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Old 12-08-2011, 09:25:39 PM   #1
DoTheDew
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Food for thought; fuel pressure

Progressing on my first LS swap, and am beginning work on the fuel system. This is not my camaro, but the same principle still applies I think.

Using an intake walbro 255lph pump I bought for about $120 shipping included. Its pumping fuel up through a stock sending unit, which is tied via high pressure rubber hose (18" or so) to the back end of the corvette fuel pressure regulator/filter (Wix 33737). Have a dorman repair peices to connect the high pressure rubber to the filter itself, and a factory gm line to run foward from the filter to the engine fuel rails.

However my question is for the return portion of the system. Is there, or would there be, any fuel pressure in the return section whatsoever?

I know the filter bumps pressure up to 58 give or take, but that would be on the fuel delievery line. what about the return line? There is no resistance on the return leg back to the tank, other than a few bends and twists. However the intake feed of the filter is 3/8ths, and the return only 5 1/6ths. Inside the tank, it just dumps out the bottom of the sending unit. Therefore if nothing is really "deadheading" the return, there should be little to no pressure there, correct?

Reason I ask has to due with the way I'm laying out my fuel lines. The return line may be run a little farther, and little longer than the feed line (due to chassis restraints). Purchasing high pressure rubber fuel hose is expensive, where low pressure (20psi or less) regular line, is much more economical. If there is little/no pressure on the return line side, would there be any harm in this?

And if anyone is curious, yes, I am just that cheap. Don't want to spend money if I don't have too.
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Old 12-08-2011, 10:44:26 PM   #2
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The return line is a low pressure line. That said, if it is truly going to be a long line, buy some aluminum solid line. 25 ft only cost $19.
I try not to run long rubber fuel lines whether they are EFI rated or not.
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Old 12-09-2011, 02:35:00 AM   #3
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If you are using the Wix 33737 why not just mount it just past the pump and close to the tank making for a short return line.
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Old 12-09-2011, 04:01:43 AM   #4
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Quote:
Originally Posted by speed_m5
If you are using the Wix 33737 why not just mount it just past the pump and close to the tank making for a short return line.

thats what i did. flipped the mount around and used the rear drivers side tank strap bolt.
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Old 12-09-2011, 11:18:50 AM   #5
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Quote:
Originally Posted by schitzo
The return line is a low pressure line. That said, if it is truly going to be a long line, buy some aluminum solid line. 25 ft only cost $19.
I try not to run long rubber fuel lines whether they are EFI rated or not.

Never run aluminum line for a fuel line set up. The rubber hoses should never be ran any longer than 12-18".
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Old 12-09-2011, 11:24:33 AM   #6
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Quote:
Originally Posted by hessdawg
thats what i did. flipped the mount around and used the rear drivers side tank strap bolt.

This is what I did for my fuel filter/regulator. It is mounted close to the tank on the trunk pan, using about 12" of EFI rated hose for both the lines to the tank. The line to the engine was fabricated using the fuel line from a late 80's Camaro. The connectors from the filter to the hoses was fabricated from a GM FWD vehicle.

http://www.chevythunder.com/2010%20p...%20install.jpg
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Old 12-09-2011, 12:08:14 PM   #7
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After learning about fuel stench from rubber fuel lines I'll never use them again.
I purchased stainless braided rubber fuel lines for my first LS1 swap.
Those are coming out in the near future.

I would only use PTFE (Teflon) lines or the new flexible OEM polymer fuel lines.
#1 it makes like a whole HELL of alot easier running the lines over solid steel.
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Old 12-09-2011, 05:40:45 PM   #8
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Quote:
Originally Posted by Leonards78LT
Never run aluminum line for a fuel line set up.
Why is that?
Please don't tell me "fatigue cracks"
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Last edited by schitzo : 12-09-2011 at 05:44:45 PM.
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Old 12-09-2011, 06:03:32 PM   #9
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Quote:
Originally Posted by schitzo
The return line is a low pressure line. That said, if it is truly going to be a long line, buy some aluminum solid line. 25 ft only cost $19.
I try not to run long rubber fuel lines whether they are EFI rated or not.

