Understanding the Purpose of a Catch Can

Modern engines rely on a Positive Crankcase Ventilation (PCV) system to manage blow-by gases that slip past the piston rings. These gases contain oil vapors, unburned fuel, and combustion byproducts. Without a catch can, these contaminants are routed back into the intake tract, where they can coat intake valves, intercooler cores, and throttle bodies. Over time, this buildup causes reduced airflow, loss of power, and poor fuel economy. For Nashville-based builds that see both stop-and-go city traffic and high-demand highway pulls, a custom catch can system becomes a vital upgrade to protect engine internals and maintain peak performance.

A well-designed catch can holds the oil and condensed vapors, allowing only clean air to re-enter the intake. This simple mechanical intervention can extend the life of your engine, especially in direct-injection (DI) vehicles where there is no fuel spray to wash the intake valves. While many production cars come with basic PCV systems, they often lack the capacity or separation efficiency needed for modified engines. Customization ensures your system matches your specific combination of displacement, boost levels, and driving style.

Key Components of a Custom Catch Can System

The Catch Can Container

The heart of your system is the container itself. Choose a unit with a baffled interior or a coalescing filter to separate oil mist from air. Common materials include polished aluminum, stainless steel, or billet aluminum. These resist corrosion and handle under-hood temperatures easily. Capacity matters: for a typical V8 or boosted four-cylinder, a 500ml to 1-liter can is sufficient. For high-output engines or dual-can setups, larger options are available. Look for ports sized to match your existing PCV hose diameter (usually 10mm to 19mm ID). Many aftermarket cans include a dipstick, sight glass, or quick-drain valve for easy monitoring.

Hoses and Fittings

Use oil-resistant hose rated for high temperatures, such as push-lock silicone or reinforced rubber (e.g., Aeroquip or Earl’s). Avoid basic vacuum line, which can collapse or degrade. Barbed fittings with O-ring seals are reliable, though AN-style fittings offer a cleaner look and easier disconnection. Plan for a minimum of two 90-degree elbows if routing is tight. Ensure all clamps are constant-tension or automotive-grade worm-gear style to prevent leaks. For forced induction applications, consider high-pressure-rated hose that will not bulge under boost.

Breather Vent or Return Valve

Some systems route the clean air back into the intake (closed system), while others vent to atmosphere (open system). In a closed system, a one-way check valve (PCV valve) prevents boost from pressurizing the crankcase. For open systems, a small breather filter on the catch can allows clean air to escape but can produce a mild oil smell. In Nashville, where emissions testing is required in some counties, a closed system that recirculates air may be necessary to pass visual inspections. Research local laws before choosing.

Mounting Bracket and Hardware

Your catch can needs a solid, vibration-free mount. Use stainless steel or powder-coated steel brackets that attach to existing bolt holes on the fender, firewall, or strut tower. Ensure the can is upright and that the outlet port is higher than the inlet to promote gravity drainage. Leave enough clearance to remove the can for emptying. Consider adding rubber isolation grommets between the bracket and chassis to reduce noise transmission.

Design Considerations for Nashville Builds

Nashville’s climate and driving mix create unique demands. Summers are hot and humid, causing higher oil temperatures and increased vapor formation. Winters are milder but can bring damp conditions that accelerate condensation inside the catch can. Stop-and-go traffic on I-440 or I-65 generates more blow-by at low RPM, while enthusiastic driving on backroads or the Tail of the Dragon requires a system that can handle sustained high RPM without becoming a restriction. Below are specific design strategies for naturally aspirated and forced induction builds.

For Naturally Aspirated Engines

NA engines generate moderate crankcase pressure. A single catch can with a 3/8-inch or 10mm inlet is typically adequate. Place the can as close to the valve cover as possible to catch oil immediately after it exits the engine. Use a dedicated PCV port on the valve cover (or a tapped fitting) for the cleanest route. If your engine has two valve covers (V6 or V8), consider a dual-can setup or a single large can with dual inlets. Avoid using the oil filler cap as a vent unless you install a baffled cap. For Nashville’s humidity, a can with a condensate drain at the bottom is beneficial. Many NA owners report improved throttle response and less intake fouling after installation.

