Fuel Surge Tank
Here you get an overview of how a fuel surge tank work, which parts are included and what options are available. Fuel catch tank is sometimes (carelessly) called just catch tank, which is easily associated with oil catch tank if it doesn't have a context.
- What does a fuel catch tank do?
- Fuel catch tank selection
- Different versions
- Connecting a fuel catch tank
- Compare Fuel surge tanks
What does a fuel catch tank do?
A fuel catch tank ensures that fuel is always available at the spreader even if you make sharp turns, such as when driving on a track.
Problem: During sharp turns, the fuel in a fuel tank moves to the side, along the sides. When a fuel pump sits in the middle, it cannot access the fuel. Therefore, it sucks air and cannot supply fuel to the engine. This can cause engine damage. Since sharp turns happen all the time in racing, this is a problem.
Solution: A so-called surge tank (a small tank around 1-3 litres) is assembled together with an extra fuel pump. This surge tank is fed with fuel from the fuel tank. The additional pump then sucks from the surge tank and feed fuel to the engine. The return line from the engine goes back to the surge tank as an extra fuel refill. The surge tank also has a return line that lead excess fuel back to the fuel tank.
Summary: In this way, the fuel surge tank will always have available fuel to deliver to the engine, even when the pump in the fuel tank lack fuel access (fuel starvation)
Fuel surge tank selection
Type of surge tank
Different types of tanks are available where fuel pumps can be mounted internally or externally. A tank for external pumps is actually a simple container with connections for pumps. A tank for internal fuel pumps is often larger to accommodate the pumps. Internal fuel pump hanger and power supply must also be available for mounting the pumps.
A tank made for internal pumps can also be used with externally mounted fuel pumps. In these cases, pipes or adapters must be used to be able to collect fuel from the bottom of the fuel surge tank.
Size / Volume
The size of surge tanks varies and here it is advantageous to use a larger tank if space is available. The tanks are available from 0.5 to 4 litres. In competitions, however, it may be regulated with a maximum size of the tank. Often 1-1.5 liters approximately
Keep in mind that if your tank is 3 liters and an internal fuel pump is fitted, the total fuel volume will be less than 3 liters as the internal pump takes up space and reduces the total fuel volume. If 2 or 3 pumps are installed, the total fuel volume is further reduced.
Number of fuel pumps
The number of pumps that can be mounted in a fuel tank that is adapted for internal fuel pumps is usually 1-3. A tank that allows the installation of 3 internal pumps can also be used together with 2 or 1 pump as well, but then the extra holes must be plugged.
Fuel surge tank material
Catch tanks are mainly available in two material variants.
- Welded tank that is round or square. These are usually made of aluminium
- Milled aluminum which is often cylindrical in shape.
There are a few different types of fuel surge tanks.
Separate surge tank mounted outside the fuel tank
A separate catch tank that constantly have with a small overpressure is the most flexible catch tank solution as the number of pumps, size and connections can be chosen as you want.
Built-in surge tank in fuel cell lid
This solution is incredibly flexible. A built-in surge tank in the fuel cell / fuel tank that have a slight over pressure, just like a real surge tank does. Here, however, you are limited to the connections and size that are available, but this is usually not a problem as there are many different types of pumps to choose from. This variant is costly but very effective in terms of function and location.
Baffles in fuel cell
This is also a flexible solution where baffles inside the fuel cell act as a catch tank. This cannot be compared to a real catch tank that constantly have overpressure. But with this solution, you can in a simple and very affordable way install a fuel tank with a catch tank function, keeping the fuel around the fuel pump, exactly the same idea as with a catch tank.
Tank foam in fuel tank / fuel cell
This type is the least reliable as some believe that the tank foam wears out / dissolves and sticks / blocks fuel pumps and filters. However, this solution is very easy to assemble. The foam just needs to be pushed down into the tank through the hole where the fuel pump holder sits. Make sure the fuel level gauge is not blocked.
Connections on a fuel catch tank are in the vast majority of cases located on top of the tank. If external pumps are used and fuel is to be collected from the bottom of the fuel surge tank, two pipes / adapters need to be mounted in the tank that reach down to the bottom.
The number of connections depends on the type of tank used.
The following connections are available on a fuel surge tank:
- Inlet from fuel tank
This is usually just one connection as the feed pump from the fuel tank works almost completely without back pressure and flows very well compared to main pumps that work with back pressure created by the fuel pressure regulator.
