When do I need bigger fuel lines?

[Pat]

Quote:

Originally Posted by TrboVan Can you explain that a little further? I am running big feed and a small return. (always have)

It only makes a difference if you can't get your rail fuel pressure down to where you need it to be.

[87GLHS465]

Quote:

Originally Posted by kedavis Your return line should always be the same size or one size larger than your feed line or your asking for pressure problems.

This only makes sence if your returing more fuel to the tank than your pulling out.

Clay

[TRRBOJEEP]

Quote:

Originally Posted by TrboVan Can you explain that a little further? I am running big feed and a small return. (always have)

Don't mean to but in, but I think Davis is just pointing out that a small return line may not be able to blead off enough fuel fast enough (if its being sent to the rail in a larger line) and the result could be an unwanted spike in your fuel psi.

It would have to be a pretty extreme case scenario thou I would imagine.

[kedavis]

Quote:

Originally Posted by TRRBOJEEP Don't mean to but in, but I think Davis is just pointing out that a small return line may not be able to blead off enough fuel fast enough (if its being sent to the rail in a larger line) and the result could be an unwanted spike in your fuel psi. It would have to be a pretty extreme case scenario thou I would imagine.

That is what I exactly what I mean as far as fuel line 5/16 is plenty of fuel line I think the problem a lot of people have with fuel issues is that some of the walbro high pressure pumps when you reach between 70 and 80 psi under boost they start to go into bypass you need to verify that your pump will hold a steady 85 psi if your going to 30 psi of boost if your pump starts to go into bypass at 75 then your otta luck you need to modify the bypass spring in your fuel pump to hold a steady 85 psi this is what the buick guys have been doing for years.

[Frank]

Interesting... that explains a few things I have seen on other cars.


Frank

[gasketmaster]

Quote:

Originally Posted by TrboVan Can you explain that a little further? I am running big feed and a small return. (always have)

It's really a concern more when you are idling or cruising......not really a concern at WOT for most.

Here is why:
A -8 fuel line will flow X amount of fuel at 45 psi. It is impossible for a smaller say -6 return line to return that same(or near same) amount of fuel back to the tank with an absense of pressure.Since the returned fuel should be coming into the "vented" tank "above" the level of fuel it should not be under pressure.
Fuel pressure regulators are pressure differencial devices.They only sense the difference in the incoming pressure and out going pressure(which there should be none in a vented return system).If your system is seeing pressure in the return side it effects the pressure numbers your are seeing on the rail side.

This problem is aggravated by larger fuel pumps like we tend to run on our performance vehicles ;)

[kedavis]

Quote:

Originally Posted by gasketmaster It's really a concern more when you are idling or cruising......not really a concern at WOT for most. Here is why: A -8 fuel line will flow X amount of fuel at 45 psi. It is impossible for a smaller say -6 return line to return that same(or near same) amount of fuel back to the tank with an absense of pressure.Since the returned fuel should be coming into the "vented" tank "above" the level of fuel it should not be under pressure. Fuel pressure regulators are pressure differencial devices.They only sense the difference in the incoming pressure out going pressure(which there should be none in a vented return system).If your system is seeing pressure in the return side it effects the pressure numbers your are seeing on the rail side. This problem is aggravated by larger fuel pumps like we tend to run on our performance vehicles ;)

Very good explanation I guess I should have explained myself better.

[DblTrbl]

Personally, I've seen more issues with the electrical supply to walbro pumps than tubing diameter. When a high performance pump is as running at 30 psi of boost, that means that the pump is seeing 85psi of fuel pressure and the electrical load (amps) is very, very high. High enough to overload the stock connector and wiring. I'd change the fuel pump wiring and fuel pump connector before I'd change the tubing. I've seen a 20 psi fuel pressure (maximum) increase changing my son's minivan fuel pump wiring.

Carl

[Mario_Boost]

There's a ton of great info in this thread. Thank you to all that contributed.

[Ondonti]

cant you find a 3/8 line on one of the old carbed cars?

[bullom]

Slight thread highjacking here -

What size are the factory return lines?
Are all turbo Dodge factory fuel supply lines 5/16"?

I need to replace the fuel hoses on my 90 turbo van. I started it up, smelled gas, and found gas spraying all over from one of the fuel filter hoses (yes - I will use high pressure fuel injection hose and high pressure fuel injection clamps ;)

Needless to say, its not moving till I get all the fuel hoses and clamps replaced from tank to engine and back again.

Brad Ullom
Fort Wayne, IN

[Reeves]

Do the carbed cars have 3/8" feed? I have a carbed car here that I am getting ready to junk...

[Heavytank2]

Heres a dumb question.... where do you buy fuel lines? LOL.

I mean, where can you buy it, what do they look like? Material? Can I buy it off a reel somewhere? Can I fab some?

[crazymadbastard]

Quote:

Originally Posted by Heavytank2 Heres a dumb question.... where do you buy fuel lines? LOL. I mean, where can you buy it, what do they look like? Material? Can I buy it off a reel somewhere? Can I fab some?

You can buy them from summitracing.com in aluminum , also locally at a parts store you can buy them with fittings/flares - these are all either aluminum or steel. Where the lines meet the regulator, there are rubber hose, these have to be rated for "fuel injection" ie high pressure.


PS
I also have a small return on my car it might be 3/16 id.

[iTurbo]

Quote:

Originally Posted by DblTrbl Personally, I've seen more issues with the electrical supply to walbro pumps than tubing diameter. When a high performance pump is as running at 30 psi of boost, that means that the pump is seeing 85psi of fuel pressure and the electrical load (amps) is very, very high. High enough to overload the stock connector and wiring. I'd change the fuel pump wiring and fuel pump connector before I'd change the tubing. I've seen a 20 psi fuel pressure (maximum) increase changing my son's minivan fuel pump wiring. Carl

I have had this happen on two vehicles already, both equipped with the Walbro 255 ltr/hr high pressure in-tank fuel pumps! On my Shelby Lancer and Shadow ES, it would start to cut out under boost and would run randomly then finally not run at all.

I found the (+) wire on the inside of the tank on the hangar assembly was burnt and corroded badly. The ground wire was fine. I had to fix it by purchasing a new fuel pump/hangar assembly. I reinstalled the Walbro pump in place of the new stock pump, and then upgraded to heavy gauge wire on the hangar, soldering the connections very well, and using a double layer of heat shrink tubing. Another thing that should help is the new fuel pump hangar I bought was for an '89 GTS, which directs fuel straight out the hangar instead of through the curly-Q hose that the '87 style hangar has.

Would this explain my overly rich wideband O2 curve that my Shelby Lancer has? It dynoed 196WHP/242WTQ on a Dynojet with 14 psi boost. It was using stock calibration, 804s, 3" exhaust. The wideband O2 curve dropped off the scale rich as soon as it went into boost all the way to redline. Same thing with my brother's TII '89 GTS which is similarly modded and has the Walbro 255 ltr/hr pump as well. I'm wondering if the stock fuel return line isn't flowing enough and causing rail pressures to rise too high in boost. Would upgrading the return line ease the load on the fuel pump?