Rajan Wilcox
Plumbing a fuel system can be a complex task, especially when dealing with mechanical pumps and regulators. The process involves careful planning and consideration of various components, including fuel tanks, pumps, filters, regulators, and hoses. One key aspect is determining the placement of the fuel pump, which can vary depending on the vehicle's design and specifications. The type of fuel and its compatibility with the fuel hose is another important factor, as certain fuels like Ethanol can degrade cheaper rubber hoses. Proper fittings, such as AN (Army/Navy) fittings, are essential to ensure secure connections and prevent leaks. Additionally, the size and routing of hoses play a crucial role in achieving optimal performance, with sharp turns requiring angled fittings. When working with mechanical pumps and regulators, it's important to follow manufacturer guidelines and seek expert advice to ensure a safe and effective fuel system installation.
How to plumb fuel lines with a mechanical pump and regulator
| Characteristics | Values |
|---|---|
| Fuel hose | R9 specification hose is recommended to avoid fuel leaks and fires |
| Fuel tank | The heart of the fuel system |
| Fuel pump placement | If using an electric unit, placement is key; mount it under the car directly in front of the gas tank |
| Fuel pump type | Mechanical pumps are preferred over electric pumps |
| Fuel line size | -10 line from the tank to the pump, -10 line to the regulator, -6 or -8 to the carb, -10 return line from the regulator to the tank |
| Fuel pressure | If the pump provides higher pressure than required, an adjustable regulator can be used for fine-tuning |
| Fuel regulator | A regulator may need to be added to the return line to allow the fuel system to pressurize |
| Fuel sampling kit | Required for cars used in rallying; can be push-on hose types or threaded male/male or male/female |
| Fuel hose security | The fuel hose should be secured to prevent movement and protected from heat |
| Fuel hose bends | For sharp turns, use angled fittings (e.g., 45- or 90-degree) instead of bending the hose; a 3-inch radius is the maximum bend for a rubber hose |
| Plumbing components | Earl's Performance Plumbing offers fittings and hoses to suit different systems' needs |
| Plumbing planning | Proper planning is key to reducing frustration; aftermarket plumbing involves AN fittings, which correlate with specific outside diameters of metal tubing |
| Plumbing connections | Carburetors are generally push-on connections, but threaded connectors are offered for specific brands |
| Plumbing maintenance | Replacing stock plumbing with aftermarket parts can be overwhelming; expect obstacles and proper planning |
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What You'll Learn
The importance of a surge tank
Fuel lines can be plumbed using a mechanical pump and regulator, and this can be done in a variety of ways depending on the specific setup and requirements of the engine. The process typically involves running fuel lines from the tank to the pump, regulator, carburettor or injectors, and back to the tank, with various fittings, connectors, and clamps used to secure the lines in place.
Now, let's discuss the importance of a surge tank in this context:
A surge tank is a crucial component in a fuel system, especially for high-performance race cars or vehicles with carburettors that have been converted to fuel injection. Its primary function is to maintain a consistent supply of fuel to the engine, preventing fuel starvation and ensuring optimal engine performance. Here are the key reasons why a surge tank is important:
- Consistent Fuel Delivery: During high-performance driving conditions, the fuel in the main tank can slosh around, leading to inconsistent fuel delivery to the engine. A surge tank acts as a secondary reservoir, providing a constant level of fuel to the engine even during rapid acceleration or sharp turns. This helps to prevent fuel starvation and ensures the engine always has enough fuel to perform optimally.
- Buffer and Protection: A surge tank serves as a buffer between the main tank and the engine. In the event of a sudden fuel supply failure, the surge tank provides a reserve to minimise the risk of engine damage, especially at high power outputs and RPMs. This added protection can be crucial for maintaining engine health and performance.
- Improved Fuel Delivery: By using a surge tank, the fuel delivery system becomes more efficient. The surge tank ensures that high-pressure fuel pumps always have enough fuel available, preventing issues with inconsistent fuel flow that can occur during high-performance driving. This results in improved engine performance and responsiveness.
