Rajan Wilcox
When it comes to the fuel system in a car, there are several factors to consider, including the type of hose, its placement, and the regulations that need to be followed. The fuel line's routing is crucial to prevent issues such as vapor lock caused by baking the fuel, and to keep it away from the drivetrain and potential scrub line interference. The hose material is also important, with options like rubber, Teflon/PTFE, or stainless steel-braided hoses, each having advantages and disadvantages in terms of cost, flexibility, and resistance to fuel vapour escape. Additionally, rules from organisations like NHRA, IHRA, and SCCA dictate specific requirements for fuel lines, such as their location and the need for bulkheads or specific materials like braided steel. Understanding these factors is essential for anyone looking to modify or improve their car's fuel system.
| Characteristics | Values |
|---|---|
| Fuel line routing | Over the top of the passenger-side inner fender and down along the curbside of the frame rail and frame connector |
| Fuel line material | Vinyl/plastic, rubber, or Teflon/PTFE-lined with a stainless-steel over-braid |
| Fuel line protection | Bulkhead, encased in a steel tube, or braided steel |
| Fuel line location | Away from the drivetrain, bellhousing, and scrub line |
| Fuel line mounting | As high as possible to avoid potential scrub line interference |
| Fuel filter mounting | Accessible for servicing, with spacers for easy access to either end |
| Fuel pump mounting | Near the engine |
| Fuel return line | May require a regulator to allow the fuel system to pressurize |
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What You'll Learn
Fuel lines inside the car
Fuel lines inside a car are an essential component of the fuel system, and their routing and placement are crucial for safety and performance. While regulations and preferences may vary, some general principles and industry standards guide the installation of fuel lines inside a car.
Firstly, it is generally recommended to keep fuel lines away from the driver's compartment or passenger area. Regulations from organisations like NHRA, IHRA, and SCCA mandate specific requirements for fuel lines in the driver's compartment. For example, fuel and oil lines passing through this area might need to be bulkheaded or encased in a steel tube to enhance safety.
The routing of fuel lines is a critical aspect of their design. In some cases, fuel lines are routed over the top of the passenger-side inner fender and then down along the curbside of the frame rail. This setup helps maintain a safe distance from the drivetrain, particularly the bellhousing. Additionally, keeping the fuel lines away from the engine heat is essential to prevent issues like boiling the fuel, which can lead to vapor lock.
The flexibility and material of the fuel lines are also important considerations. Rigid vinyl/plastic lines may have a fixed loop that doesn't provide tension release. Flexible hoses, such as push-on hoses, are cost-effective but not recommended for inside the car due to their tendency to allow vapour and fumes to escape, creating an unpleasant environment in the cockpit. Teflon/PTFE-lined hoses are a better choice for inside the car as they prevent the escape of fuel vapour and eliminate stale fuel smells.
When designing a fuel system, it is advisable to first determine the placement of components like the fuel pump and filter. Fabricating spacers and using L-shaped bulkhead plates can help mount the feed and return lines neatly and securely. The type of fittings and hoses used will depend on the specific requirements of the car, with most production cars utilising push-on hoses.
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Fuel line routing
Additionally, heat from the engine and exhaust system can bake the fuel, leading to vapor lock. To mitigate this, the fuel line should be kept away from the headers, and the forward line(s) can be routed over the top of the inner fender. A bulkhead plate can be fabricated and mounted to the inner fender to facilitate this setup. The fuel filter should also be easily accessible and mounted in a spot where it can be serviced. It is also important to consider the movement of the engine and allow for some give in the fuel line.
Furthermore, the fuel line should be secured and protected from heat. Hose clips or swaged-on methods can be used, with options for low or high pressure. The use of rubber hoses inside the car is not recommended due to the escape of vapour and fumes, while Teflon/PTFE-lined hoses can be used both inside and outside the car as they prevent the escape of fuel vapour. Stainless steel over-braid can provide additional protection against cuts and abrasion.
When routing the fuel line, it is also important to keep it away from any potential scrub line interference. This refers to any part of the car that would rub or scrub if a tire goes flat or a wheel departs. In the event of an accident, clearly marking the fuel lines can help emergency services identify them and prevent further damage.
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Fuel line materials
Fuel lines are essential components in a car's fuel system, facilitating the efficient transfer of fuel from the tank to the engine. The choice of fuel line material is critical to ensuring the safe and reliable delivery of fuel. Several factors, such as durability, flexibility, compatibility, and heat resistance, come into play when selecting the appropriate material.
Metal fuel lines, made from stainless steel, aluminum, or coated steel, are renowned for their durability and compatibility with various fuel types. They offer superior resistance to wear and tear, cracking, and deterioration. Metal lines are also less susceptible to fuel vapor issues compared to rubber or braided lines. However, metal lines can be challenging to fabricate and install due to their rigidity, especially when larger diameters are required.
Rubber fuel lines, on the other hand, offer exceptional flexibility, making them ideal for installation in tight or hard-to-reach spaces. They are easy to install, typically using barbed fittings and fuel line hose clamps. However, rubber lines have a shorter lifespan as they are prone to degradation when exposed to fuel. They may also be incompatible with certain fuels or chemicals.
Braided fuel lines, which are rubber hoses with a braided stainless or nylon exterior, offer enhanced durability over plain rubber lines. They utilize AN hose ends for connections, providing a superior seal. However, braided lines are still susceptible to degradation from fuel vapors and may develop leaks if the braid sustains damage.
