Understanding Your System Needs

Before buying hoses and fittings, you must understand the specific demands of your engine and catch can setup. The primary role of a catch can system is to capture oil blow-by and contaminants from the crankcase ventilation system before they re-enter the intake. This helps reduce carbon buildup on intake valves, improves engine efficiency, and protects sensitive components like intercoolers and turbos.

Start by identifying your engine type: naturally aspirated, forced induction, or a high-performance build with increased cylinder pressure. Forced induction systems often generate higher crankcase pressures, requiring hoses rated for stronger vacuum and positive pressure. Also consider the operating temperature range. Engine bays can exceed 250°F near exhaust manifolds and turbochargers. Choose hoses that maintain flexibility and structural integrity at those temperatures.

Space constraints matter too. Tight engine compartments may require tighter hose bends, which can restrict flow if the hose collapses. Opt for hoses with reinforcement layers or larger inner diameters to minimize flow restrictions. Additionally, understand your PCV (positive crankcase ventilation) routing: some systems have a dedicated PCV valve, others use a breather setup. The catch can must be integrated correctly to avoid vacuum leaks or excessive pressure buildup.

Finally, determine the connection sizes at the catch can and engine ports. Common sizes range from 3/8″ to 3/4″ inner diameter (ID). Measure the ports precisely to avoid mismatches that cause leaks or difficult assembly.

Choosing the Right Hoses

The hose is the lifeline of your catch can system. It must convey oily vapors and sometimes liquid oil without degrading, collapsing, or bursting. The wrong hose can degrade from fuel and oil contact, crack from heat, or soften under vacuum.

Rubber Hoses

Rubber hoses are the most common and cost-effective choice for standard street engines. They offer good flexibility, easy installation, and adequate chemical resistance to engine oil, fuel vapors, and coolant. Most rubber hoses are made from synthetic compounds like EPDM or neoprene, which resist ozone and weathering. However, standard rubber hoses have a lower maximum temperature rating, typically around 200°F to 250°F. If your engine runs hot or has tight clearances near exhaust manifolds, rubber may soften or degrade over time.

For daily drivers and mild builds, rubber hoses are perfectly adequate. Use reinforced rubber hoses if you need extra wall strength to prevent collapse under vacuum. Rubber is also easy to cut to length and accept standard barbed fittings with hose clamps.

Silicone Hoses

Silicone hoses are the premium choice for high-performance and extreme-temperature applications. They maintain flexibility and strength from -60°F up to 350°F or more, depending on the formulation. Silicone resists oil, ozone, and many chemicals without hardening or cracking. It also handles both high vacuum and low positive pressure (2–5 psi) common in catch can systems.

High-heat silicone hoses are ideal for turbocharged engines, supercharged builds, or any setup where the hose passes near hot components. They also have a smoother inner bore than rubber, resulting in less flow restriction. However, silicone is more expensive and can be less abrasion-resistant than rubber. It also requires special clamping techniques—use constant-tension T-bolt clamps or spring clamps rather than standard worm-gear clamps to avoid cutting the silicone.

Reinforced and Braided Hoses

For extreme crankcase pressures or heavy oil accumulation, reinforced hoses offer structural integrity beyond standard rubber or silicone. Reinforced hoses feature an inner layer of fabric or wire braid embedded in the rubber or silicone. This prevents collapse under high vacuum and resists bursting under positive pressure.

Push-lock hoses (push-on fittings) are a type of reinforced hose with a woven outer layer that grips barbed fittings without clamps. They are common in racing and off-road applications for their leak-free reliability and easy assembly. However, push-lock hoses require specific compatible fittings and can be difficult to disconnect once installed.

Braided PTFE (Teflon) hoses are overkill for most catch can systems but offer the ultimate chemical resistance and temperature range (−60°F to 500°F). They are used in extreme race engines or where every drop of contamination must be prevented. PTFE hoses are expensive and require specialized AN fittings, making them impractical for most street setups.