- Adaptability: Surge tanks are versatile and can be used with various fuel pumps and systems. They are designed to work with some of the most common fuel pumps on the market, making them accessible and adaptable to different vehicle setups. This versatility allows enthusiasts and mechanics to implement surge tanks in a wide range of applications.
In summary, a surge tank is important as it ensures a consistent and reliable fuel supply to the engine, protecting the engine from damage and optimising performance, especially in high-performance driving conditions. By acting as a secondary reservoir and buffer, the surge tank ensures that the engine always has the fuel it needs, contributing to a more efficient and responsive fuel delivery system.
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Fuel line sizing
The most common sizes for fuel lines in mechanical pump systems are -6, -8, and -10. These sizes correspond to specific diameters, with -6 being approximately 9/16" (0.5625 inches), -8 being 3/4" (0.75 inches), and -10 being close to 5/8" (0.625 inches). It's important to note that these sizes are standard, but the actual dimensions may vary slightly between manufacturers.
When selecting the appropriate fuel line size, it's crucial to consider the type of fuel used. For example, when using alcohol or E85 fuel, the flow requirements increase. With alcohol, the flow needs to be doubled, while with E85, a 30% increase in flow is necessary. This means that a larger fuel line or a more powerful pump may be required to ensure sufficient fuel delivery.
In addition to fuel type, the horsepower of the engine plays a role in fuel line sizing. Higher horsepower demands more fuel, and as a result, a larger fuel line may be needed to accommodate the increased flow. However, it's important to remember that a larger fuel line alone may not be sufficient. The pumping power, pump size, and pump voltage also contribute to ensuring an adequate fuel supply.
Another factor to consider is the viscosity and surface tension of the fuel. Gasoline, for instance, has lower viscosity and surface tension compared to water, which is why it flows more easily through a pipe. This can impact the pressure drop within the fuel line and may influence the sizing decision.
When plumbing a fuel system with a mechanical pump and regulator, it is recommended to refer to the pump's specifications for the required fuel line size. If no specific size is listed, it is generally advised to use a -10 (or 5/8") fuel line from the tank to the pump and regulator. The line from the regulator back to the tank can be a size smaller, typically a -8 (or 3/8"). These sizes ensure adequate fuel flow while maintaining proper pressure and gravity feed to the pump.
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Fuel regulator placement
For high-power applications (500+ horsepower), a rapid increase in throttle results in a significant fuel flow rate change, leading to fuel pressure loss between the regulator and the fuel destination. In such cases, placing the regulator closer to the fuel destination reduces pressure loss. Additionally, high-performance diesel applications with a lift pump and an internal regulator can benefit from an external regulator close to the injection pump.
On the other hand, for "lower power" gas or ethanol systems (carbureted or EFI) with moderate flow rates, having the regulator farther from the carburetor, fuel log, or fuel rail does not significantly affect pressure regulation. Similarly, for diesel systems with integrated relief valves, like the FUELAB lift pump systems, pressure differences do not significantly impact performance.
It is worth noting that the type of pump used in the fuel system also influences the regulator placement. Pressure-limited pumps, commonly used with carbureted engines, require a static (non-bypass) regulator, while non-pressure-limited pumps need a dynamic (bypass-style) regulator.
When plumbing fuel lines with a mechanical pump and regulator, consider the specific application and performance requirements to determine the optimal fuel regulator placement. The placement should ensure that the fuel system can provide consistent and adequate pressure to meet the fuel demand.
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Fuel hose material
When plumbing fuel lines with a mechanical pump and regulator, it is important to consider the type of fuel hose material that will be used. The most common fuel hose materials are rubber, nylon, and stainless steel.
