Make your own surge tank
Subarus are renowned for fuel surge when the fuel in the tank gets around 1/4, what happens is the g-forces when cornering pushes the fuel away from the fuel feed to the fuel pump, so the pump ends up pumping air instead of fuel. Leaning the engine and causing a rather big loss of power, almost enough for you to head butt the stearing wheel.
To fix this problem we install a surge tank. A surge tank is a resivoir which holds extra fuel, for the high pressure pump to pick up if flow from the main tank is lost.
Usually the tank is mounted in the engine compartment. Fuel is piped to it by either a stock engine driven mechanical pump or a low pressure electric pump. Often the stock electric pump can be used. A high pressure EFI pump will be mounted below the surge tank. The fuel gravity feeds into this pump and goes to the fuel rail. Fuel not used by the engine is returned from the rail, through the fuel pressure regulator, to the top of the surge tank. From here, if the surge tank is full, fuel is returned back to the main fuel tank.
 |
 |
Most tanks will have three fittings on the top, one for feed from the low pressure pump, one for fuel returned through the fuel pressure regulator and one for the return back to the main fuel tank. Usually only one fitting is used on the bottom of the tank for feeding the high pressure pump.
Tanks are usually about 1/2 to 1 liter in capacity, made from either steel or aluminum. The tubing is usually 2.5 or 3 inch diameter and .050 to .075 wall thickness. A long tank allows any trapped air to rise to the top so it does not enter the high pressure pump. Threaded bosses are welded to the top and bottom caps or sides as in the example above. Note the surge tank doesn't have to be round, it can be almost any shape you like within reason.
