Custom fuel setup question

**asshanson** · 02-25-2013

I know this isn't mitsu related, but fuel systems are pretty universal, just think of this as a fuel cell. Here is a pic of the fuel system on my car as it sits today:

Right now the tank has two AN bungs on the bottom left side of the tank, one for the feed line and one for the return.

My first question is, can you have the pump after the filter? Someone told me the filter should always be after the pump, something about not having too much restriction on the inlet of the pump.

Next, the main problem with this setup is the tank is internally divided into two sections, the right 1/3 of the tank is completely separate with a few check valves that allow fuel to flow into that side, but not back into the other side. So basically with this setup there is about 2-3 gallons on the side where the OEM sending unit is (nothing hooked up there), and I can never access that fuel because it's pulling from the other side.

I have a few options that I've been considering, but I don't know enough about fuel pumps and fluid dynamics to know if it will will introduce problems.

1st solution: add a fuel pump in the stock location and Y into the feed line after the other pump. The drawback is I think the right side of the tank might empty first sine the return is going to the left side. I know there are the valves that allow fuel to flow back into the right side, but they just work on gravity and I'm not sure they can support the amount of flow that the fuel pump is putting out. So basically the left side would fill up faster than it can drain to the right side, and the right side pump would be running dry and burn out or something. Plus if it's putting out air I'm not sure how that would affect fuel pressure at the point it runs dry, there might be a drop in pressure for a second. Does that make sense?

2nd solution: weld in a bung to the right side of the tank, and Y the line right before the filter, so that the existing pump would be pulling from both sides of the tank. Again my question is what happens when the right side is empty, and the pump pulls from a full line and an empty line simultaneously? Does air get introduced, or will it just pull the fuel from the full line?

Hope this makes sense, basically you have to think of it as two separate tanks since one side could go empty before the other. I can draw pics of solutions 1 and 2 if it will make more sense.

**Shane@DBPerformance** · 02-25-2013

Is this an aftermarket setup? 2G DSMs, Evos, GT500 have split saddle tank setups that require a siphon effect from the factory return/fuel pump assembly to get fuel from the other side to the fuel pump. I wouldn't run a setup that would pull from two different lines/locations.

**asshanson** · 02-25-2013

Here is the product, there are a few pictures. Basically the tank is divided into two sections.
http://www.proalloy.co.uk/cgi-bin/si...84&id=proalloy

Yes it's totally aftermarket/custom. The stock setup is a returnless feed from the right side of the tank, but since it's a wide tank the cars fuel starve on long turns. Which is why I thought to have two gravity feed lines, one from each side of the tank.

So it could be potentially dangerous to pull from two gravity fed lines? One from each side of the tank? I really don't want to switch to the stock setup, but maybe I should just do that and plug the two AN bungs on the left side of the tank.

EclipseGST · 02-25-2013

I dont like how the feed is on the side of the tank. It should be on the rear of the tank, in the middle and lower than the bottom of the tank in my opinion.

Take a right turn with that tank and all the fuel will rush to the left of it if too low, it will start sucking air.

This is how I've always thought was the best idea. The feed line outlets on the bottom face the rear of the car, return line in the top of the tank.

**asshanson** · 02-26-2013

Ok I made some better drawings to help visualize how this aftermarket tank works, these drawings are with a view from the rear of the car. I think I understand the risks of having a single pump pull from two areas, if one side went dry it would suck in both air and fuel and could have bad results.

Here is the existing setup, I think the person who did this setup had the right idea, they just put the pump on the wrong side of the tank. The driver's side has the check valves so fuel can enter that side but not come out. I believe this is why my fuel gauge always reads full no matter what, because that area got full and can never be emptied from the right side.

Here is proposed solution 1. It retains the sump setup with external pump and filter, but it pulls from the rear center portion of the baffled area, and returns to the same section. Don't mind the reverse fuel flow, I just did that for ease of drawing.

Here is solution 2. It puts an internal pump in the OEM location (without the internal regulator), and the return line is plumbed back into the baffled location.

Are there any benefits to running an external sump pump vs an internal pump? The only difference in labor is having to weld an extra bung but that is trivial since I need one for the return anyway. I have the hardware for the sump setup but an internal 255 is cheap.

Thoughts?

EclipseGST · 02-26-2013

Either solution would work but I dont like how the return goes into the bottom of the tank, I feel there would be constant resistance creating fuel pressure to be higher at the rail.

I would honestly use the factory housing and put a walbro 255 or similar in it like a dsm but thats just me. Either setup would work.

**asshanson** · 02-26-2013

There is one outlet on the factory housing, so I can't use a return setup if I put a pump in the stock location unless the return is plumbed to the bottom of the tank. I see what you mean about resistance though, might create some back pressure in the return line. When this is all done I will definitely verify pressure with a gauge.

The upper part of the tank is wedged into the frame so only the bottom area is accessible. Maybe I could sump for the feed and put the return into the stock line on the top. I'll have a better idea what is possible once I drop the tank. Thanks for the input so far.

EclipseGST · 02-26-2013

Yeah, with the return in the bottom of the tank, I would assume it would put more stress and resistance on the pump as well. Just a thought.

**asshanson** · 03-04-2013

Well I feel stupid. This is apparently the top of the line Pro Alloy tank, and instead of using the OEM fuel sending location, there is an internally baffled center collector, with internal pipes that run to the side of the tank where they are AN fittings.

I emailed the manufacturer to see how I can go about getting a fuel level gauge hooked up since there is no room for the stock one, but everything else will be going back in exactly how it was before. I feel stupid, waste of about 5 hours to get it all out, hopefully not more than a couple hours to put it all back in.

EclipseGST · 03-04-2013

Why feel stupid? You didnt know, you were being smart by looking into it instead of just "chancing" it. Glad it worked out and you didnt have to modify anything!

A//// Guy · 03-04-2013

Yea glad you found out what kind of tank it is actually!