to upgrade to -10 feed/return to get it to keep up. Now that is the standard size I go with and will be whats on my LS1 Z. Some people run a smaller return but I have no idea why. I would rather have my whole system one size so I dont have to stock 2 sizes of fittings etc. And there is no such thing as too big of a return line.

[that240guy]

2003-04 ford cobras run 3/8 line and with the bowzilla kit that utilizes the stock fuel lines, these cars are making 650+ hp to the wheels without starvation problems. My best friends camaro is putting down 680 hp to the wheels on stock fuel line and a stock fuel pump with just an auxiliary inline fuel pump. My boss's chevelle makes 800 hp on -6 fuel line. I think you have other issues with your mustang.

[piston]

i was wondering if anyone of you guys run straight 3/8 fuel line without steel braided from the tank to the carb/fuel rail? and also by running the smaller fuel return, im assuming it would bump up the psi on the regulator? just wondering cause im thinking about running 3/8 regular fuel line from tank to fuel rail...

[dr_hunt]

 

Well that depends on pressure, but from the above chart you can see which pump you are running.

 

Absolute Maximum Horsepower at 12 volts free flowing at zero psi, the standard pump is 644HP. So, if you figure in line losses, fitting loss and fuel bowl needle and seat losses, your going to be cutting it real close, probably too close IMO if your using the standard pump, the HP pump is alot better and would work IMO. That is what we were talking about anyway was the use of the walbro 255lph pump, not line size capability. The best recomendation is to check with the manufacturer or dealer to get the information on their pumps. Only this way can you be sure that you are getting a pump that will safely support the horsepower you plan to make.

[Turbo Meister]

And there is no such thing as too big of a return line.

 

I agree. Had to change my return line to 10 AN because the 8 AN line would not bypass enough fuel back to the tank. As a result, the 8 line caused too much fuel pressure to back up, my regulator could not handle it while sitting in traffic.

 

DR Hunt, you need 10 AN return line for your application, if you drive in traffic.

Hanns

[dr_hunt]

I agree. Had to change my return line to 10 AN because the 8 AN line would not bypass enough fuel back to the tank. As a result' date=' the 8 line caused too much fuel pressure to back up, my regulator could not handle it while sitting in traffic.

 

DR Hunt, you need 10 AN return line for your application, if you drive in traffic.

Hanns[/quote']

 

Traffic? What is that? Is that something that you all have in California that nobody else has? I've heard of that traffic stuff, just never seen it before. Does it include horses and cows? If so we have the same here, no biggie, I just honk the horn, what do you all do?

 

With the solid roller cam I have, I doubt it'll see much street action at all. I decided to intercool it ala James Thagard and go serious on boost! If I sit at a light in socorro it isn't for very long and we HAVE to cruise sonic to find this 9 second daily driven dodge dart with a 440 in it! Supposedly all motor, drives it 30 or 40 miles to town and back everyday, runs consistent low 9's according to rumors. I've seen it, just not while driving anything remotely fast, it looks like a stink bug with the rear end 4 feet off the ground and front bumper almost dragging the pavement to clear the 9 or so inch wide 28 inch tall ET Streets on the back.

[Pop N Wood]

Here is a pretty good link Grumpy once posted

 

http://www.centuryperformance.com/fuel.asp

 

They do a pretty good job of explaining pump ratings. Note that return systems can use a smaller pump than the dead head systems. The caution about using restrictive fittings. They also recommend the same size feed and return.

 

But their reccomended line sizes are about a step larger than anyone else I have seen. They say 1/2 line is needed for anything above 375 HP.

 

I am picking up a Mallory Comp 140 gph fuel pump. I will be using the Mallory recomended 3/8 inch feed and return line with this pump. I will probably never grow to more than 500 NA HP.

 

And as everyone knows, alcohol requires more fuel for the same HP than gas.

[piston]

so what if i run stock lines with a walbro 255 fuel pump? hp will be at no more than 360hp for the time of being. i know the walbro 255 does bring up the pressure by 3-5psi because i use to run one and will probably be running another one in the z. will it be safe on stock lines since the walbro for sure should supply enough fuel for the lt1.

[Lason]

2003-04 ford cobras run 3/8 line and with the bowzilla kit that utilizes the stock fuel lines, these cars are making 650+ hp to the wheels without starvation problems. My best friends camaro is putting down 680 hp to the wheels on stock fuel line and a stock fuel pump with just an auxiliary inline fuel pump. My boss's chevelle makes 800 hp on -6 fuel line. I think you have other issues with your mustang.

 

Well that mustang is long gone. Im just speaking from personal expirience. All we did is run -10 feed/return line using the same A1000 pump and reg and my lean spot up top went away. All using a wideband A/F on a dyno.

 

Point being, why would you skimp on the size? Too big of a feed/return wont hurt you, only give you peace of mind that you wont be maxing it out.

[dr_hunt]

You should be alright for 360HP. The important thing is to check with the pump manufacturer before you buy.

 

I checked with aeromotive before laying out my system and for my application my system is designed based on their recommendation. However if it doesn't work, it can be fixed so that it does. They say the A1000 will support 1200HP carb'd forced induction, although their literature doesn't say that, we'll see, I may have to step up to the eliminator pump, but that is if this combination will produce that kind of HP, which is a big if at this stage. I'd be happy with 1000HP in the Monte which should lay down 800HP+ to the wheels, which should put me in the low 10's which is where I want it to be. Well, maybe high 9's, ok, so I'm greedy, which is why I went to James Thagard!

