Fuel supply: Tanks and safety

Safety aspects of the fuel supply

On the GT40, the position of the tanks is predetermined by the original design – they are located in the voluminous side sills. As I don’t need this area in my design to stabilize the frame as in the original, I had a little more creative freedom here.

There are also differences to the original in terms of the amount of fuel required: While the GT40 was equipped with the largest possible fuel tanks for 24-hour races, I only need a capacity that is sufficient for about one hour of racing.

Of course, at the beginning I thought long and hard about using special safety tanks, so-called fuel cells, such as those offered by ATL. However, the search for suitable, long and flat models proved to be extremely difficult. Most of the prefabricated tanks were either too high or too wide to fit into the sills. Although it is possible to have such tanks custom-made, the price per piece is at least 2,000 euros – often even higher.

Another aspect that spoke against the immediate use of fuel cells was their limited service life: these tanks are usually only approved for five years, as the internal rubber cell has to be replaced regularly. For me, this meant that the approval might have expired before my car was ready for use.

I therefore decided on a compromise: I constructed tanks from 1 mm thick stainless steel sheet. These are fitted with baffle plates to stabilize the fuel when cornering. I also integrated maintenance hatches so that I could fill the tanks with tank foam after welding.

To further increase protection, each tank is attached to a circumferential, welded stainless steel band. This bracket is bolted to the most solid part of the side boxes, the top, with four M8 bolts each. I deliberately left as much distance as possible to the outside of the sills to provide additional clearance and protection.

I also braced the inside of the aluminum cladding of the sills between the solid, curved steel beams with 10 mm thick aluminum honeycomb sandwich panels. These panels are glued flat and supported with a 45° angle piece that reinforces the transition from the floor panel to the side wall. This construction serves purely as a crash structure and is designed to absorb energy in the event of an impact.

Of course, there is still a residual risk – that’s the price you pay when you recreate a racing car from the 1960s. Back then, the acceptance of risk was much higher than it is today, and as we all know, enough things have gone wrong

Construction of the fuel tanks

For the fuel tanks, I deliberately opted for 1 mm thick stainless steel sheet, as I was advised against using aluminum due to modern types of fuel. Aluminum tends to corrode in combination with today’s fuels, which I wanted to avoid at all costs. The tanks each measure 1155 x 220 mm with a height of 156 mm.

Inside the tanks there are three baffle plates that do not extend to the top and are each provided with five 30 mm holes at the bottom of the tank. This construction divides the tank into four chambers, which calm the fuel during rapid changes of direction. In order to be able to fill the tanks with tank foam, I attached three unscrewable lids to the top. These are large enough so that you can easily reach into the chambers by hand.

The tanks are attached using two welded stainless steel straps per tank, which are additionally stabilized by brackets. Four M8 rivet nuts per tank enable secure yet detachable fastening.

To connect the two tanks, I used two Dash 16 lines that run on the engine compartment side of the firewall. In the original, an 80 mm pipe was used for this, which ran under the backrest in the passenger compartment – an unacceptable safety risk for me. The division into two smaller pipes was necessary for reasons of space, but provides significantly more safety.

Both tanks have their own fuel caps, which are mounted directly on the tanks. I don’t need a quick refueling device, so the left and right tanks are refueled separately. The left tank contains the sensor for the fuel gauge, while the right tank houses the internal fuel pump.

After welding and before filling with safety foam, I filled the tanks with 0.6 bar pressure and carefully checked for leaks with leak detection spray. Special care is required here: 0.6 bar may seem low at first glance, but the pressure acts evenly on the entire inside of the tanks and generates considerable forces. In fact, I noticed a slight “bulge” during this step.

To ensure that the pressure does not rise too high, I have fitted an automatic pressure valve from the heating industry on a special cover for the access holes. This valve blows off precisely at 0.6 bar and thus provides additional safety during the test.

Pump system and lines

The subject of fuel pump systems alone could fill entire books – or at least detailed discussions such as those in the GT40s.com forum. Corresponding articles there illuminate all conceivable possibilities and aspects in detail. If you would like to take a closer look, you can find the articles here.

I would like to limit myself to my personal approach in this section. As with the cooling system, I wanted the design to be as simple as possible, but I can always change this later if I feel it is necessary.
That’s why I decided to go for a single fuel pump for the time being.

My engine is supplied by a classic Holley carburetor – for reasons of originality, appearance, cost and not least because of the characteristic sound. After the running-in phase and initial test drives, I could switch to a fuel injection system such as the Holley Sniper system, for example, but programming a fuel injection system seemed too complex for me to begin with.

When designing a new racing car, you should always make sure to keep the setup as simple as possible at the beginning. Even in a simple system, there are still plenty of potential sources of error. Individual areas can easily be optimized later as soon as the vehicle is running reliably

The decision to use a carburetor has a decisive advantage: I can operate the tanks without pressure. This simplifies both the ventilation and the elimination of a return circuit. The pump I use is the Phantom 200 Stealth Fuel System from Aeromotivesupplemented by the appropriate dash adapter, filter, pressure regulator and other accessories. You can find the connection diagram I used in the picture gallery below.

The lines used consist of high-quality, steel braided hoses. These not only offer high pressure resistance, but are also extremely heat-resistant – a standard that should be a matter of course for racing vehicles.

With this setup, I will try to get the car running reliably. As already mentioned: changes and optimizations are always possible. After all, it will only become clear where fine-tuning is needed when the car is in operation. We’ll see…