Why Forced Induction Demands a Better Catch Can Setup

Forced induction engines—whether turbocharged or supercharged—place far more stress on the crankcase ventilation system than naturally aspirated motors. Under boost, intake manifold pressure can exceed crankcase pressure, reversing the normal flow of the PCV system. This forces oil-laden vapors into the intake tract, where they coat intercoolers, throttle bodies, and intake valves. The result is knocked-out octane, increased detonation risk, and progressive carbon buildup that robs power and compromises engine longevity.

A standard catch can may work for mild street cars, but a properly customized Nashville catch can system is essential for any forced induction vehicle that sees hard pulls, track days, or daily Nashville traffic. By tailoring the catch can’s size, baffling, drainage, and routing to your engine’s specific boost curve, you turn a simple oil separator into a critical performance component.

Understanding the Nashville Catch Can System in a Boosted Context

The Nashville catch can system is more than just a container with two hose barbs. At its core, it relies on three principles: condensation, impingement, and gravity separation to pull oil mist and vapors out of the crankcase gases. For forced induction, the system must handle higher flow rates, more volatile pressure differentials, and the risk of drawing boost into the crankcase through a malfunctioning PCV valve.

Key Differences for Forced Induction

  • Higher blow-by volume: Boost increases cylinder pressure, forcing more combustion gases past the rings. A larger or more efficient catch can is needed.
  • Pressure reversal under boost: The PCV valve closes under boost, but the system must still vent crankcase pressure to atmosphere or a vacuum source. A dedicated check valve or one-way breather becomes critical.
  • Oil vapor condensation in intercoolers: Oil coating the intercooler core reduces heat transfer efficiency and can create hot spots. Catching oil before the intake is even more important on boosted setups.
  • Increased risk of detonation: Oil in the intake mixture lowers the effective octane rating. A good catch can reduces this risk significantly.

For a deeper dive into crankcase ventilation theory, see this Engine Builder Magazine article on crankcase ventilation.

Key Components to Customize for Boost

Every component of your catch can system can be optimized for forced induction. Below are the areas that deserve the most attention.

Catch Can Size and Internal Baffling

Size matters more under boost. A can that is too small will fill quickly, and the internal air velocity will be too high to allow oil droplets to drop out of suspension. Look for a can with at least 1-quart capacity for daily boosted street cars, and up to 2 quarts for high-horsepower applications.

Internal baffling is even more important. Avoid simple “coffee can” designs with no internal structure. The best catch cans for forced induction use a combination of:

  • Stainless steel mesh or coalescing media to catch fine oil mist.
  • Vertical baffle plates or swirl chambers to force the air to change direction abruptly, dropping out heavier oil droplets.
  • A drain-back valve at the bottom (some designs allow oil to drain back to the oil pan under vacuum, though this is controversial on boosted cars).

Port Size and Configuration

Most catch cans come with -8 AN or -10 AN barbed ports. For engines making 500+ hp, consider moving to -10 AN or even -12 AN to reduce restriction. Dual inlet ports can also help balance crankcase pressure on V-configurations by pulling equally from both valve covers.

Check Valves and One-Way Breathers

Under boost, the PCV valve slams shut. But the crankcase still needs to vent. The standard approach is to install a one-way breather on the clean-side (intake-tube) connection, so that boost cannot pressurize the crankcase through the catch can. Many customizable kits include a dedicated check valve that can be placed in the hose between the intake tube and the catch can outlet. For a complete guide on check valve placement, read this Hot Rod article on catch can installation.

Drain Valve and Sight Tube

Forced induction engines produce more blow-by, so you will drain the can more often. A ball valve or petcock at the bottom allows quick draining without disconnecting any hoses. Adding a clear sight tube that runs from the bottom port up the side of the can lets you see the oil level at a glance—essential for preventing overflow.

Mounting Location Considerations

Heat is the enemy of oil separation. If you mount a plastic or even aluminum catch can directly on a hot valve cover, the internal temperature will stay high, reducing condensation efficiency. Instead, mount the can in a location where it receives airflow:

  • Low in the engine bay near the inner fender, but protected from road debris.
  • Away from exhaust manifolds and turbo heat shields.
  • Accessible for quick draining—don’t bury it under the intake manifold.

Use rubber isolation mounts to reduce vibration transmitted to the can, which can shake oil back into the air stream.

Step-by-Step Customization Guide for Forced Induction

Follow these steps to create a custom Nashville catch can system that handles boost like a champ. Note that each vehicle’s PCV layout varies, so adapt these steps to your specific engine (LS, Coyote, EJ, etc.).