[Phantom]

FWIW - My LS1 is using the original stock 280Z supply and return lines - just with a higher pressure pump, 60 psi vs 35. It dyno'd 311 at the rear wheels which maths to about 390 at the flywheel. The only time I've had fuel starvation problems was in hard corners on the track and less the 1/4 tank of fuel - which wasn't a fuel line size problem.

[sweetleaf]

Yes but the 240Z tank has smaller in/out tubes on the tank. Witch in my opinion are too small and cause exsessive strain on the pump. You can either replace the tank with a later modle fuel injected tank or put in a fuel cell. Other options are to run your feed line off the bottom drain hole or weld a sump pan to the bottom.

[wheelman]

The feed line in the 240Z tank is 5/16" which is to small especially when you consider the inline pump will have to draw a siphon to get the fuel up out of the tank. I had a 240 tank with a sump that had two 3/8" outlets that fed my Walbro 255lph inline pump but the line running from the sump to the pump was routed around the end of the tank so it went up then back down. This caused the pump to get pretty noisy if the tank was close to empty and the car would run like $hit. Anyway I replaced the 240 tank with an LS1 Camaro tank (more to eliminate the leaks than because of the pump) and have not had the problem when the fuel level is low. I used 3/8" feed and return lines and with the Datsun tank used the original 5/16" feed connection at the tank as the return.

 

Hope this makes sense and answers the original question about the size of the feed connection on the 240 tank.

 

One last thing, I would not go any smaller than 3/8 line on feed and return.

 

Wheelman

[Pop N Wood]

Yes but the 240Z tank has smaller in/out tubes on the tank. Witch in my opinion are too small and cause exsessive strain on the pump. You can either replace the tank with a later modle fuel injected tank or put in a fuel cell. Other options are to run your feed line off the bottom drain hole or weld a sump pan to the bottom.

 

Piss. Double piss with what Wheelman said. Was hoping to get a short term short cut to getting on the road.

 

The fill tubes on the 240 tank are suppose to be soldered in. Has anyone unsoldered the fill and return tubes (along with their mounting plate) and rigged up a larger inch pick up?

 

You guys scare me with your 1/2 lines. The Comp 140 pump I am looking at for my carb motor only recommends 3/8 inch feed and return. Every damn splitter I have seen for Holley carbs use 3/8 inch line. Whay would something under 500 HP (which is probably 98% of the guys on here) need 1/2 inch line?

 

And from what I have read the overwhelming majority of guys are using 3/8 line. Hell, a lot of guys aren't even running return lines.

[Guest Mike]

Hey Pop,

 

This is amuZing:) I'm following this thread because I know nothing of fluid dynamics and need help with this too. If this thread stays alive long enough, we'll sort through the answers and have a pretty good idea of what to do in our particular applications.

 

What I need is precise scientific data to support these suggestions. Empirical data is needed too because real-world experiences often differ from mathematical equations and theory. I just need to see the math...

 

HEY DR_HUNT... are you familiar with fluid dynamics???

 

Piss. Double piss with what Wheelman said. Was hoping to get a short term short cut to getting on the road.

 

The fill tubes on the 240 tank are suppose to be soldered in. Has anyone unsoldered the fill and return tubes (along with their mounting plate) and rigged up a larger inch pick up?

 

You guys scare me with your 1/2 lines. The Comp 140 pump I am looking at for my carb motor only recommends 3/8 inch feed and return. Every damn splitter I have seen for Holley carbs use 3/8 inch line. Whay would something under 500 HP (which is probably 98% of the guys on here) need 1/2 inch line?

 

And from what I have read the overwhelming majority of guys are using 3/8 line. Hell, a lot of guys aren't even running return lines.

[Lason]

Whay would something under 500 HP (which is probably 98% of the guys on here) need 1/2 inch line?

 

We dont but in my case I will be surpassing the 500hp point sooner before later so Im planning ahead. Like I said, it only cost a lil more than running -8 lines so why not. I already have -10 wrenches, fittings and a few other things from past projects so its just easier in my case. You can probably get away with 3/8" line and never need to go any bigger but if you do then that is just double $$$ in the long run to re-do everything.

[Guest Mike]

Hey Doc,

 

Do you have the basic equations for fluid flow with specifity to the viscousity of typical American gasoline at say... 0-120 degrees Farenheit? I like charts but equations are more versatile... unless you have lots of charts:mrgreen: I'd like to see equations on how impedences created by various junctures affect flow as well. Any idea as to whether it's better to push fuel through the lines... or pull it? How does ambient temperature affect the disparate types of pumps?

 

 

Well that depends on pressure, but from the above chart you can see which pump you are running.

 

Absolute Maximum Horsepower at 12 volts free flowing at zero psi, the standard pump is 644HP. So, if you figure in line losses, fitting loss and fuel bowl needle and seat losses, your going to be cutting it real close, probably too close IMO if your using the standard pump, the HP pump is alot better and would work IMO. That is what we were talking about anyway was the use of the walbro 255lph pump, not line size capability. The best recomendation is to check with the manufacturer or dealer to get the information on their pumps. Only this way can you be sure that you are getting a pump that will safely support the horsepower you plan to make.