Fuel Line Buyer's Guide
Fuel lines carry fuel from your tank to your fuel system components including your pump, filter, and fuel rail, and back again in return-style systems. Fittings are the connectors that join those lines to each component. Selecting the right combination of line size, material, and fittings is critical to prevent leaks and ensure your fuel system can reliably support your target horsepower. This guide walks you through everything you need to know to plumb your fuel system right the first time.
Why Upgrade Fuel Lines?
Stock fuel lines are adequate for most vehicles. But as horsepower and fuel demand increase, factory plumbing can become a bottleneck. Common reasons to upgrade include:
- Significantly Increasing Horsepower: More power requires more fuel. Upgrading your fuel lines ensures your factory lines do not become a bottleneck to your fuel system.
- Switching to E85: Since E85 requires 30-40% more volume for the same power output, which may exceed what your stock lines can supply.
- Converting to EFI: Modern fuel injection systems operate at higher pressure. Older lines designed for carbureted application are not rated for these pressures and must be replaced.
Fuel Line Kits vs. DIY
Before selecting individual components, decide whether a fuel line kit or a custom DIY build is right for your application.
Fuel Line Kits
Vehicle/engine specific kits provide a complete, engineering solution for a given application. Benefits include:
- Guaranteed fit: All fittings, diameters, and thread pitches are pre-matched. No adapters needed.
- Correct lengths: Lines are pre-cut or measured for your chassis's factory routing, reducing the risk of lines that hang too low or rub against moving parts.
- Simplified installation: Kits often include specialized mounting hardware and fittings that make installation easy.
A kit is the right choice if you're upgrading a specific vehicle for the first time and want a predictable install with all components included.
DIY / Custom Plumbing
Building a custom fuel system from bulk hose and individual fittings gives you complete control over routing, sizing, and materials. This is the better path for:
- Builds where no kit exists for your application.
- High-performance or race builds requiring custom routing or exotic materials.
- Builders who want to optimize cost by sourcing components individually.
The rest of this guide covers everything you need to build a custom system from scratch.
How a Fuel System Is Plumbed
A fuel system has two distinct plumbing segments: rigid hard lines that run the length of the vehicle, and flexible hoses that bridge the engine bay and fuel tank connections.
Hard Lines
Hard lines carry fuel across the length of the chassis. They are typically made from steel, stainless steel, or aluminum and are resistant to road debris, heat, and degradation over time. Because of their rigidity, hard lines are ideal for long chassis runs but difficult to fabricate and flare without specialized tools. For this reason, they are usually purchased pre-bent for a specific application rather than custom-built.
Flexible Hoses
Hard lines run until they reach the engine bay or the fuel tank. Because engines shift on their mounts and fuel tanks can flex, a rigid metal line cannot connect directly to these components. Flexible hoses absorb vibration and movement at these junctions and are the most common upgrade point in a performance fuel system.
Hose Materials
In automotive fuel systems, the most common fuel line materials are rubber, CPE, and PTFE. Your choice in material determines its pressure rating, chemical compatibility, and fitting options.
Rubber (SAE J30R7 / J30R9)
Rubber fuel hoses are the budget option and are available in two pressure ratings:
- J30R7: Rated to 50 PSI. For carbureted systems only. Not suitable for EFI.
- J30R9: Rated to 100 PSI. Suitable for fuel-injected street vehicles.
Rubber hoses suffer from limited lifespans compared to synthetic alternatives, they degrade with exposure to ethanol fuel blends, and they allow fuel vapors to permeate through the walls. Rubber lines use push-in fittings or clamps.
CPE (Synthetic Rubber)
CPE is common in many performance builds. It uses synthetic rubber reinforced with a stainless steel braid, with an optional nylon sleeve for abrasion resistance. CPE is flexible, easy to route, and significantly more durable than standard rubber. Unless the manufacturer specifically notes E85 compatibility, CPE should not be used in vehicles running E85 or methanol. These fuels attack the synthetic rubber and reduce its service life. CPE lines use push-lock or swivel AN fittings.
PTFE (Teflon)
PTFE is the gold standard for high-performance applications due to its durability, chemical resistance, thermal stability, and ability to prevent gas odors. The one downside of PTFE is that the line is prone to kinking when bent, so be careful during routing/installation. Use angled fittings when needed to avoid tight bends. PTFE lines must use PTFE-specific AN fittings.
Fuel Line Sizing
The inner diameter of your fuel line determines maximum flow rate and, therefore, the maximum horsepower your fuel system can support. The automotive industry uses the AN (Army-Navy) standard for performance plumbing. The AN number represents the inner diameter in 1/16-inch increments.
Below are guidelines regarding the maximum horsepower a certain fuel line size can support on gasoline. Keep in mind these are just guidelines. Your pump, filter, and fuel type will determine the real number. If you are running E85, expect your max horsepower to be lower for a given line size because of the 30-40% additional fuel volume that E85 requires.
| AN Size | Inner Diameter | Approx HP (Gas) |
|---|
| AN-5 | 5/16" | Up to ~350 hp |
| AN-6 | 3/8" | Up to ~550 hp |
| AN-8 | 1/2" | Up to ~1000 hp |
| AN-10 | 5/8" | Up to ~1500 hp |
When sizing your system, all hoses, fittings, and components should share the same AN size throughout. Mismatched sizes require adapters and introduce flow restrictions.
Fittings
Fittings join fuel lines to components in your fuel system. The fitting you choose must match both your hose material and hose size. Using the wrong fitting type is one of the most common causes of fuel leaks.
AN Fittings
AN fittings are the performance standard because they are modular, available in many sizes and angles, and easy to service or reconfigure. Fuel systems typically use anywhere from AN-5 to AN-12, depending on the fuel flow required. AN fittings are available in a wide range of angles including straight, 45°, 90°, 120°, 180°, allowing you to navigate complex routing without stressing the hose.
When shopping, pay attention to the connection type and size of both ends. Many fittings serve as adapters between AN and other standards (metric, ORB, barb, etc). Always verify the connection type on each end before purchasing fittings.
Push-Lock Fittings
Push-lock fittings use internal barbs to create a secure, clamp-free seal. They're quick to install and work with rubber or CPE hoses, but they are only rated for low pressure systems (less than 100 psi). Clamps can be added on top of push-lock fittings for extra insurance.
Swivel Fittings
Swivel fittings allow the hose to rotate 360° during and after installation, making them ideal for tight spaces where a fixed fitting might kink the line. Compatible with CPE hoses only.
Quick Disconnect
Quick disconnect fittings allow for tool free connection and disconnection. They can be great options when you frequently need to remove or service lines.
Other Fittings
Other fittings include hard-line fittings, weld-in fittings, fittings to seal unused ports, and the standard barb fitting seen commonly on vacuum lines. Barb fittings always require hose clamps to secure the connection.
Conclusion
Plumbing a fuel system correctly is as important as the components themselves.
- Match line diameter to your horsepower target. When in doubt, size up. Larger lines never hurt flow.
- Match hose material to your fuel type. If you run E85, PTFE is the only safe choice.
- Match fittings to your hose material. Rubber lines use push-in fittings or clamps, CPE lines push-lock or swivel AN fittings, and PTFE lines use PTFE-specific fittings.
- Keep the whole system consistent. Use the same AN size at every connection point to avoid adapters and restrictions.
If a vehicle-specific kit exists for your application, it's the most reliable starting point. For everything else, use the specifications in this guide to select and size your custom system with confidence. You can find all the parts you need and plan your build on RideBuilder.
Additional Resources
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