  1. Assess your existing PCV system. Identify the fresh-air inlet (pre throttle body) and the crankcase outlet (valve cover or PCV valve). For boosted cars, the PCV valve is often removed or replaced with a breather. Note hose sizes and routing.
  2. Select your catch can with forced induction in mind. Choose a can with at least 1 quart capacity, internal baffling (mesh or labyrinth), and either -8 AN or -10 AN ports. Many companies like Mishimoto and Radium Engineering offer dedicated boosted catch can kits.
  3. Decide on a “vented” vs “sealed” system. Vented cans release pressure to atmosphere via a breather filter, but this can cause oily fumes under the hood and may not be street-legal in some areas. Sealed systems route the outlet back to the intake pre-turbo, but require a check valve to prevent boost from pressurizing the crankcase. For most street-driven forced induction cars, a sealed system with a check valve is recommended.
  4. Plan hose routing with gravity in mind. Run the inlet hose from the valve cover or PCV port to the top of the catch can. The outlet should exit from the top or side (depending on can design) and route via a check valve to a vacuum source (usually the intake tube pre-turbo). Keep hoses as short as possible, but avoid sharp bends that can trap oil.
  5. Install the catch can and all fittings. Use brass or aluminum barbed fittings, not plastic. Apply a small amount of high-temp RTV or Teflon tape to threaded connections, but keep it away from the hose barbs. Secure the can with brackets that keep it stable but allow easy removal for cleaning.
  6. Add a drain valve and sight tube. If your can doesn’t come with one, install a 1/4-turn ball valve at the bottom. For the sight tube, use clear reinforced vinyl hose rated for oil and at least 200°F.
  7. Pressure test the system. Start the engine and let it idle. Feel all hoses and fittings for leaks. Check that the check valve is oriented correctly (flow direction arrow). Rev the engine to see if the catch can remains stable and doesn’t suck closed.
  8. Perform a road test and inspection. Drive the car under boost (street or dyno). After a few pulls, check the can for oil accumulation. Adjust hose routing if any kinks appear. Listen for any hissing that indicates a vacuum leak.

Advanced Customization Tips for Maximum Performance

Using a Dedicated Vacuum Source

For high-boost applications, the standard intake tube connection may provide insufficient vacuum to pull vapors out of the crankcase efficiently. Consider integrating a vacuum pump or connecting the catch can outlet to a dedicated port on the intake manifold (post-throttle body) through a restrictor. This creates a strong, consistent vacuum that improves oil separation and reduces parasitic losses from pressurized crankcase. However, ensure you include a check valve to prevent boost from entering the crankcase at wide-open throttle.

Dual Catch Cans for Big Power

Engines making over 700 wheel horsepower often benefit from two catch cans: one for the PCV (dirty side) and one for the fresh air inlet (clean side). The clean-side can catches oil that gets pushed out the breather line and prevents it from coating the compressor wheel or intercooler. Both cans should be drained regularly.

Selecting High-Temp Hoses

Under-hood temperatures near a turbo or supercharger can exceed 300°F. Standard rubber vacuum hose will degrade quickly. Use braided AN hose with PTFE liner or silicone hose rated for 350°F+. Silicone is flexible and resists oil degradation, but should be routed away from direct contact with exhaust components.

Adding a Breather Tank for Track Days

If your car sees heavy track use, consider replacing the catch can with a small breather tank that has a built-in oil separator and a large diameter vent to atmosphere. This prevents any risk of pressurizing the crankcase under sustained high RPM, which can blow out seals. Many road race and drag cars use this setup, though it may not be emissions-legal.

Regular Maintenance: The Key to Longevity

A customized catch can only work if it is maintained. With forced induction, check the can every 500–1000 miles during normal driving, or after every track day. Drain the accumulated oil into a proper container and dispose of it responsibly. If the can fills completely, oil will be carried directly into the intake, defeating the purpose entirely.

Every 6 months, disassemble the catch can (if possible) and clean the internal baffles with brake cleaner or a solvent. Replace any hoses that show signs of cracking or swelling. Inspect check valves for proper operation by blowing through them in both directions—they should only flow one way.

For more insights on forced induction PCV systems and catch can tuning, check Super Street Online’s thorough guide.

Conclusion

Customizing your Nashville catch can system for forced induction vehicles is not just about slapping on a cheap oil separator. It requires choosing the right capacity, internal baffling, port sizes, check valves, and mounting location to cope with the unique pressures and volumes that boost creates. By following the steps above—and understanding the science behind crankcase ventilation—you can protect your engine from oil contamination, reduce carbon buildup, and maintain consistent power output. Whether you’re daily driving in Nashville or hitting the strip, a well-designed custom catch can system will pay dividends in engine health and performance.

Invest in quality components, maintain your system diligently, and you’ll keep your forced induction engine running strong for years to come.