A fuel surge tank (a.k.a. swirl pot, reservoir) is an integral part of a modern electronic fuel injected race car. Many modern high performance cars have them as well, especially once with turbocharged engines. Its purpose is to ensure the engine has a constant and uninterrupted supply of fuel even while the car is in a corner which is pushing all the gas in your main tank to one side. When that happens, the main tank pump can’t pick any fuel up and starts pumping air, which is not good and in a worst-case scenario can blow your engine.
To prevent this, a fuel surge tank allows for a setup of two interconnected pumping systems joined through this secondary reservoir which ensures a constant supply of fuel to the engine. The first and relatively low pressure fuel pump takes the gas out of the main tank and pumps it into the surge tank. Once the tank is full, the gas circulates constantly back into the main tank. Concurrently, gas is pumped at high pressure from the surge tank to the engine, again with a return line back to the surge tank for a total of four connections on the surge tank (two systems, two pumps). With this setup, when the car is cornering at high g forces and the fuel in the main tank is relatively low, the engine can still be fed an uninterrupted supply from the surge tank because it was pumped full prior to the corner while the main pump was still able to pick up fuel.
With those basics of a fuel surge tank system, there are of course many opinions on what kind of setup you need, how big of a tank, what pumps are suitable, etc. In the end, everyone’s setups and goals are different, so there’s no one size fits all approach. For example, one feature many feel they need is the for the fuel to be truly “swirled” in the pot which releases any air bubbles which may have introduced themselves. This can be done by a large cylindrical tank that has the inlet placed so that it forces fuel to spin in a circle inside the tank (see picture to the right). Another option is to use an in-tank pump in the main tank with a fuel sock which soaks fuel up to pump while most of it is pushed to one side. You can also create sections in your tank and put your pump pickup at the lowest point to give it lower chance of sucking air. Or some OEM in-tank pumps like the Porsche GT2, GT3 and Turbo pump has a small built-in reservoir and uses tentacle-like venturi tubes in combination with a unique tank design to always pick up fuel from the lowest point. I’m sure there are lots of other strategies I haven’t even considered. To boot, I’ve also seen many discussions on tank size based on expected worst-case scenario fuel requirements which is almost a topic worthy of its own post, so suffice it to say, fuel surge tanks was a much more involved topic than I’d ever expected and I just had to make my own conclusions.
In the end I balanced noise (as low as possible), need for swirling (I wasn’t convinced), size (I didn’t need anything huge) and mounting location flexibility in purchasing a unit designed by 034 Motorsports which submerges the legendary Bosch 044 pump. At 1 liter capacity, many will think it’s a very small pump, but I think it’s the most cleverly engineered one that I came across. It had to be an external system, because I couldn’t do anything in-tank. On the SLC, the tank design makes an in-tank pump hard unless you’re willing to slice the tank open, design an easy maintenance access solution and re-weld – not exactly my area of expertise at this time.
You can see the surge tank with the fuel pump mounted within it on the right. Notice how the fuel pickup on the left works: even if you mount the tank horizontal, it will pick up from the lowest point, though obviously it’s best to mount the tank vertically. There are four outlets on the top, which you can see in the picture of the individual pieces below, but with three holes are the bottom, you can also have all lines except the high pressure out line attach at the bottom if it’s easier to plumb.
In my selection of this tank, the submerged Bosch 044 was a key factor for two reasons. One, the 044 is a tried and true unit that seems to be by far the most popular aftermarket high pressure pump to the point of being standard and two, while it’s a great pump, it’s noisy unless it’s submerged and I’m trying to build a car which is very streetable. It would suck to have a constant clicking noise buzzing around. I’ve assembled the pump as far as I could without a car and I don’t have the car yet, but so far I’m very happy with my choice. Below is a picture of the individual pieces that make up the pump prior to assembly. The base is on the left, the cylindrical housing in the middle and the inverted top with the Bosch 044 pump attached is upside down on the right. This all screwed together pretty easily.