Rajan Wilcox
Adding a fuel return line is an essential part of an electronic fuel injection installation. A fuel return line is an integral part of the FPR system, which maintains fuel pressure by sending excess fuel back into the fuel return line. This prevents negative pressure from building up in the fuel tank. The size of the return line is important, as a line that is too small may not be able to handle the pressure and blow gas back into the tank. The location of the return line in the tank is also important, as it should be located away from the pickup to eliminate aeration.
Characteristics and Values of Adding a Fuel Return Line
| Characteristics | Values |
|---|---|
| Size of the return line | At least 5/16" |
| Location of the return line | Above or below the fuel level; away from the pickup to eliminate aeration |
| Type of return line | Braided stainless hose, steel or copper line, soft return line, hard return line |
| Purpose of the return line | To provide pressure to the injectors without changing the pressure in the fuel tank, to support more horsepower |
| Installation | Plumb in a fuel return line, ensure the regulator is installed |
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What You'll Learn
The return line should be the same size as the fuel line
When installing a fuel return line, it is generally recommended that the return line is the same size as the fuel line. This is especially true for carbed applications, as any restriction in the return line can lead to an increase in fuel pressure.
For example, if you have a 1/2" feed line, a 3/8" return line would be appropriate, as recommended by Aeromotive. This is based on the pump flow and ensures that the return line is not too restricted. It is important to note that the return line should be at least 5/16" to avoid any potential issues.
However, there are some instances where individuals have chosen to use a larger return line than the feed line. This is usually done to future-proof the setup and ensure that there is no restriction in the return line. Additionally, a larger return line can accommodate higher flow rates and prevent issues with fuel pressure.
It is also important to consider the placement of the return line in the fuel tank. Some individuals recommend returning the fuel below the existing fuel level to prevent aeration and the formation of bubbles. This can be achieved by having a hose inside the tank that goes below the lowest level of the fuel. However, others have reported no issues with returning the fuel in the top of the fuel cell, especially in larger tanks.
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Return lines can be made from steel, copper, or braided stainless hose
Return lines can be made from a variety of materials, including steel, copper, or braided stainless hose. Each material has its own advantages and considerations when used in a fuel return line.
Steel is a common choice for fuel return lines, as it is durable and holds up well against the fuel. It is often chosen for its strength and ability to withstand the pressure of the fuel system. Stainless steel, in particular, is known for its corrosion resistance and is a standard material for fuel lines in many vehicles.
Copper is another option for fuel return lines. Copper is known for its malleability and thermal conductivity, making it easy to work with and an excellent choice for heat transfer. However, copper may not be as resistant to fuel degradation as other materials, and it is essential to ensure that the copper line is compatible with the fuel type.
Braided stainless hose is also used for fuel return lines. This type of hose is typically made with a stainless steel outer braid that provides impact and abrasion resistance. It also has an inner liner, usually made of PTFE, that is designed to handle fuel and prevent leakage. Braided hoses offer flexibility and are ideal for street and racing applications where compatibility with various fuel types is necessary. However, it is essential to ensure that the braided hose is rated for fuel and can handle the pressure and temperature requirements of the fuel system.
When deciding between steel, copper, or braided stainless hose for a fuel return line, it is important to consider the specific application, fuel type, pressure requirements, and ease of installation. Each material has its own advantages, and it is crucial to select a fuel line that meets the requirements of the vehicle's fuel system to ensure safe and proper functioning.
In addition to the material selection, it is worth noting that the size and routing of the return line are also important considerations. As mentioned in the previous paragraphs, ensuring adequate line size, such as a minimum of 5/16", is crucial to maintain proper fuel flow and pressure. Additionally, the return line should be routed back to the tank, with the return bung located away from the pickup to eliminate aeration and potential fuel foaming issues. These factors, along with the choice of line material, contribute to the overall performance and reliability of the fuel system.
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Return lines can be placed at the top or bottom of the tank
However, others argue that the return line should go to the bottom of the tank to prevent aeration. They believe that if the return line is at the top of the tank, it will cause aeration, and the pump will suck in bubbles. They suggest that the return line should be as far away from the pickup as possible to eliminate aeration. Furthermore, some people mention that if the return line is at the bottom of the tank, it should have a tube to ensure that the fuel is dumped below the fuel level. This helps to prevent aeration and potential issues with the pump.
The decision on where to place the return line may also depend on the size of the tank. For larger tanks, it may not matter as much whether the return line is at the top or bottom since larger tanks have less issue with "bubbles". They have a larger volume that acts as a plenum, smoothing out turbulence in the intake. Additionally, with larger tanks, foam can be used to help prevent aeration.
It's important to note that the specific fuel system being used may also influence the decision on return line placement. Some systems may require the return line to be below the fuel level, while others may not have any issues with the return line dumping into the top of the tank. It's always a good idea to consult with experts or mechanics who are familiar with the specific fuel system in question to make an informed decision.
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A return line is an integral part of the FPR system
The return line facilitates the return of unused fuel from the engine back to the fuel tank. This is in contrast to older cars, which often lacked a return line and instead relied on a simple float valve in the carburetor to release fuel as needed. The issue with this setup is that engines can get hot, causing gasoline to turn into gas and leading to vapor lock in the fuel system.
In a system with a return line, the fuel pump continuously pumps gas through the fuel system at a much higher rate than is required. This keeps the gasoline in the fuel lines cool and prevents vapor lock. The return line also provides nearly constant pressure to the injectors, regardless of their actual demand.
When choosing an FPR, it is important to consider the type of fuel being used. For example, race cars using race fuel or alcohol will require a higher-capacity FPR, such as the FPR1200, FPR2000, or FPR3000 series. It is recommended to consult a qualified technician for proper installation and tuning of the FPR system.
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Return lines are not unique to Corvettes
The return line also keeps the fuel in the rails cooler since it is always flushing the hot fuel back to the cool fuel tank. It is nearly impossible to vapor lock a return fuel system when the car is off since any fuel that boils in the lines is blown out back to the tank when the car is restarted. On a returnless system, if enough fuel boils in the lines on a heat-soaked stop, it can be difficult to get the car to restart until it cools off.
The installation of a return line can vary depending on the car model and the type of fuel pump. For example, when installing a return line for a Holley blue pump, one user ran a fuel line and return line to the regulator, which was located at the front of the car near where the stock fuel pump would be. The return line was the same size as the fuel line. Another user installed a return line on their Fairlane with a Holley blue pump, using a 1/2" feed line and a 3/8" return line. They noted that the minimum size for the return line should be 5/16".
The location of the return line inside the fuel tank can also vary. Some people return the fuel above the fuel level, while others return it below the existing fuel level to prevent aeration and foaming. It is generally recommended to have a hose that goes below the lowest level of the fuel. The return line should also be located away from the pickup to eliminate aeration.
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Frequently asked questions
The fuel system is closed, so without a return line, there would be negative pressure on the fuel tank as fuel is pumped out. With a return line, the fuel pump can provide pressure to the injectors without changing the pressure in the fuel tank.
The return line should be at least 5/16" to avoid having to do the job twice.
The return line can be placed at the top or bottom of the fuel tank. However, it is recommended that the return line is placed at the bottom of the tank to avoid aeration.
Steel, copper, stainless steel, and rubber-covered braided hose are all options for the return line. However, it is not recommended to submerge a braided-covered rubber hose in fuel.