For Forced Induction Engines

Boosted builds (turbo or supercharged) create much higher crankcase pressure, especially under load. Oil vapor can be forced backward through the PCV system into the intake, causing intercooler oil buildup and potential detonation. A dual-catch-can setup is common: one can for the PCV (dirty side) and one for the fresh air line (clean side) that normally vents clean air into the valve cover. Alternatively, use a single large can with high-efficiency baffling. Ensure all hoses and fittings are rated for boost pressure – many standard catch cans fail when subjected to 15+ PSI. Install the catch can after the intercooler but before the throttle body on the clean side to keep oil out of the induction system. Use a one-way check valve that opens under vacuum and closes under boost. In Nashville’s hot summers, intercooler efficiency drops, so reducing oil contamination becomes even more important to maintain knock protection.

Step-by-Step Installation Tips

Step 1: Plan your routing. Trace the existing PCV system. Identify the hose from the valve cover to the intake manifold (usually 3/8” or 5/8”). Also locate the fresh air inlet hose from the air cleaner or turbo intake to the valve cover. Decide whether you will install one or two catch cans.

Step 2: Choose mounting location. Pick a spot where the can stays cool (away from exhaust headers) and is accessible for periodic draining. Common locations: passenger side strut tower, firewall behind the engine, or a bracket attached to the intake manifold. Use a metal bracket that can be painted or powder-coated to match your build.

Step 3: Disconnect the battery. While not strictly necessary, it’s good practice when working near electrical components. Remove the existing PCV hose.

Step 4: Install fittings and hoses. Cut hose to length, allowing for a slight upward loop to prevent liquid from pooling. Install barbed fittings into the catch can ports (inlet and outlet). Use hose clamps at every connection. For AN fittings, use wrenches to tighten but do not overtighten aluminum fittings. If adding a second can, label each hose to avoid confusion.

Step 5: Connect inlet and outlet. The inlet hose comes from the valve cover PCV port; the outlet goes to the intake manifold or to atmosphere (if open system). For boosted engines, install the check valve in the line between the can and the intake manifold, with the arrow pointing toward the intake. Ensure the valve can handle the temperature range.

Step 6: Verbally check for leaks. With the engine running, listen for hissing. Use a spray bottle of soapy water to check fittings. A small leak can cause a lean condition and rough idle. Also verify that the PCV valve (if retained) is functioning.

Step 7: Test drive and monitor. Take a short drive and let the engine reach operating temperature. Stop and inspect the can for any collected oil. If the can is bone dry after 50 miles, the system may not be properly vented or you may have connected the lines backward.

Maintenance and Troubleshooting

Routine Maintenance Schedule

  • Every 1,000 miles or after each track event: Check the catch can fluid level. Empty if more than half full. Dispose of oil properly.
  • Every 5,000 miles: Inspect all hoses for heat damage, cracking, or swelling. Replace as needed. Clean or replace the internal baffle if accessible.
  • Every 10,000 miles: Remove the catch can and clean the interior with brake cleaner. Check the one-way check valve for proper operation (should only flow one direction).
  • Seasonally: In Nashville’s winter, condensation can freeze inside the can if left full. Drain before frost.

Common Troubleshooting Issues

Excessive oil in can after short drives: This could indicate a worn PCV valve, excessive ring blow-by, or a baffle issue in the valve cover. Check compression and leak-down numbers. Also verify you haven’t reversed the inlet and outlet – the inlet should come from the crankcase.

No oil collected after 500 miles: The system may be inoperative. Check for vacuum leaks at the intake manifold connection. If the engine has high vacuum at idle, there should be a slight suction at the can outlet. If not, the check valve might be stuck closed or installed backward.

Oil smell inside cabin: This usually means the vent is too close to a fresh air intake or the can is leaking vapors. Ensure all clamps are tight and the can has a sealed drain. For open systems, move the breather filter location away from cabin air intake.

Check engine light after installation: Some engines monitor PCV flow. A closed system with a properly functioning PCV valve should not trigger a code. If the light appears, check for large vacuum leaks or a disconnected MAF sensor wire.

Conclusion

Designing a custom catch can system for your Nashville build is a rewarding upgrade that protects your engine from oil contamination and improves long-term reliability. By selecting quality components – a baffled can, robust hoses, and correct fittings – and tailoring the design to your engine type and local driving conditions, you create a system that performs consistently. Regular maintenance keeps it effective for years. Whether you drive a daily commuter on I-24 or a weekend track car at Nashville Superspeedway, a custom catch can is a smart investment. For further reading on PCV system theory, check out Summit Racing’s catch can selection guide or Jegs’ comprehensive product range. For technical insights on direct injection carbon cleaning, see MotorTrend’s article on DI carbon buildup.