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I need to fabricate a gas tank that straddles the driveshaft tunnel. This means I'll have two tanks on each side of the tunnel, joined by a connecting section on top. I want to make both sides drop down to keep the weight low in the car. I'd rather not run a pump in each tank, as I am already going to feed a swirl pot with an external pump, and think three pumps might be a bit much!

I was considering a hard line connecting the bottom of each tank. It wouid pass under the driveshaft. If I had the tank opposite the fuel pump maybe 0.5" higher than the tank containing the fuel pump, it might work. A bit weird, but I've seen it in some cars, and might be the easiest solution to my dilemma.
Any suggestions would be welcome!

I"d be worried about a flailing drive shaft end. ..
Perhaps a braided line (flexible so it has some ability to absorb deformation without rupturing and a metal sheath to absorb sharp edges)?

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"There are times when a broken tool is better than a sound one, or a twisted personality more useful than a whole one.
For instance, a whole beer bottle isn't half the weapon that half a beer bottle is ..." Randall Garrett

At one point when I was designing my own chassis, I considered a 2-part tank. I didn't have the issue of dealing with the driveshaft, however. Two things I decided on for the design was: 1) a sump to collect junk (which you can't truly avoid) in the fuel before the fuel filter; and 2) connecting one tank part to the other with a tube/pipe down low and large enough to allow one tank to fill from the other. That is, one filler for both tank parts. You will still need a breather from the part without the filler to allow air to escape as it fills from the first part. My plan was to join the top of the part without the filler to the filler tube on the other and allow it to breathe with the tank part having the filler tube/cap.

I hope this is helpful.

Cheers,

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886

Check your state regs to ensure that this won't ring alarm bells. Maybe NY is one of the free-wheeling ones, but I believe current construction regs for production passenger cars, whether in US or Canada, do not allow bottom feed from gas tanks.

The safer solution for this, albeit not the cheap one, is to use twin pumps, or .... a Y'd pick-up to a single external pump through top-mounted conections. The pump will always draw preferencially from the side of the tank with higher head and thus maintain the two sides at similar levels when they get below the connecting 'bridge'. As an aside, this tank design would reduce sloshing issues.

Years ago we re-used a bottom feed tank (in the days when it was OK for manufacturers to use them). It ultimately leaked at the fitting, and unfortunately we had reused it in a boat .... Fortunately, the smell was noticed before anyone did anything involving an ignition key!

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Warren
Isuzu Pickup/SR20DE, +401 COLD frame
Build Log: viewtopic.php?f=35&t=11601

That is an intriguing suggestion. In this case, the pickups in each of the (connected) tanks would be a tube that ran from the top to a pickup at the bottom, and at the top each pickup would have a fuel line running to a "T", which would then connect to the first pump? This would then feed the swirl pot, which would have a second pump upstream to send gas to the engine.

My 89 Golf had this setup. You had a high-volume, low pressure pump in the fuel tank, which pumped fuel to a little "Box" under the rear passenger foot well. In that little box was a high pressure, lower volume pump that fed the injectors. I'm not sure of the specs on that setup, but betting that it would work for most 4- and 6-cylinder engines.

Added bonus was that VW did it "right" -- you can simply remove a plate (3, #2 phillips screws holding it in, usually rusted a bit) that is located in the trunk/hatch under the carpet, and then remove the in-tank pump within minutes. The ring operated like an old mason canning jar ring. Too bad GM didn't do it that way, and caused hundreds of thousands of expensive repairs when its cars required that the fuel tank be dropped to do a job that an amateur could do in minutes in the VW.

That little "Box" can be removed in minutes too, if you're not real picky about how you remove hose clamps and some screws that might be rusted.

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Geek49203 aka
Tim Wohlford
Louisville, KY
Hayes front, S10 +2 rear, Lalo body.

No one else??
The transfer pump, that is sucking from both chambers, will stop pumping as soon as it sucks air from the low/empty chamber. It will not start pumping again until both pickups are covered with fuel and the pump has a chance to prime itself again. This time period may be so long that the high pressure pump runs dry and the engine sputters/dies. Running the high pressure pump dry can also damage it.
There are siphon jet pumps from some manufactures that bleed some high pressure fuel to create vacuum that is used to transfer fuel. May be hard to adapt to a new tank. I think either Cheapracer or Miatav8 have mentioned it in another log (hope I am giving proper credit).
I added a turbo to a 1978 BMW 320I and had fuel starvation problems when cornering. The 320I has 2 interconnected fuel tanks but only one lift pump inside of the right tank. I found the high volume lift pump had failed and a crack in the connecting hose on the pressure side of the pump, inside of the tank, was allowing air to be sucked into the fuel system. I bypassed the high volume pump with a new longer piece of hose without any further problems.
I would recommend a small pulse pump (that can run dry without a problem) to transfer fuel from one side of the tank to the other. I would draw fuel with the high pressure pump from the side being filled by the pulse pump. I would also return fuel to the filled side. This can all be done from the top of the tank if need be.
I have 2 separate tanks in the Wycked 7, with a crossover pipe at the bottom, vent pipes at the top and some interesting baffles. I only use the one Toyota MR2 fuel pump/level sender that was from the donor. The fuel filler is only on the left tank.
The only hose actually hooked up is the crossover hose between the tanks

