Converting to returnless fuel system?

[Schmieder]

So I hear it is possible to run a twin pump and line one pump through the feed port on the fuel rail and line the other pump to the return port on the fuel rail.

Essentially allowing twice as much flow to the rails under higher pressure. Using HP Tuner the injector flow rate can be properly adjusted across the vacuum range in the intake plenum.

And if being returnless creates a negative side effect negating the conversion, why not tap the Schrader Valve for the return port to the fuel tank. Plumbing all this isn't too hard or incredibly expensive. And powering two fuel pumps is also a very simple task, just another relay triggered by the same fuel pump circuit.

Well, the twin pumps would need to be external. But again, not too hard to do.

If heat is an issue, there are great heat shielding materials that would be economical. Only shielding small fuel lines.

I think I'm onto an interesting idea here. This could really benefit higher boosted applications. Like 30+ psi....who can argue more pressure, twice the pumping power and double the flow into the rail?

[robertisaar]

.......... yes, i can see this providing significantly higher amounts of fuel, but it would make the fuel pressure regulator entirely useless i would think..... and i can't think of a way to accurately tell the PCM what the fuel pressure(and therefore flow capability) actually is without a fuel pressure sensor because the pumps likely won't generate the same amount of pressure at all times.... IIRC, GM didn't use them even in most OBD2 applications?

i'd also think it would hard on the pumps?

[Schmieder]

Unless the pumps were accurate or a pressure equalizer were incorporated some how. But then, like you said, we would need an FPR to keep the PCM happy.

Big question is if the Schrader Valve can flow enough to support the FPR. Move the FPR to the Shrader Valve and then have two feed lines to the fuel rails, -6AN Braided Stainless lines of course. An adjustable FPR would be perfect to retune the proper/desired fuel pressure.

I bet a check valve in each feed line would be a good idea since both pumps may put pressure on each other. Twin Walbro High Pressure pumps should handle the abuse of a modest fuel rail psi. Maybe push the same fuel pressure as the 3800's.

This idea seems quite feasable and not to expensive. A bit of cost but nothing like digging really deep for such drastic conversions.

[pocket-rocket]

I think the big problem treating the schrader as the return line would be the very small volume of fuel it would pass- not near enough to use as a return reliably. Also, I've read that some returnless use variable fuel pumps controlled by the PCM to up and down the fuel pressure. Running a FPR at the tank would be an option, but then the length of vacuum hose from the bay to the tank would make that interesting as far as a reliable signal went.

[Barry]

^ Good point on the length of the line effecting things, however, it wont. Assuming no kinks and proper hose is used there will be no noticeable lag in the system

[AleroB888]

You could just get one higher capacity pump, configure the lines like this:

[Schmieder]

You could just get one higher capacity pump, configure the lines like this:

That is a beautiful build.

Yes, a walbro high pressure/high flow with larger fuel lines would also be effective.

I bet the fuel pumps could be controlled via voltage adjustments, just as long as the amps remain stable. Using a vacuum triggered resistor of some sort maybe. An electronic VacFPR. But that is getting a little tricky to do with a stock PCM. At that point, I think going Megasquirt would be a better option first.

[CNCguy]

I think trying to control two pumps would really complicate things. It would be cheaper and simpler to use a single large pump, external regulator and lines feeding each side of the fuel rail. A setup like this is easy to do and works well.

[AleroB888]

I think trying to control two pumps would really complicate things. It would be cheaper and simpler to use a single large pump, external regulator and lines feeding each side of the fuel rail. A setup like this is easy to do and works well.

And I must give you credit for steering me in that direction, works great so far.

One other thing not often considered is the fuel tank venting when other upgrades are made. The Aeromotive people say it becomes a factor.

[pocket-rocket]

^ Good point on the length of the line effecting things, however, it wont. Assuming no kinks and proper hose is used there will be no noticeable lag in the system

When installing a boost controller in a turbo vehicle they recommend the shortest vacuum hose possible, and I recall the term brake lag when in truck driving school. I'm not saying that it would damage something from a lean condition, but knowing air brakes in a truck aren't pin-point responsive like hydraulic brakes in a car, I believe there would be some lag there. .1 seconds is enough to send an engine lean, so I would want to test how fast the system reacts before using the FPR at the tank.

[Schmieder]

When installing a boost controller in a turbo vehicle they recommend the shortest vacuum hose possible, and I recall the term brake lag when in truck driving school. I'm not saying that it would damage something from a lean condition, but knowing air brakes in a truck aren't pin-point responsive like hydraulic brakes in a car, I believe there would be some lag there. .1 seconds is enough to send an engine lean, so I would want to test how fast the system reacts before using the FPR at the tank.

Good point about the MBC.

I think trying to control two pumps would really complicate things. It would be cheaper and simpler to use a single large pump, external regulator and lines feeding each side of the fuel rail. A setup like this is easy to do and works well.

I like the Mallory Lines graphic posted, that seems to be the most effective and simplest method for dual feeds into the fuel rail.

Atm, I'm just plumbing a new intake line so I can rig my fuel pressure gauge sensor. It is going to be data log only but that's just fine. Having the Fuel Pressure logged with the wideband, and everything else, will really help for an accurate tune. But now I know to rig the sensor where the Mallory System would connect, so I'm prepared to switch over later in time. After a few years, I hope to have the fastest 96 Grand Prix while not sacrificing comfort and style.