Hose Sizing and Flow

Hose inner diameter directly affects flow capacity and vacuum draw. A hose that is too small restricts the crankcase ventilation, causing pressure buildup that can force blow-by past piston rings. A hose that is too large can slow vapor velocity, allowing oil to condense and pool in the hose rather than the catch can.

For most naturally aspirated engines up to 500 hp, 3/8″ ID (AN -6) hoses work well. For high-horsepower forced induction engines, use 1/2″ ID (AN -8) or even 5/8″ ID (AN -10) to ensure adequate flow. Always match the hose ID to the catch can and engine ports. When in doubt, use a slightly larger hose; flow can always be restricted at the fitting if needed.

Selecting Fittings

Fittings connect hoses to the catch can, engine valve covers, PCV valves, and intake manifolds. A leak or failure at a fitting can cause unmetered air intake, oil leaks, or performance issues.

Fitting Materials

  • Brass: Brass fittings are corrosion-resistant, easy to machine, and affordable. They work well with rubber and silicone hoses and standard barbed designs. However, brass can be softer than steel, so over-tightening can strip threads or deform the fitting.
  • Stainless Steel: Stainless steel offers superior strength and corrosion resistance, especially in salt-prone or high-humidity environments. It is heavier and more expensive but ideal for long-term reliability in harsh engine bays.
  • Aluminum: Lightweight and resistant to corrosion, aluminum is popular in performance and racing builds. It anodizes easily for color coding. However, aluminum is less tolerant of high torque and can gall threads if not properly lubricated.
  • Nylon/composite: Some budget catch cans use plastic or nylon fittings. These are lightweight and cheap but degrade under heat and UV, crack easily, and should be avoided for any serious build.

Fitting Types

  • Barbed fittings: The most common type for rubber and silicone hoses. Barbs have ridges that grip the inside of the hose, secured with a hose clamp. Available in straight, 45°, 90°, and 180° configurations. Ensure the barb diameter matches the hose ID exactly.
  • AN fittings: Aerospace standard with a 37° flare seal. AN fittings provide a positive, leak-free connection without clamps. They are reusable, come in multiple sizes (e.g., -6 AN = 3/8″), and allow for custom hose lengths with braided or PTFE lines. AN fittings require dedicated wrenches and careful assembly to avoid damaging the flare.
  • Push-lock fittings: Designed for push-lock hose, these have a barbed end with a special serration that grips the hose permanently. No clamp needed. They are very reliable once installed but difficult to remove without cutting the hose.
  • Quick-connect fittings: Used with plastic or composite tubing, quick-connects are push-to-lock and release by pressing a collar. They are convenient on modern OEM-style PCV systems but less common on aftermarket catch cans because they require precise tube sizing and can leak if the O-rings dry out.

Sizing and Thread Compatibility

Fittings have two critical dimensions: the hose end size and the thread size that goes into the catch can or engine port. Catch cans typically use NPT (National Pipe Taper) threads or AN threads, while engine ports may use NPT, BSP, or straight threads with O-rings (e.g., O-ring boss). Always verify thread type and pitch before ordering. Use a thread gauge or consult the manufacturer. Adapter fittings are available to convert between thread standards, but each additional connection is another potential leak point.

Sealing Methods

Proper sealing prevents vacuum leaks and oil drips. For NPT fittings, use PTFE tape (thread seal tape) or pipe thread sealant. Wrap the tape clockwise around the male threads (when facing the fitting end) to prevent shredding during assembly. For AN fittings, no tape is needed—the flare creates the seal. Ensure the sealing surfaces are clean and free of nicks. For straight thread O-ring fittings, replace the O-ring if it shows any damage.

Installation Tips

Routing and Clearance

Plan your hose route to avoid contact with hot surfaces, sharp edges, and moving parts (belts, fans, linkages). Use fire-resistant hose sleeve or heat shield wrap on sections that must pass near exhaust headers or turbo housings. Keep hoses as straight as possible to minimize flow restrictions. If you must make a turn, use a molded 90° fitting rather than kinking the hose—kinks create pressure drops and can cause internal cracking over time.