JMR

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My build log viewtopic.php?f=36&t=10658&start=0 NOW NAMED =The Wycked 7

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Could you just use one larger tank (higher) in the passenger side of the car as this will also help with ballast to counter your weight in the driver seat. Sometimes the simplest solution is the best.

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2015 & 2016 EMod Florida State Autocross Champion
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Kartracer,

It's hard to believe, eh? (said the Canuck)

A pump's flow rate is reduced as it works against increased head betwen inlet and outlet. Consequently, when drawing from two tanks with different levels to feed a common outlet, the flow rate will be greater from the tank with the higher level. The tanks don't need to be of exactly the same volume, but the whole concept falls apart when the bottoms of the tanks are at different levels, in which case the tank with the higher bottom will ultimately run dry and you will lose prime.

I run my domestic water supply with a single pump drawing from two cisterns. I long ago gave up managing water levels with the valves at the top of the tanks, and now let hydraulic head look after it.

Your own approach shows that idicker's proposal will work, and I suppose that two more joints won't matter in the scheme of things, with all the other connectors in the fuel system. As long as the inspector doesn't care, or can't see it.

I'll go back under my rock!

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Warren
Isuzu Pickup/SR20DE, +401 COLD frame
Build Log: viewtopic.php?f=35&t=11601

Someone here, in the last year or so, posted about a device that went on the pickup tubes. Presumably if it was wet, it allowed fuel to pass. If it was dry, then it would shut off the pickup tube allowing the common pump to draw from the filled side. I think the post was someting to do with using 2 corner pickup tubes, eliminating the need for baffles. I can't find it right now. This would not require the crossover tube from below.

It is hard to argue with success that kartracer had. the crossover tube would have to be larger than 1/4" so that filling would not be delayed as the fuel level balanced between the two. The smaller tanks would be better for cornering; sort of a built in baffle, if you will. Even better if the bottoms were sharply "V" shaped.

Alternatively, to avoid the low crossover pipe, you might use one side as normal tank and the 2nd side as a "reserve" tank. Put a fuel level sensor in both sides with a low pressure pump to pump from the reserve into the normal tank. Now build an electronic comparator that compares the fuel level of the two. shouldn't be too difficult. As the fuel in the normal tank is consumed, the comparator automatically pumps fuel in from the reserve to maintain near equal levels then shuts off. Since you intend to straddle the tunnel, you would not need two fuel filler caps, vents etc.

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Chuck.

“Any suspension will work if you don’t let it.” - Colin Chapman

Visit my ongoing MGB Rustoration log: over HERE

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Thanks for all the great suggestions. The goal was to get the tank and all it's weight low in the car. I like the idea of a transfer pump. But you know, at this point I should probably just pony up the cash and run two pumps, one in each tank.

While perusing the internet, I came across a nice fuel pickup from Walbro that must have a check valve of some sort, because they claim when the pickup is dry it will no longer flow gas, thus keeping air out of the fuel pump. I thought someone else might find this link useful:
http://www.liquidironindustries.com/product.php?productid=17581&cat=273&page=1

Any suggestions for what metal to make the tank out of? Seems to come down to thicker aluminum vs thinner stainless.

Make it easy on yourself. Plain steel. Coat the inside with RedKote.

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Chuck.

“Any suspension will work if you don’t let it.” - Colin Chapman

Visit my ongoing MGB Rustoration log: over HERE

Or my Wankel powered Locost log : over HERE

And don't forget my Cushman Truckster resto Locostusa.com/forums/viewtopic.php?f=36&t=17766

Warren, you are absolutely correct - for a stationary object. I would also assume that the levels of the cisterns are never drawn down enough to uncover the pickups and if they are, it would not be noticeable due to a pressure tank in the system?
A moving vehicle is quite different especially if spirited driving is involved.

JMR

Made mine from 1/4" aluminum for the sides and top for the safety factor, the bottom is 1/8" with a sump to draw from at the rear of the car. The theory is that if there is a severe enough accident to rupture the tank the bottom will be the weak link and the passengers won't be soaked in fuel .
Also it makes it much easier to service and with a few baffles it will not mess with your weight balance, the filler neck is at the rear and won't be bothered by a spare tire.(The theory about the bottom is so far untested , I hope it remains so.)

Stainless is far heavier and harder to service (weld) if need be .But to each his own .............

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