aluminum tank question

[Jim Rosenthal]

Having found templates for the fuel tanks, I think I am going to try to get aluminum tanks made up for the GT40. Some questions, since these will more than likely get made by the metalworking shop that is doing most of these custom parts:

-what are aluminum tanks made of- what alloy, and how thick?

-where do the baffles get placed? are there baffles around the sender?

-the tank would need a fill, an opening for the sender, a fitting and downpipe for the fuel pump suction line, and a vent- anything else?

-where does the vent get vented to?

-we're going to try to do without the foam that goes inside fuel cells, since my understanding is that it degrades faster than ever with alcohol mixed fuels...and when it degrades, it ends up in the fuel system.

I don't think I can get plastic tanks made up at a reasonable price. I'm satisfied that aluminum tanks will be okay if they are kept clean, and that water is kept out of the fuel. This application is not the same as a boat, where I wouldn't have aluminum tanks on a bet.

Clearly I know nothing about all this, so any advice is appreciated.

 

[Cliff Beer]

Hi Jim, maybe check out some of the information and possibilities at Fuel Safe if you haven't had a look there already (www.fuelsafe.com). They can do custom tanks with bladders - but it's not inexpensive, unfortunately. The bladder will save the ally tank if any water does get in there, despite best efforts to keep it out. Anyway, some good information there. Good luck!

 

[Dimi Terleckyj]

Hi Jim

For a number of reasons I had my fuel tanks made from stainless which I feel is the only material strong enough and resistant to corrosion and fuel mixes and additives.

It is also easy to work weld and shape to suit your needs.

Having mine made from stainless means I dont have to worry about that part of my car especially given the volatile nature of it's contents and where the tanks are fitted in a 40.

Dimi.

 

[Trevor Booth]

Jim,
stainless would not be my material of choice, stainless work hardens and unless totally isolated from any torsional loading there may be an issue with work hardening leading to failure. There is nothing wrong with aluminium. It is very forgiving and I might suggest is more crashworthy than stainless. A foam filled side tank on a 40 would not necessarily need baffles, however, a one way gated well at the rear of the tank in which the pickup is located is recommended.

I also suggest that the tanks are allowed to "float" in the side pods of the car and reatined/located by a resilient material. ie meduim density rubber. Cork blocks also work very well. Allow the tank to sit in say 4 "saddles" for support

In terms of venting you will need a fill vent which in normal circumstances comes from the rear of the tank to the filler neck, the vent should be positioned so that you get approx 95 % fill leaving room for exansion of the fuel.

In terms of a free vent to let air in as you draw down the fuel will depend on emission requirements. In todays vehicles the free vent returns to a carbon cannister which in turn is connected to the inlet manifold. This collects evaporative emissions. In the event that emission requirement is not an issue then the free vent can be located any where, It is recommended that it be reasonably high on the car to prevent spillage.

A free vent located in the filler cap will perform Ok , however, if the car turns over fuel will escape. In a frontal impact the free vent will allow fuel to escape.

I would run a free vent from the rear of the tank, up the engine bay bulkhead as far as possible then return to at least the lowest part of the fuel tank. Not terribly original but reasonably safe. I would not have free vents in the filler cap.
The other altrenative is to get a rollover vent from a hiway truck (tractor) fuel tank. This has a ball in it that closes the fee vent in the event of a rollover.
A small fuel filter on the free vent will stop dust and dirt getting in as the fuel expands and contracts and air is drawn is as you draw down the fuel.

In terms of foam compatibilty, I would check with the manufacturers.
With the srewdriver handle melting fuel that we get here we have had no foam issues.
Given the location of tanks on a 40 a foam filled tank is a loooooooooong way safer than a baffled and non foam filled.
The purpose of the foam is to allow the fuel to burn off safely in the event of tank rupture, this it does by encapsulating the fuel "within the foam"
Say you get a tank rupture and fuel spillage on the ground or hot parts of the car, If you get a fire it will burn the spillage as far back as the tank and it will then burn on the surface of the foam.

With a non foam tank and it gets ruptured and fuel spillage as a result, any fire is very neatly directed back to the scene of the explosion -- the by now part empty tank

thickness - 1.5 - 2.0 mm is normally satisfactory. alloy 5005 "quarter hard" would be a reasonable choice.

Water in the fuel, not an issue as far as aluminium concerned. keep your tanks full and minimise the condensation, a dose of methylated sprits now and then will absorb any water.

hope this helps

 

[Trevor Booth]

Jim,
stainless would not be my material of choice, stainless work hardens and unless totally isolated from any torsional loading there may be an issue with work hardening leading to failure. There is nothing wrong with aluminium. It is very forgiving and I might suggest is more crashworthy than stainless. A foam filled side tank on a 40 would not necessarily need baffles, however, a one way gated well at the rear of the tank in which the pickup is loacted is recommended.