Forgot to mention the application. Its not my camaro, but an old 86 3/4 chevy. These trucks has side saddle tanks that bolted to the frame, tucked in tight to the back of the cab and bed. In order to be able to drop/install them, lines from the sending unit to the attachment point (fuel line, tank switching valve, or in this case, fuel pressure regulator) have to be a bit longer than normal, minimum 12", more you have, the easier it is. Unless you are extremely ambidextrous, its difficult to feed the lines up and over the fuel rail, keeping wiring harness from snagging, balancing a large tank into a tight area, threading bolts into a moving tank balanced on your knees/chest, on your back while the dog licks at your face and its snowing outside....well, its not an easy task.

If I had the resources, I would run braided line, or new nylon (likely in the spring when I aquire the special tools). However it would take about 2 months of ordering, shipping, waiting, trying, returning different fittings to make everything work nice and neat. I will get to that someday, however, for the time being (winter months) rubber can and will suffice.

Don't want to do it twice, but I'm getting sick of pumping the gas and balancing the choke to get the thing started every morning when its already -20 below up here. I look foward to simply flipping the key and have it fire right up, soon I can get there, the better.
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Old 12-09-2011, 06:12:41 PM   #10
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Fair enough but I will leave you with two of my rules when working on fuel systems
1. When in doubt follow the OEMs
2. Take no short cuts or skimp on your fuel system.
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Old 12-10-2011, 12:10:14 AM   #11
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Quote:
Originally Posted by schitzo
Why is that?
Please don't tell me "fatigue cracks"

Name me one vehicle manufacturer that uses aluminum line for fuel? There is a reason for it besides fatigue, such as corrosion.

If you can I will shut my pie hole.
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Old 12-10-2011, 12:50:58 AM   #12
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Quote:
Originally Posted by Leonards78LT
Name me one vehicle manufacturer that uses aluminum line for fuel?
You also don't see vehicle manufacturers selling their cars with nitrous systems hooked up. That doesn't mean it should not be done.


Car manufacturers may not use aluminum fuel lines but they are common place in aviation.
There are many aircraft builders that use aluminum both for various fuel lines.

Choosing the appropriate alloy to plumb your system and plumbing it appropriately should negate corrosion and or fatigue issues.
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Old 12-10-2011, 11:18:35 AM   #13
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Quote:
Originally Posted by schitzo
Car manufacturers may not use aluminum fuel lines but they are common place in aviation.
There are many aircraft builders that use aluminum both for various fuel lines.

He's got a point.

All of your AN fittings used today are "Army / Navy" spec fittings designed for aircraft back in the day made out of aluminum too.
I think they changed it to AN = Air Force / Navy these days though.

Aircraft line is rated for faaaaar higher PSI then a car uses.
http://www.mechanicsupport.com/tube_strength.html

Besides, think about it......how can an OEM plastic fuel line be safe if a metal aluminum one isn't ??
I learned alot this summer researching everything from Aluminum to PTFE to OEM Polymer fuel lines.
Steel lines are outdated and I didn't want the risk of corrosion.
Today's steel isn't the same quality of years gone by IMO, not to mention it's a PITA to route with a body on.
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Last edited by Aceshigh : 12-10-2011 at 11:27:13 AM.
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Old 12-10-2011, 06:40:57 PM   #14
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We've moved on to titanium these days. I have a 1-1/4" section of titanium line and a heavy duty swage fitting (also titanium) rated for 5,000+ psi. It's neat.
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Old 12-11-2011, 04:15:56 PM   #15
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Quote:
Originally Posted by Aceshigh
All of your AN fittings used today are "Army / Navy" spec fittings designed for aircraft back in the day made out of aluminum too.
I think they changed it to AN = Air Force / Navy these days though.

.
You should check out JIC fittings. They're the same as AN fittings with regard to flare degree (37 degrees) and thread size except they are more industrial/rugged looking instead of being anodized. They also typically come in a wider variety of adapters and can be had for better prices than AN fittings.
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