When do I need bigger fuel lines?

[DblTrbl]

Quote:

Originally Posted by iTurbo 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?

A small return line should not have this effect at boost.
At boost, most of the fuel is going into the engine and not being returned to the tank.
At idle most is being returned to the tank.

[phantomrt]

Well, a way to find out if the return line is too restrictive is to see what the wideband says if you unplug the vacuum line from the regulator. If the mixture leans out under full boost, with the vac line off, I don't think the return line would be the problem.

I had a problem of pegging my wideband richer than 10:1. Probably way richer. So, right now I have a check valve to prevent the regulator from seeing boost pressure. It just bleeds the pressure off, but keeps the vacuum sealed. I am right around 10.5:1 WOT right now. But I have a stock hi-torque ECU with +40 injectors and adjustable regulator. I Think my fuel pressure is somewhere around 23 PSI static. And I run rich with no pressure to the regulator.

[thedanielm]

Quote:

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

ya i guess i cant speak for everyone but stock my return line is smaller than the feed line,

and in theory fuel is used by the engine therefore there will never be more fuel returning to the tank than there is flowing to the rail.

[ACR Turtle]

Explains my L body dilemma. I have 90 psi at the rail with a Walbro and the Accufab adjusted all the way out to all the way in.
So if I run 5/16 or 3/8 supply then "theoretically" I should be able to get some adjustment? I was thinking of running 3/8 supply and using my supply as a return. I understand 3/8 is overkill (at least on my car) but I haven't found a continuous piece of 5/16 line.

[ACR Turtle]

I took the easy route. I ran 3/8 aluminum line as a return. AN fittings out of the regulator and BAM! 55 psi at the rail, then a little tweaking just right. I may take the left over 3/8 and run a supply line later on.

[John B]

Quote:

Originally Posted by Y2kTurtle I took the easy route. I ran 3/8 aluminum line as a return. AN fittings out of the regulator and BAM! 55 psi at the rail, then a little tweaking just right. I may take the left over 3/8 and run a supply line later on.

How much pressure does the return line have to hold? Is line strength an issue like with the supply line?

[turbovanman]

Quote:

Originally Posted by John B How much pressure does the return line have to hold? Is line strength an issue like with the supply line?

The return line should be able to hold maximum pump pressure in case the reg fails and you get full pressure going back to the tank. Don't kid yourself and say it won't happen, it does!

[John B]

Is there anything between the regulator and the tank? In other words, if I try to blow through the return line should I get a lot of resistance?

[turbovanman]

Quote:

Originally Posted by John B Is there anything between the regulator and the tank? In other words, if I try to blow through the return line should I get a lot of resistance?

No, you should be able to blow thru it but it might have a check valve on the end or something similiar.

[John B]

Hmmm, mine is REALLY hard to blow through, almost ruptured myself. I figured it was the weight of the residual fuel in the line, but now I wonder if it's blocked somehow. I guess I need to take the gas cap off and blow out the line with high pressure air. Thanks Simon.

[turbo minivan]

im am soon going to be running a second stock turbo pump and a second stock set of lines in my van and Y them together at the rail. thats how im making sure im not going to run out of fuel. safe? i guess we'll se how well i do it!

[Cracked]

Quote:

Originally Posted by iTurbo 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?

Yes, I figured this out with my afr, I had 52# injectors on a stock cal and wanted to go down to 28# , I could not go any lower thatn 37# with the 255 ltr/hr pump.So I went with the stock fuel pump and can go all the way down to 2#. I assume that the stock pump is about 130ltrs/hr So basically if i went with a larger return line I should be fine

[DblTrbl]

Quote:

Originally Posted by Cracked Yes, I figured this out with my afr, I had 52# injectors on a stock cal and wanted to go down to 28# , I could not go any lower thatn 37# with the 255 ltr/hr pump.So I went with the stock fuel pump and can go all the way down to 2#. I assume that the stock pump is about 130ltrs/hr So basically if i went with a larger return line I should be fine

I believe it has alot to do with the regulator rather than the fuel line. I have found that the regulators with the welded on retrn nipple flow less than the ones with the screw on fitting.

I'll bet if you hook the return line directly to the fuel feed line, with no regulator in between, you would get very low backpressure. Might be an interesting test.

Carl

[Ondonti]

Quote:

Originally Posted by Cracked Yes, I figured this out with my afr, I had 52# injectors on a stock cal and wanted to go down to 28# , I could not go any lower thatn 37# with the 255 ltr/hr pump.So I went with the stock fuel pump and can go all the way down to 2#. I assume that the stock pump is about 130ltrs/hr So basically if i went with a larger return line I should be fine

Put a bigger return line.

Just like a 3" exhaust helps even when you have a small turbo, the big line will help.

Im going to run into the same problem as you pretty soon.

Still, no one answered my question about some of the old carbed cars having 3/8 feed line. At that point, you can just start using your old feed line for return.

I guess autozone also loans out pipe benders to do your own.

[Putter]

I converted my Omni from carb to turbo, it was equipped with 5/16" lines when carbed.