hen a car accelerates or corners fast, inertia causes the fuel in the tank to ‘slop’ about. If the fuel level is low, this movement of fuel can cause the outlet pipe from the tank to be temporarily exposed allowing air to pass through the pipework. Obviously this is not good – especially on track – as any break in the supply of fuel will cause a loss of power, which could mean the difference between winning and losing a race.
Cars running carburettors can usually cope with a slight disruption in fuel supply, as most designs will have a float chamber with enough fuel available to overcome the surge. In fuel injection applications however, even the slightest exposure of the tank outlet will result in air entering the system. At best,
this will cause nothing more than a momentary engine splutter, however, repeated fuel starvation can begin to damage pumps and engine components.
All modern fuel injected cars will come with systems to stop fuel starvation, which will include baffling or foam filling of tanks and a swirl pot of some description. The swirl pot is a small reservoir of fuel held in a separate smaller section of the main tank, or as a completely independent unit, that will ensure fuel is available at the injectors whatever cornering, braking or accelerating forces are affecting the car, even at low-fill volumes.
Modified and race cars often have the standard tank removed and run low fuel levels, so it is important to make sure a swirl pot is incorporated in the design of the new fuel delivery system. This is usually in the form of an alloy tank located independently from the main tank, which will hold between one and two-litres of fuel. A low pressure ‘lift pump’ such as the Facet Red Top type, will supply fuel to the swirl pot via its inlet (usually 8mm) located somewhere near the middle to top of the pot. Fuel leaves via a bigger outlet (12mm) drawn by a high-pressure pump, which then feeds the fuel rail via a filter. It’s important to note too that the HP pump should be located below the level of the swirl pot.
Most swirl pots have two other connections. One near the top is an overflow return to the fuel rail and a smaller one at the very top is a vent which returns vapours to the main tank.
The best location for a swirl pot is in the boot area. This is both to get it near the fuel tank so the low-pressure pump doesn’t have to work too hard and just in case the pot or its connections fail. It’s far better to have a fuel leak away from the driver and at the opposite end of the car to the hot engine and exhaust system.