Rubber fuel hoses are widely used due to their ease of installation. They are typically connected using standard barbed fittings and fuel line hose clamps. However, rubber hoses have some drawbacks. They start degrading as soon as they come into contact with fuel and, with the exception of J30R9-rated hoses, they will leak fuel vapors, which can be a safety hazard. To address this issue, R9 specification fuel hoses have been introduced, which are designed to withstand pump fuel with ethanol content. These hoses are more expensive but offer better durability and safety by reducing the risk of fuel leaks and fires.
Nylon tubing is another option for fuel line repairs, especially if you are on a budget. It is more durable than plain rubber hose but still has similar issues with long-term durability and fuel vapors.
Braided hose is a variation of rubber hose that has a braided exterior made of stainless steel or nylon. It offers improved durability over plain rubber hose but still faces challenges with fuel vapors.
PTFE-lined hose is the best soft hose available and is usually braided with stainless steel or nylon. The PTFE liner effectively blocks fuel vapors and slows down the degradation process, enhancing the hose's longevity. However, it requires special fittings and is less flexible than standard braided or rubber hoses.
Stainless steel lines have been a traditional choice for automobile manufacturers due to their superior durability compared to soft materials. While metal lines, including those made of stainless steel, aluminum, or coated steel tube, offer excellent performance, they can be challenging to fabricate.
When selecting the fuel hose material, it is essential to consider factors such as compatibility with the type of fuel, ease of installation, durability, and safety. Additionally, the budget and performance requirements of the project will influence the choice of fuel hose material.
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Fuel pump placement
The placement of the fuel pump is a key consideration when plumbing a fuel system. If you are using an electric pump, you could mount it under the car directly in front of the gas tank, as demonstrated by *Car Craft Magazine*. This placement allows for the transmission cooler lines to be routed through the frame to the TCI tranny cooler.
If you are using a mechanical pump, it can be placed on an inner fender well or on the engine. However, engine mounts are sometimes avoided due to fears of vibration messing up the regulator. If you are using a bypass plumbing setup, you may need to fabricate a regulator bracket that mounts to the cylinder heads, as demonstrated by *OnAllCylinders*.
The placement of the fuel pump will also depend on the type of regulator you are using. Most carbureted engines use a deadhead-style regulator, which is placed between the fuel pump and the carburetor. This style of regulator uses a restriction to lower the fuel pressure by decreasing the fuel flow.
If you are using a bypass regulator, it should be placed before the carburetor to help build higher pressure in the feed and counteract the high g-forces experienced during rapid acceleration. This type of regulator is beneficial for carbureted systems as it allows the fuel to circulate consistently, reducing fuel temperatures.
It is important to note that some electric fuel pumps have a regulator built into them, eliminating the need for an external unit. These pumps are typically low-pressure units designed for use with carburetors only. Additionally, most lever-style mechanical fuel pumps do not require a regulator.
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Frequently asked questions
Steel lines, spring clamps, and generic rubber hose have been the plumbing basics for automobile manufacturers. The NPTF (National Pipe Thread Fuel) is typically used on carburettor fuel pumps and some fuel pressure regulators. The thread is tapered, with the female and male thread tightening against each other to form a seal.
Starting from the main fuel tank, plumb the lift pump inside the tank to the surge tank. Then, run a -10 line from the bottom of the surge tank to the inlet of the fuel pump. From the outlet of the pump, use a -10 line to the regulator and then a -6 or -8 line to the carburettor. Finally, run a return line from the regulator back to the top of the tank.
It is recommended to have a surge tank in the front of the car. The line from the surge tank to the main tank should preferably be -10 or -12 to prevent a vacuum. The line should be large enough to allow fuel to travel one way and air to travel the other way. If you need to make a sharp turn, use an angled fitting instead of trying to bend the hose.
The type of fuel can impact the choice of fuel hose. For example, Ethanol can attack rubber compounds used in cheaper fuel hosing, leading to failure. R9 specification fuel hose is recommended for pump fuel with Ethanol content. When choosing components, consider your budget and desired level of performance.