Clamping

Always use the correct clamp type for your hose material. For rubber hoses, zinc-plated worm-gear clamps work well, but avoid overtightening—you can cut into the rubber or strip the thread. For silicone hoses, use constant-tension T-bolt clamps or spring clamps that maintain pressure through heat cycles. Silicone compresses more than rubber, so a standard clamp can loosen as the engine cools, creating a leak. Position the clamp squarely behind the barb ridge for maximum grip.

Support and Security

Heavy hoses, especially long runs with fluid weight, can put stress on the catch can and engine fittings. Use hose support brackets or P-clips attached to the engine or chassis to take the load off connections. This prevents vibration from loosening fittings and reduces fatigue on barbed ends.

Check for Leaks

After installation, start the engine and let it idle. With the catch can empty, listen for hissing sounds near fittings. Use a smoke machine or soapy water spray to check each joint for bubbles under idle vacuum. If a T-bolt clamp is loose, tighten it. For AN fittings, a small leak may require disassembly, inspection, and retorquing to the specified value.

Maintenance and Inspection

Regular Checks

Inspect hoses and fittings every oil change or every 5,000 miles. Look for cracking, hardening, softening, swelling, or discoloration. Silicone hoses may develop a white powder (ozone cracking) over time—replace them if cracks are visible. Rubber hoses can become brittle in high-heat areas or swell if exposed to gasoline or aggressive cleaning agents.

Leak Detection

Even a pinhole leak in a catch can hose can introduce unmetered air into the intake, causing a lean condition and rough idle. Periodically inspect the engine bay for oil residue around fittings. If you see oily grime near a connection, it indicates a slow leak that will worsen. Tighten or replace the fitting as needed.

Cleaning and Replacement

Over time, hoses accumulate oil sludge and deposits that can clog the system. If you notice reduced crankcase ventilation or increased oil consumption, disassemble and clean hoses with a suitable solvent (e.g., brake cleaner or mild degreaser). Silicone hoses can be washed with soap and water; rubber hoses may degrade with harsh solvents. Replace hoses that show internal flaking or delamination.

Common Mistakes to Avoid

  • Using undersized hoses: Too small a diameter restricts flow, causing pressure buildup that can blow out oil seals or force oil past the rings.
  • Mixing thread types: NPT and AN threads are not interchangeable. Forcing a mismatched fitting can strip threads or create immediate leaks.
  • Over-tightening clamps: This can crush the hose, reduce flow, or cause the hose to fail at the clamp.
  • Routing hoses below the catch can inlet: If a hose dips lower than the catch can inlet, oil can pool in the low spot and clog the system. Always route with a consistent upward slope toward the catch can.
  • Neglecting heat protection: A hose touching a hot surface will fail prematurely. Use heat sleeves or re-route away from heat sources.
  • Skipping check valves: Some catch can setups need a check valve in the PCV line to prevent backflow under boost. Without it, boost can pressurize the crankcase, leading to oil leaks.

Conclusion

Selecting the right hoses and fittings for your Nashville catch can setup is a critical step toward engine longevity and performance. By understanding your engine’s operating conditions—temperature, pressure, flow requirements, and space—you can choose materials and sizes that deliver reliable, leak-free operation for thousands of miles. Rubber hoses with brass barbed fittings suit mild daily drivers; silicone hoses with AN or push-lock fittings handle high-performance and extreme environments. Always verify thread compatibility, use proper clamping techniques, and inspect the system regularly. A well-assembled catch can system not only keeps oil out of the intake but also ensures your engine breathes freely, reducing deposits and extending component life.

For more detailed installation guides and product recommendations, consult trusted sources like Nashville Catch Can, Summit Racing for fittings and hoses, and MotorTrend’s catch can installation guide.