PTFE-lined fuel lines, featuring a PTFE liner and a braided stainless or nylon exterior, represent the best option among soft hoses. The PTFE liner actively blocks fuel vapors and significantly slows down the degradation process. Additionally, PTFE-lined hoses offer excellent resistance to heat and chemicals. However, they require special fittings and are less flexible than standard braided or rubber hoses.
Nylon tubing is another budget-friendly option for fuel line repairs, offering a more durable alternative to plain rubber fuel hoses. Steel pipes are commonly used in vehicles with fuel tanks at the rear, providing a cheap and robust solution. However, steel pipes are prone to corrosion, which can lead to fuel leaks over time.
In summary, the choice of fuel line material depends on the specific requirements of the vehicle and its fuel system. Metal lines offer superior durability and compatibility, while rubber and braided lines provide flexibility and ease of installation. PTFE-lined hoses excel in vapor and heat resistance, making them the best soft hose option. Ultimately, the selected material should comply with racing regulations and ensure the safe and efficient delivery of fuel.
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Fuel system plumbing
Planning
It is recommended to start by drawing a simple diagram of where you intend to mount the various components. This allows you to visualise the setup and anticipate any issues before beginning the installation. It is also important to determine the criteria for choosing the right parts, such as the type of fittings required. Most production cars use push-on hoses with an 8mm bore.
Hose Selection
The hose is a vital component that joins all the fuel system parts together. There are several options to choose from:
- Push-on Hose: This is a cost-effective solution for renewing fuel lines, although it is not recommended for inside the car. While it won't leak, it allows vapour and fumes to escape, making the cockpit unpleasant. It is flexible and requires supporting clamps for long lengths. The high ethanol content in pump fuel can also shorten the lifespan of cheaper hoses.
- Teflon/PTFE Lined Hose: This type of hose can be used inside or outside the car as it prevents the escape of fuel vapour. It features a stainless-steel over-braid and comes in various sizes. The fittings create a strong connection and have different colour options. This hose is ideal for long lengths due to its low internal friction and small outside diameter, making it suitable for tight installations.
Routing
When routing the fuel lines, it is important to keep them away from the engine's heat and the drivetrain. One common method is to route the lines over the top of the passenger-side inner fender and then down along the curbside of the frame rail and frame connector. This setup also helps to avoid any potential scrub line interference. The lines should be mounted as high as possible to further minimise interference.
Bulkheads and Protection
Fuel lines in the passenger compartment are often restricted or require specific protection. A bulkhead or divider between the driver and the fuel cell is usually necessary. Steel lines are preferred over rubber hoses in the driver's compartment for safety reasons. Braided steel lines or encasing the lines in a steel tube are also options to consider.
Fuel System Components
Other components to consider include the fuel pump and filter. The filter should be mounted in a readily accessible location for servicing. A return line and a bypass valve are also necessary parts of the fuel system. Additionally, if the car has a replacement tank without an in-tank pump, a regulator may be required in the return line to allow the system to pressurise.
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Fuel line safety
There are several factors to consider when it comes to fuel line safety. Firstly, the type of material used for the fuel line is critical. In the past, rubber hoses and plastic filters were commonly used, but today's fuels have a higher ethanol content, which can break down rubber over time, leading to leaks. As such, it is recommended to use steel lines, particularly on the pressure side of the fuel system, as they are more durable and less prone to cracking or splitting.
Secondly, the routing of the fuel line is important. The line should be kept away from the engine and exhaust system to prevent baking or boiling the fuel, which can result in vapor lock. One common method is to route the lines over the top of the passenger-side inner fender and then down along the curbside of the frame rail, keeping it away from the drivetrain. Additionally, the fuel line should be mounted as high as possible to avoid any potential scrub line interference.
Another safety consideration is the inclusion of a bulkhead or firewall between the driver's compartment and the fuel cell. This provides protection for the driver in the event of a fuel leak or fire. Some racing organizations, such as NHRA and IHRA, mandate that the fuel cell be sealed off from the passenger compartment. Braided steel lines are also often used to provide additional safety.
Furthermore, it is important to regularly inspect and maintain fuel lines. Owners should have their lines inspected and repaired as needed to ensure proper and safe operation. This includes checking for any signs of wear, cracks, or leaks, and replacing old or damaged lines.
Finally, some vehicles are equipped with a crossover fuel line safety valve, which functions as a "fuse" in the fuel line. This valve automatically shuts off the fuel flow if the line between the main and auxiliary tanks is damaged or obstructed, reducing the risk of fire and minimizing fuel loss.
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Frequently asked questions
A loop is not a necessity for a car fuel line but it is recommended to keep the fuel line away from the drivetrain of the car and to prevent vapor lock.
Vapor lock is when the fuel boils due to the line's location, which tends to bake the fuel.
It is important to keep the fuel line away from the heat of the engine and the exhaust system. The filter should be mounted in a spot where it is easily accessible and the fuel line should be protected from any potential scrub line interference.
The type of hose used for a fuel line depends on the application. Plain rubber hose can be used for carburettors and stainless steel braided hose can be used for fuel injection. Teflon/PTFE-lined hose can be used inside and outside the car as it prevents the escape of fuel vapour.
Fuel lines in the passenger compartment are either completely banned or need specific protection. They may be permitted with strict control over location and material.
