I was asked to manufacture a 5 gallon tank for a customer building a BMW Mini race car, after discussions about size fittings baffling etc a fag packet sketch was produced in order to make the job.
I started with 1.5mm thick NS4 Aluminium sheet, plastic coated 1 side. Once dimensions were worked out I decided to complete as 2 pressed panels. Panels were marked out using tape measure, engineers square and fine tipped marker pen.
Once marked out the sheet was cut using a hydraulic guillotine for speed and accuracy, de-burring panels before proceeding reduces chance of cutting yourself whilst working with the sheet. Fold lines were marked on the panels but, before folding the strengthening swage lines needed to be put in – this I completed using a standard manual swaging machine, after which folding the 2 panels on a Box Pan Folder was completed. Results as shown –
Main body complete and ready for assembly, however I need to add filler hole, fuel pick up, return and breather hole, this will be completed in due course with a drill, hole saw and drill bits before tacking up.
Splash pan was manufactured again using 1.5mm NS4 aluminium and again marked out from sheet cut out using a guillotine and bench knife before pressing on the trusty box pan folder to the correct degree for the corners to meet up.
Once formed up to a square splash pan with a flat base I used a hole saw of 41mm diameter to cut a hole in the centre of the base for the filler neck to welds into. The filler neck was tig welded from the back of the into the base of the splash pan during welding the pan corners up, After welding the main body a drain stub was welded to the splash pan to drain away any spillage during topping the tank up.
Before assembling the tank, I used an electric hand drill to cut all holes in the tank body as required, this then means we can ensure a totally clean tank inside as we do not want swarf or aluminium dust inside the tank once complete for obvious reasons.
Tank foam was added to fill the tank to reduce fuel slosh before the 2 halves of the tank were assembled. Some adjustment was needed using clamps and small wedges to ensure that a neat outside corner joint was tacked up all round the edges to be joined by welding. If the set up is accurate a neater stronger weld can be produced and even penetration can be achieved, thus reducing chance of leaks or fractures. A good joint set up is also critical for speed of welding and aesthetics – e.g. weld will be a more even corner fillet if joint is tacked up correctly. So its worth spending a little for time and effort to get this part of the job right.
You will notice that I have already added fittings before set up of main tank body again to reduce chance of tank contamination. 
Using a coin tor score plastic coating reduces chance of scratching panel when removing plastic around areas that have to be welded. Aim is to leave as much plastic coating on the tank during manufacture to reduce scratch marks. Once complete it can all be removed.
Safety is a must when welding, you may have noticed in some images I have a fire extinguisher to hand should anything untoward happen, I wear TIG gloves and work overalls (fire retardant are best) and a quality air fed (& filtered welding helmet).
TIG welding produces a quality weld (dependant on welder skill, set up, gas flow, torch angle, torch aim etc), I aim for a nice even regular ripple effect and whilst welding tanks with outside corners a nice small “teardrop” effect in the bottom of the root, which tells me I am achieving a nice even bead of penetration – essential to ensure you get a strong, leak free joint.
Picture of completed tank, ready for pressure testing, which I do using a battery powered pneumatic pump, connected to one of the pipe stubs whilst blanking off the rest. Once under pressure ( a couple of bar is sufficient) the welded seams are brushed with soapy water whilst I look for a steady stream of small bubbles indicating a pin prick of a hole in the weld. As with all tank caps, aluminium or stainless steel it is a good idea to put a small amount of copper grease on the threads which helps prevent thread “pick up”.
Hope that this post may of been some help to you or at least an insight into building a race tank in aluminium.
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The biggest benefit of using fuel tank foam is to reduce fuel “sloshing” in the tank. Tank foam is special open cell foam that cushions the fuel sloshing around in the tank and reduces fuel moving about. This “sloshing” can cause a change in the centre of gravity of the car or vehicle, motorcycles can be affected far more by fuel sloshing, due to sheer weight of fuel moving around (approx 1 ltr = 1kg). Adding foam also reduces the chance of injected engines being starved of fuel during long corners as the fuel tries to slosh to one side. The foam only takes up approx 3-4% volume of the tank, so tank capacity is not drasticall affected. Tank foam can be purchased in 1 cut piece to fit into a new tank or alternatively small blocks that can be squashed and pushed in through the filler neck or sender aperture (if available). A point to consider is that tank foam is not always sufficient to use in fuel tanks for drift cars as forces and speed involved in changing direction so quickly can still cause fuel starvation if the fuel moves around the tank too much. In this case hinged or pivoting baffles are needed instead of tank foam. These work by closing off an area of the tank and keeping fuel in a position where the fuel pick up can do just that – pick it up to feed the fuel pump. When the car direction changes the hinged baffle opens to allow fuel to flow back into the chamber. Alternative methods are utilising a fuel swirl pot as an integral part of the tank or between the low and high pressure pumps to maintain constant feed to the injectors. This is not a requirement or so much of a problem on vehicles that run on carbs as they have a dash pot in which fuel is kept at a constant level by the float and shut off valve.
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