Fuel Line Choices for EFI Conversions

Embarking on a fuel injection conversion for a classic vehicle like a '69 Nova presents a fantastic opportunity to modernise performance and drivability. However, when it comes to the fuel supply lines, particularly for the higher pressures associated with fuel injection, many enthusiasts find themselves in uncharted territory. The question of the most painless and economical fuel supply line to build often arises, with braided lines and those featuring crimp connections being common points of discussion. This article delves into the various options available, offering insights into their suitability, cost, and assembly, to help you make an informed decision for your small-block Nova project.

Understanding Fuel Line Requirements for EFI

Fuel injection systems operate at significantly higher pressures than traditional carburettor setups. While a carburettor might be content with around 5-7 psi, Electronic Fuel Injection (EFI) systems typically demand pressures in the range of 40-60 psi, with some performance applications pushing even higher. This increased pressure necessitates fuel lines and fittings that are specifically designed to handle these demands safely and reliably. Failure to use appropriate components can lead to leaks, fuel starvation, and potentially dangerous situations. The lines must also be resistant to modern fuel formulations, which often contain aggressive additives like ethanol that can degrade older rubber compounds.

The Premium Option: Convoluted PTFE Fuel Hose

For those seeking the ultimate in fuel line performance and longevity, the latest offerings in convoluted Polytetrafluoroethylene (PTFE) fuel hose, such as Earl's UltraPro, represent the pinnacle. PTFE, a material akin to Teflon®, is inherently resistant to all known fuels and fuel additives, ensuring compatibility and preventing degradation over time. A crucial advancement in modern PTFE hose is the incorporation of carbon impregnation. This carbon additive makes the inner liner conductive, thereby eliminating the risk of static electricity build-up and discharge – a potential hazard with non-conductive PTFE. This conductivity is a requirement for many modern vehicles, contributing to their lower evaporative emissions.

The convoluted design of this hose offers a significant advantage: flexibility. Unlike straight PTFE hose, the ribbed or convoluted structure allows for tighter bend radii without kinking or compromising the internal flow. This makes routing the lines much easier, especially in the often-cramped confines of a classic car's chassis. The near-perfect vapor barrier properties of PTFE also mean minimal fuel evaporation, which is not only environmentally beneficial but also contributes to consistent fuel delivery. As such, this type of hose is what you'll find specified in most modern OEM (Original Equipment Manufacturer) vehicles.

However, this premium performance comes at a premium price. The specialised fittings required for convoluted PTFE hose utilise a sealing ferrule and demand a specific, albeit not overly complex, assembly procedure. This involves sliding the ferrule onto the hose before carefully attaching the fitting. While the upfront cost for both the hose and fittings can be substantial – with a 20-foot length of 3/8-inch (-6 AN) UltraPro hose costing upwards of $180 and individual fittings around $25 – the longevity and reliability are often considered a worthwhile investment, potentially lasting the lifetime of the vehicle.

Key Features of Convoluted PTFE Hose:

• Material: Carbon-impregnated PTFE for fuel resistance and conductivity.
• Design: Convoluted for increased flexibility and tighter bend radii.
• Performance: Excellent vapor barrier, minimal evaporation.
• Durability: Highly resistant to modern fuel additives and heat.
• Fittings: Requires specific fittings with a sealing ferrule.
• Cost: High initial investment.

The Middle Ground: Non-Convoluted PTFE Hose

Companies like TechAFX also offer PTFE hose, often in a non-convoluted, smooth bore configuration. While still benefiting from the inherent fuel resistance and vapor barrier properties of PTFE, the lack of convolution means this hose is stiffer and requires larger bend radii. This can make routing more challenging in tight spaces compared to its convoluted counterpart. Similar to the convoluted PTFE, these hoses also require specialised fittings that use a ferrule for a secure seal, and the assembly procedure is largely the same.

The Economical Choice: Multi-Layer Rubber Hose

For those more budget-conscious, Earl's Vapor Guard hose presents a significantly more affordable alternative. This hose features a multi-layer rubber construction designed to withstand the aromatic additives commonly found in modern fuels and provides a degree of vapor barrier protection. While Earl's does not explicitly state the inner liner material, it is generally understood not to be PTFE. The good news is that the associated fittings are far less expensive. These are typically simple, slip-on barbed fittings that are secured with high-quality hose clamps.

The Vapor Guard hose is available in versions specifically designed for carburettor or EFI applications. It is absolutely critical to use the EFI-specific hose, which is rated to handle a maximum fuel pressure of 225 psi. The carburettor-only version, rated to only 50 psi, is entirely unsuitable for EFI systems, even at the lower end of the pressure spectrum.

While the Vapor Guard hose offers a cost-effective solution, it may not offer the same long-term durability or resistance to extreme heat as PTFE-based hoses. Furthermore, it's important to be aware of regulations. For instance, NHRA drag strip tech rules limit the use of uncovered rubber fuel hose to a total length of 12 inches on a vehicle. In such cases, a covered hose, such as braided stainless steel with a rubber lining, or the premium PTFE options, would be necessary to pass inspection. The Vapor Guard hose, being an uncovered rubber hose, would likely not meet these requirements.

Vapor Guard Hose Considerations:

• Material: Multi-layer rubber, not PTFE.
• Cost: Significantly more affordable than PTFE.
• Fittings: Simple barbed fittings secured with hose clamps.
• Pressure Rating: Ensure use of the EFI-rated hose (225 psi max).
• Durability: Potentially less durable in extreme heat or long-term use compared to PTFE.
• Regulations: May not comply with certain racing or institutional rules regarding uncovered rubber hose.

