Rajan Wilcox
Fuel line sizing is an important consideration when designing a fuel system. The size of the fuel line can impact the performance of the engine and the amount of fuel required. For example, a 3/8”id fuel line can support 600 HP, and a 3/4″ pipe size can be sufficient for a very old fuel manifold system. The type of fuel also plays a role in fuel line sizing, with ethanol and methanol requiring larger fuel lines than gasoline. Manufacturers of in-line fuel pumps often recommend a fuel line diameter that works best with their pumps to prevent starving the pump. When determining the size of a fuel line, it is important to consider factors such as the engine's maximum values, pressure drops, and the supply and return sides of the system.
| Characteristics | Values |
|---|---|
| Fuel restriction | 1/4″ & 3″ of Hg |
| Most common fuel restriction | 1.0 to 2″ Hg |
| Fuel line diameter | 3/8” |
| Fuel line diameter for ethanol | 30% larger than gasoline |
| Fuel line diameter for methanol | Double the size of gasoline |
| Return line fuel line diameter | One size smaller than the feed line |
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What You'll Learn
Fuel line sizing for a typical fuel system
The size of the fuel line is important to ensure that the engine receives the correct amount of fuel. For example, ethanol requires about 30% more fuel than gasoline to generate the same horsepower, so the fuel line for ethanol should be one to two sizes larger than the gasoline requirement. Similarly, methanol requires double the amount of fuel as gasoline, so the fuel line should be sized accordingly.
The supply or suction side of the system often receives the most attention because most operators equate fuel restriction with performance. However, it is important to consider the return side (restriction-pressure of the return line) as well. The return lines, which are the fuel lines after the regulator, can generally be one size smaller than the feed line.
When sizing a fuel line, it is also important to consider the length of the line. For example, if you have 10 feet of 3/8" fuel line, you may need to double that to 20 feet to account for bends in the steel pipe from the gasoline tank to the engine fuel rail.
Finally, the pump size also plays a role in fuel line sizing. A 3/8" steel line can support up to 1000 HP given a big enough pump.
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Fuel line sizing for ethanol and methanol
Fuel line sizing is a complex topic, and it's important to get it right to ensure your engine performs well and doesn't get damaged.
When it comes to ethanol and methanol, these fuels have become increasingly popular in recent years, especially with high-horsepower turbo supercharged blown EFI engines. Ethanol is cost-effective and can provide the octane and power potential needed for demanding applications. It also has a cooling effect on intake charges. However, it can be corrosive and may damage fuel system components that would otherwise be unaffected by gasoline. Methanol will require double the amount of fuel than gasoline to generate the same HP.
When designing a fuel line system for ethanol and methanol, it is recommended to go one to two sizes larger than the gasoline requirement. The return lines, which are the fuel lines after the regulator, can generally be one size smaller than the feed line.
It's also important to note that special fuel filters must be used with ethanol and methanol, and you need to ensure your fuel pump is compatible.
In general, a good number to aim for when all is clean is between 1/4″ & 3″ of Hg total fuel restriction, with about 1.0 to 2″ Hg most common in a well-designed fuel system. Additionally, when determining the size of your fuel lines, it's crucial to consider the factory's maximum values, numbers, or pressure drops that the engine can tolerate for both the supply side (suction) and the return side (restriction-pressure of the return line).
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Fuel line sizing for a gasoline tank
When determining the size of the fuel line, it is important to consider the engine's maximum values, numbers, and pressure drops that it can tolerate for both the supply side (suction) and the return side (restriction-pressure of the return line). The supply or suction side of the system tends to get the most attention because most operators equate fuel restriction with performance. However, it is important to note that while the two can be equated, it is not as most people think.
The size of the fuel line can also depend on the type of fuel being used. For example, ethanol requires about 30% more fuel than gasoline to generate the same HP, while methanol requires double the amount of fuel. When designing a fuel line system for these fuels, it is recommended to go one or two sizes larger than the gasoline requirement. The return lines, which are the fuel lines after the regulator, can generally be one size smaller than the feed line.
Additionally, the length of the fuel line can impact the size required. For example, if using 20 feet of steel pipe, the pressure drop can be calculated as 3 psi using water (gasoline flows more freely). Increasing the line size to 1/2″ may help reduce the pressure drop.
Finally, the pump head and the size of the pump also play a role in determining the size of the fuel line. A 3/8″ steel line can support 600 HP given sufficient pump head, and with a big enough pump, it could even support 1000 HP.
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Fuel line sizing for a fuel pump
The return lines, which are the fuel lines after the regulator, can typically be one size smaller than the feed line. It's worth noting that the supply or suction side of the system often receives more attention as most operators equate fuel restriction with performance. However, this is not always a straightforward correlation. The factory's maximum values, numbers, or pressure drops that the engine can tolerate for both the supply side (suction) and the return side (restriction-pressure of the return line) are important factors to consider.
When it comes to specific fuel line sizes, a 3/8" fuel line is commonly used and can support up to 600 HP with sufficient "pump head". A bigger pump can even allow a 3/8" steel line to support 1000 HP. Additionally, a well-designed fuel system should aim for a total fuel restriction between 1/4" and 3", with 1.0 to 2" Hg being the most common range.
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Fuel line sizing for a fuel manifold system
When it comes to fuel line sizing for a fuel manifold system, there are a few key considerations to keep in mind. Firstly, it's important to understand the factory's maximum values, numbers, or pressure drops that the engine can tolerate for both the supply side (suction) and the return side (restriction-pressure of the return line). This is crucial in ensuring that the fuel line is sized correctly for optimal performance.
A typical fuel system with proper sizing should have between 1/4" and 3" of Hg total fuel restriction, with 1.0 to 2" Hg being the most common in a well-designed system. The supply or suction side of the system often receives the most attention as operators equate fuel restriction with performance. However, it's important to note that while there is a correlation between the two, it may not be as direct as most think.
When selecting a fuel line diameter, it's important to consider the recommendations of in-line fuel pump manufacturers. They often suggest a size that works best with their pumps to prevent starving the pump. It's also worth noting that different fuels have varying requirements. For example, ethanol requires about 30% more fuel than gasoline to generate the same HP, while methanol requires double the amount. As a result, when designing a fuel line system for these alternative fuels, it's advisable to go one to two sizes larger than the gasoline requirement.
Additionally, the return lines, which are the fuel lines after the regulator, can typically be one size smaller than the feed line. In terms of specific sizes, a 3/8" fuel line is commonly used and can support up to 600 HP with sufficient "pump head". If a larger pump is utilised, a 3/8" steel line could even support up to 1000 HP. It's worth noting that pipe bends and length can also impact performance, so these factors should be considered when sizing the fuel line.
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Frequently asked questions
A 3/8”id fuel line can easily support 600 HP given sufficient “pump head”.
A 3/8” steel line can support 1000 HP with a big enough pump.
Methanol requires double the amount of fuel than gasoline. When designing a fuel line system for methanol, go one or two sizes larger than the gasoline requirement.