I also suggest that the tanks are allowed to "float" in the side pods of the car and reatined/located by a resilient material. ie meduim density rubber. Cork blocks also work very well. Allow the tank to sit in say 4 "saddles" for support

In terms of venting you will need a fill vent which in normal circumstances comes from the back of the tank to the filler neck, the vent should be positioned so that you get approx 95 % fill leaving room for exansion of the fuel.

In terms of a free vent to let air in as you draw down the fuel will depend on emission requirements. In todays vehicles the free vent returns to a carbon cannister which in tern is connected to the inlet manifold. This collects evaporative emissions. In the event that emission requirement is not an issue then the free vent can be located any where, It is recommended that it be reasonably high on the car to prevent spillage.

A free vent located in the filler cap will perform Ok , however, if the car turns over fuel will escape. In a frontal impact the free vent will allow fuel to escape.

I would run a free vent from the rear of the tank, up the engine bay bulkhead as far as possible then return to at least the lowest part of the fuel tank. Not terribly original but reasonably safe. I would not have free vents in the filler cap.
The other altrenative is to get a rollover vent from a hiway truck (tractor) fuel tank. This has a ball in it that closes the fee vent in the event of a rollover.
A small fuel filter on the free vent will stop dust and dirt getting in as the fuel expands and contracts and air is drawn is as you draw down the fuel.

In terms of foam compatibilty, I would check with the manufacturers.
With the srewdriver handle melting fuel that we get here we have had no foam issues.
Given the location of tanks on a 40 a foam filled tank is a loooooooooong way safer than a baffled and non foam filled.
The purpose of the foam is to allow the fuel to burn off safely in the event of tank rupture, this it does by encapsulating the fuel "within the foam"
Say you get a tank rupture and fuel spillage on the ground or hot parts of the car, If you get a fire it will burn the spillage as far back as the tank and it will then burn on the surface of the foam.

With a non foam tank and it gets ruptured and fuel spillage as a result, any fire is very neatly directed back to the scene of the explosion -- the by now part empty tank

thickness - 1.5 - 2.0 mm is normally satisfactory. alloy 5005 "quarter hard" would be a reasonable choice.

Water in the fuel, not an issue as far as aluminium concerned. keep your tanks full and minimise the condensation, a dose of methylated sprits now and then will absorb any water.

hope this helps

 

[Trevor Booth]

two posts at the one time, must be one for each tank

 

[egoman/ Shawn Wedge]

Actually aluminum also work hardens, and it may even be more prone to it than stainless.

 

[Terry Oxandale]

Are there any successful coatings availabe that the home builder can use to protect the interior aluminum walls from ethanol's effects (for application while tanks are still "virgin")?

 

[Jim Rosenthal]

Much appreciated, Trevor. Although I have to confess I only read one of the posts, so I can only build one tank .

POR-15 sells a fuel tank coating that I'd use to coat the interior of the tank. The information on how to vent the tank is also much appreciated. I think vintage GT40s had the tanks vented into the fuel filler, as I recall at least one photo of one in flames after fuel climbed up the filler pipe and caught fire. I don't think I want that to happen, do I.

 

[Ron Earp]

Are there any successful coatings availabe that the home builder can use to protect the interior aluminum walls from ethanol's effects (for application while tanks are still "virgin")?

You could have the tanks anodized a color, or even clear. That will protect it and it isn't very expensive.

 

[Jim Rosenthal]

A good idea, actually. There is a company that does hard-coat anodizing up in Baltimore, which I'd forgotten about. Can a part that is the shape of a tank, but that isn't a closed vessel, such as a tank with openings, be anodized?

 

[Jack]

Yes Jim it can. The best aluminum fuel tank material would be 5052 T-6.
The POR-15 product is great for coating inside, as is the Rust Bullet product.

Much cheaper than anodizing and just as effective. Usually, no inside coating is really needed for 5052 T-6 because the surface grain is tighter and harder. IMO of course..

 

[Cliff Beer]

I can't imagine that either ss or aluminum would work harden when configured in tank. A properly designed fuel tank doesn't flex overall, nor flex significantly on any face. If they're built right, internal baffles contribute to the structural integrity of the tank, for example.

In other words, if your ss/alloy tank is flexing enough to work harden and thereby create a possibility of cracking, then your tank needs to be better designed.....

Copper works pretty well but needs structural support as it's really too soft for unsupported spans or more than about 12-14 inches, even in fairly heavy gauge.

 

[Jim Rosenthal]

Right, and this is all quite useful. I am going to talk to Metalcrafts tomorrow about these.

We're talking about two tanks, each about forty inches long (seemed like a good number, right?), and the external shape is about 8x11 inches in "greatest dimensions", as the pathologists say. The two tanks can be made the same, but one will go more or less to the back of the sponson area, where the battery resides, and the other will have some space behind it. I'm also going to ask them to weld a tab or two to the tank near the front, so it can be bolted to one of the ribs- the foremost one. Between that and some neoprene strips padding the flat faces of the tank, it should fit in there snugly.