Braided Stainless Steel Hose

Often seen in custom builds, braided stainless steel hose is another popular option. Typically, these hoses consist of a reinforced inner liner (often synthetic rubber or sometimes PTFE) covered by a protective layer of braided stainless steel. The stainless steel braiding offers excellent abrasion resistance and a clean, professional appearance. Like PTFE hoses, braided stainless steel hoses usually terminate with AN fittings that require a specific crimping or swaging process, or they utilise reusable fittings that clamp onto the hose after it's slid over a barb.

The advantage of braided stainless steel is its robust physical protection and its aesthetically pleasing look. The inner liner material is key; a PTFE liner will offer the best fuel resistance, while a rubber liner might be more susceptible to degradation over time, especially with aggressive fuel additives. The fittings for braided hose can vary, from crimp-on types that require specialised tools to reusable AN fittings that screw onto the hose after it's positioned over a barb. The latter can be more convenient for DIY builders but might not offer the same inherent security as a permanently crimped connection.

Fitting and Assembly: The Crucial Details

Regardless of the hose material chosen, the fittings are equally important. For EFI conversions, using the correct size and type of AN (Army-Navy) fittings is standard practice. For a 3/8-inch fuel line, a -6 AN fitting is typically used. The connection method is where the types of hose diverge:

• PTFE Hoses (Convoluted and Non-Convoluted): These require specialised fittings that incorporate a sealing ferrule. The assembly involves carefully sliding the ferrule onto the hose, ensuring it's positioned correctly, and then threading the fitting onto the hose, which compresses the ferrule to create a seal. This method provides a very robust and leak-free connection.
• Multi-Layer Rubber Hoses (e.g., Vapor Guard): These use simple barbed fittings. The hose is slid over the barbed end of the fitting, and a high-quality hose clamp (often a worm-gear style or a specialised EFI clamp) is tightened around the hose to secure it to the barb and create a seal. While simpler, the quality of the clamp and the tightness of the seal are paramount.
• Braided Hoses: Depending on the type of fitting, assembly can involve crimping (requiring specialised hydraulic or pneumatic tools) or screw-on reusable fittings. Reusable fittings typically involve sliding a nut and then the ferrule over the hose, pushing the hose onto the fitting's barb, and then screwing the nut down to capture the ferrule and create the seal.

Comparison of Fuel Line Options:

Recommendations for your '69 Nova

For your '69 Nova with a small-block and an EFI conversion, the choice hinges on your priorities: budget, ease of installation, and long-term performance.

• If budget is not the primary concern and you want the best: Opt for the convoluted PTFE hose (like Earl's UltraPro). Its flexibility will make routing easier in your classic Nova, and its inherent properties offer unparalleled fuel resistance and longevity. The slightly higher cost for fittings is a small price to pay for the security and performance.
• If you need a balance of cost and performance: Consider braided stainless steel hose with a PTFE liner. This offers good flexibility, excellent fuel resistance, and a visually appealing, protected finish. Ensure you use high-quality fittings, whether crimp-on or reusable, and follow the manufacturer's instructions meticulously.
• If budget is a major constraint: The Earl's Vapor Guard EFI hose is a viable option. However, you must be absolutely certain to purchase the EFI-rated hose and use appropriate, high-quality hose clamps. Be mindful of any potential racing regulations if you plan on attending track events. For a street-driven car where budget is paramount, this is a sensible choice, provided it's installed correctly.

When it comes to the question of tightening a fuel pump liner, it's important to clarify that fuel pump liners themselves are typically not "tightened" in the way one might tighten a bolt. Instead, the fuel pump assembly usually sits within a housing or a sock (a pre-filter). The pump is often secured by O-rings or seals within this housing to prevent bypassing. If the reference is to securing the fuel line to the pump outlet, then the process involves attaching the appropriate fitting to the fuel pump's outlet port using the specified method – be it a threaded connection, a compression fitting with a ferrule, or a barbed fitting with a clamp, depending on the pump and line system being used.

Frequently Asked Questions

Q1: Can I use standard rubber fuel hose from an auto parts store for my EFI conversion?
A: Absolutely not. Standard rubber fuel hose is not designed to withstand the higher pressures or the chemical composition of modern fuels used in EFI systems. Using such hose is a serious safety risk.

Q2: What does '-6 AN' mean?
A: '-6 AN' refers to the size of the fitting and hose. AN fittings are measured in sixteenths of an inch. So, -6 AN corresponds to a 6/16ths of an inch (or 3/8ths of an inch) nominal inside diameter. This is a common size for EFI fuel systems.

Q3: Do I need special tools to install AN fittings?
A: For crimp-style AN fittings, yes, specialised hydraulic or pneumatic crimping tools are required. For reusable AN fittings, basic hand tools like wrenches and Allen keys are usually sufficient, along with a good vice or hose holding tool.

Q4: How do I ensure my fuel line installation is safe?
A: Always use components specifically rated for EFI applications. Ensure all connections are tight and properly sealed. Secure the fuel lines properly to the chassis to prevent chafing or movement. Double-check for any leaks after installation by running the fuel pump with the engine off (listen for the pump and check for drips). Consider using a fuel pressure gauge to verify system pressure.

Q5: Is braided stainless steel hose always lined with PTFE?
A: Not always. Braided stainless steel hose can be found with various inner liner materials, including different types of synthetic rubber. For EFI applications, a PTFE or a fuel-specific synthetic rubber liner is highly recommended for optimal compatibility and longevity.

Choosing the right fuel line for your EFI conversion is a critical step. By understanding the properties and requirements of different hose types and fittings, you can ensure a safe, reliable, and high-performing fuel system for your classic Nova.