- Return line to fuel tank
This return line returns excess fuel from the surge tank to the fuel tank.
- Outlet to engine
This outlet can be one, two or three connections depending on how many pumps are supported. If the surge tank is prepared for three pumps but only one is used, two holes must be plugged.
- Return line from engine
The return line from the engine goes back to the surge tank. In this way, the surge tank have fuel flowing in from two places and is always full.
- Electrical connector
If the surge tank is prepared for internal fuel pumps, there is usually a connector / connections / terminals for powering the fuel pumps. If the tank support more pumps, there are usually also more connections.
The fuel surge tank can be mounted where there is space or where the installation is best suited. It is mostly fuel pumps that must be taken into account when it comes to location of the surge tank.
The pre fuel pump that sits in the standard fuel tank or fuel cell supplies a catch tank with fuel and work without back pressure, or very little back pressure. This ensures that even the original fuel pump would be able to deliver fuel to a system with a highly tuned engine. The downside is that the original fuel pump may have run many thousands of miles and is old. Therefore, this pump is perhaps not so reliable. Pre-filters and other parts can also be hard to come by. Therefore, the pump is replaced with a new model to ensure proper function..
Feed fuel pump from surge tank to the engine. These pumps supply the engine with the fuel required for the desired engine power output. This type of pump can be mounted inside the surge tank (internal pump) or outside the tank (external pump). If you mount the feed pump as an external pump, these must not sit above the catch tank fuel level. These pumps must therefore not drag the fuel from the surge tank, but must be fed with fuel. Even if the connections are located at the top of the surge tank, the feed pumps must be leveled at the bottom of the catch tank.
The pumps can suck / drag fuel but are not designed to work like that.
Large pumps that run all the time heat the fuel. A fuel cooler can be fitted but keeping the fuel pump down with the right sized pumps is a good first solution. For example, the pumps can be PWM controlled. Or one pump can start only at a time as fuel is needed.
By using internal fuel pumps, the noise from the fuel pumps is drastically reduced. However, heat from the pumps will be transferred to the fuel, which also increases the fuel temperature. External fuel pumps make more noise but do not heat the fuel. This is marginal but can be a factor if engine power is to be optimized.
Feed pump to fuel catch tank
The feed pump from fuel tank to catch tank work without back pressure. Therefore, this pump flow more than the corresponding one that works with back pressure. This mean that even a less powerful fuel pump can be used to feed the fuel surge tank even if the engine is heavily tuned.
Feed pump = Low / No back pressure = Max flow
The amount of fuel with internal pumps
The amount of fuel a fuel catch tank can hold is often indicated as without fuel pumps fitted. If internal fuel pumps are installed, you should consider deducting this fuel quantity.
Connecting a fuel catch tank
Fuel system with fuel catch tank - internal fuel pump
Option 1 - BTR after fuel rail
Fuel pump in fuel tank -> Fuel pump in fuel catch tank -> Fuel filter -> Fuel rail / Carburetor -> Fuel pressure regulator -> Return to fuel catch tank -> Return to fuel tank.
Option 2 - BTR before fuel rail
Fuel pump in fuel tank -> Fuel pump in fuel catch tank -> Fuel pressure regulator (overflow in return to fuel catch tank -> return to fuel tank) -> Fuel rail / Carburetor.
Fuel system with fuel catch tank - external fuel pump
Option 1 - BTR after fuel rail
Fuel pump in fuel tank -> Fuel catch tank -> External fuel pump -> Fuel filter -> Fuel rail / Carburetor -> Fuel pressure regulator -> Return to fuel catch tank -> Return to fuel tank
Option 2 - BTR before fuel rail
Fuel pump in fuel tank -> Fuel catch tank -> External fuel pump -> Fuel filter -> Fuel pressure regulator (overflow in return to fuel catch tank -> return to fuel tank) -> Fuel rail / Carburetor.
- Fuel system: Components and assembly
- Fuel system: Common problems
- Choose the correct fuel injector
- Check valve - Information
- Compare Fuel injectors
- Different Type of Fuels [Gasoline or Ethanol?]
- Different types of fuel systems
- Fuel catch tank / Fuel surge tank
- Fuel cell
- Fuel filler
- Fuel filter
- Fuel pressure regulator
- Fuel pump
- Fuel Pump Hanger - Information
- Fuel rail
- Injector flow - Horsepower rating
- Injector size
- Tank ventilation