I have to look at the original drawings and see how all the plumbing is hooked up. Access to these tanks is not easy, and is even more difficult with a rigid tank such as this. I am hoping to group all the holes into only two areas- one at the front, where the fill is going to be, and one right underneath the access plate which is on the top of the sponson. If I can get the fuel tap, the vent fitting, and the sender all into that area, I'll be very happy.

 

[Phil]

JIm:
I have made quite a few tanks, and mostly aluminum. I use 5052 alloy, which is a non hardening and very malleable grade.
I would suggest a couple of things.
Mount the tanks with a strap underneath, tabs tend to crack from the local loading, and flexing. Aluminum can expand or contract as much as 1/8" per foot with large temperature changes, You wont see this much, but you may see enough movement to break a weld.
Use some type of rubber under the strap, not foam material as it will hold moisture and could corrode the tank. Also you may want to weld a piece wider than the strap around the tank as a sacrificer.
Baffles can be 2 or 3 partitions inside the tank with small notches at the bottom, they will do a good job...just leave room for your sender.
Have your fabricator put a couple of extra bungs on the tank, easy at time of fabbing, and also a drain.
A good guage is .080, sturdy enough and easier to weld seams than thinner material. Your fabricator will know how to assemble the seams to maintain integrity.
Hope some of this helps.
Cheers
Phil

 

[Jack]

Good advice from Phil.
I use 60-70 durometer neoprene strips (about 3/16" thick) underneath the tank as well as on the mounting tabs. This isolates the tank electrically, so use a ground wire from the sending unit (NEG) and route to a mounting bolt of the filler cap. Less than one-ohm resistance is acceptable and will also prevent a static discharge.
.080 -.120 material thickness for tanks of less than 25 gallons capacity is very sufficient.

 

[Jim Rosenthal]

Got it. The mounting problem is that something needs to secure the tanks down, and it is hard to get to those areas to strap them down. I'll look at it again and see what I can get in there with. I thought the tab idea would work if the tanks weren't moving around, but I agree the vibration might break the tab off, and if it did, the tank might leak. I'll figure out something else.

I think RCI etc sell fills made up, which maybe I can get from them. Or Pegasus, or someone. Any suggestions on how to set up the pickup tube, and how big it has to be? I figured a 4-AN line for the vent would be large enough, what do you all think?

 

[Phil]

Jim:
I usually make the pickup from a piece of 1 1/4 alum rod. leave the top full size and step it down so it will fit into the tank, usually 7/8. You can then drill the top and thread it for your fitting, drill the bottom and weld in a 1/2" tube that goes down to about 1/4" off the bottom of the tank. You can also make a larger bung and thread the whole pickup assy. into it.
Also, the Neoprene straps Moeller is talking about work well. Stop by any truck dealer and they will have neoprene that is shaped like a shallow U, it fits over the strap and stays put.
I mounted my tanks this way, and used 2 stainless straps on each one.
A small piece of screen material on the bottom of the pickup may be useful to stop small particles from entering the fuel system.
Good Luck
Phil

 

[Trevor Booth]

Jim ,
you have a lot of good information there. I understand your chassis started life as a DB unit. It should have a series of internal ribs in the sponsons as the original units. The bag tanks were formed to go around the ribs giving max volume. With an aluminium tank you are limited by the internal dimensions of the ribs.
What I did was to make the tank slightly smaller than the internal ribs, I then coated the inside face of the ribs with a rubberised polyurethane. I built this up with succesive coats to about 1mm thick. The tank then slides in from the front and rests on the rubberised coating. I used a cork block at both ends to minimise for and aft movement.
basically the tank is just sitting in the sponson and free to move, no bolts , no straps, no tabs , nothing to come loose and cause a problem. Just imagine a nut coming off a bracket holding the tank , ratling around in the sponson getting caught somewhere and rupturing the tank.
The car has done two Tarmac Rallies in Targa Tasmania, a VERY tough event, lots of race meetings, an impact with tree (low speed) and NO problems with fuel tanks.

 

[Jim Rosenthal]

Right- the bag tanks were made to go in between the ribs on the sides and top, I think, although they had blocks under them to take up the bottom areas- I think the floors of the bag tanks were fairly flat. (I also have heard that they used to collapse the bag tanks with a shop vacuum, and then push the rubber bag into the sponson with a broomstick- pretty high tech.)

I do have a DB chassis and the construction is as you've described. We'll figure out some way to pad the faces of the tanks against the insides of the sponson ribs, so that things don't float around in there; that should do, by your account.

Thanks to all for the help, and all the knowledge that it would have taken me ages to figure out on my own, assuming I could even do it. When I finally finish my car and drive it around, I will think often of all the help I've gotten here, solving all these problems.