What Is an APEXi Catch Can and Why Does Your Subaru WRX Need One?

The Subaru WRX is a turbocharged, high-performance machine, but its boxer engine layout and modern direct-injection system create a unique challenge: oil vapor contamination in the intake tract. An APEXi Catch Can is an aftermarket device designed to capture those oil vapors and combustion byproducts before they recirculate into your engine’s intake. By doing so, it helps keep your valves, intercooler, and turbocharger cleaner, which can lead to more consistent performance and reduced carbon buildup.

Factory Subaru engine ventilation systems route blow-by gases from the crankcase back into the intake manifold (via the PCV valve) and the intake tube (via the breather hose). While this meets emissions standards, it also dumps oil mist directly into the airstream. Over time, this oil coats the intake valves, intercooler cores, and turbo blades, causing loss of power, knock, and even premature engine wear. Installing an APEXi catch can intercepts that oil before it causes trouble.

The Problem with Oil Vapors in Your Intake

Direct-injection engines like the FA20 and FA24 in newer WRX models do not have fuel washing over the intake valves. This means any oil vapor that condenses on the valves becomes baked into hard carbon deposits. Even earlier EJ-series WRX engines suffer from this issue, albeit with some fuel cleaning effect from port injection. The result is the same: reduced airflow, knock sensitivity, and lower horsepower as deposits accumulate.

A catch can does not stop blow-by from happening, but it separates the oil and condensate from the air. The cleaned air continues back to the intake, while the captured liquid stays in the can for periodic disposal. This simple step can dramatically slow carbon buildup and keep your engine running at peak efficiency.

How a Catch Can Works

An APEXi catch can uses internal baffles and a coalescing medium (like stainless steel mesh) to force oil droplets to coalesce and fall to the bottom of the can. The cleaned air exits through a separate port and returns to the intake system. The APEXi design is compact, easy to mount, and includes clear sight lines so you can see how much oil it collects. It is a passive device—no moving parts, no electronics—just pure mechanical filtration.

Tools and Parts Required for Installation

Before starting, gather these items. Having everything ready makes the job faster and reduces the chance of mistakes.

  • APEXi Catch Can kit (with mounting bracket, hoses, clamps, and fittings)
  • Socket set (10mm, 12mm, 14mm)
  • Combination wrenches
  • Flathead and Phillips screwdrivers
  • Hose cutters or a sharp utility knife
  • Drill with a step bit (if bracket requires new holes)
  • Zip ties and wire loom
  • Shop rags and a drip pan
  • Safety glasses and gloves

Some Subaru WRX models may require additional adapters if the stock PCV fitting is incompatible. Check the APEXi product listing or your vehicle’s specific year (2015+ FA20, 2022+ FA24, or EJ series) to confirm compatibility. A set of silicone vacuum caps and extra vacuum hose (3/8″ or 5/8″ as needed) can be useful for custom routing.

Step-by-Step Installation Guide

Perform this work on a cold engine to avoid burns and to prevent hot oil from spraying. Work in a well-ventilated area.

Step 1: Prepare Your Engine Bay

Park the car on a level surface and open the hood. Locate the stock crankcase ventilation system. On a WRX, you’ll find a hose running from the passenger side of the engine (near the turbo inlet) and another from the driver side (near the PCV valve on the intake manifold). Take photos or mark the hoses to remember their routing. Disconnect the negative battery terminal for safety.

Step 2: Remove the Factory PCV and Breather Hoses

Using pliers or your hands, carefully release the factory spring clamps from the hoses. Slide the hoses off their barbed fittings. Some oil may drip out—keep rags handy. Note that the PCV hose typically attaches to a plastic nipple on the intake manifold; this nipple can be brittle, so use gentle pressure. If the hose is stuck, gently twist it back and forth while pulling.

You do not need to remove the PCV valve itself unless you plan to replace it (recommended every 60,000 miles). Simply disconnect the hose from the valve and set it aside. The breather hose from the crankcase to the intake tube is usually larger; remove it from both ends.

Step 3: Mount the Catch Can

Choose a mounting location that is secure, accessible for draining, and away from hot exhaust manifolds or moving belts. Common spots on a WRX include the strut tower brace area, the inner fender well, or the bracket behind the passenger headlight. APEXi includes a mounting bracket; position it and mark the holes. If drilling is required, use a step bit and install a rivet nut or bolt into a solid metal surface. Avoid plastic panels or thin sheet metal. Secure the can using the supplied hardware and tighten to hand-torque.

Step 4: Connect the Hoses Correctly

This is the most critical part. You are routing the incoming dirty air from the engine (crankcase) to the catch can, and the outgoing clean air from the can back to the intake system. Do not reverse the flow direction—APEXi marks the ports as “IN” and “OUT.”

Attach the hose from the PCV valve (or the crankcase breather on the driver side) to the “IN” port. Attach the other end of the “OUT” port to the original intake hose location, or directly to the intake manifold if you are using a dual-can setup. Use new clamps and tighten them enough to prevent leaks but not so much that you cut the hose. If your WRX has two crankcase vents (one from each head), consider using two catch cans or a single dual-port unit. Many owners successfully use one can on the PCV side and leave the breather side open to atmosphere with a small filter—check local emissions laws before doing this.

Route the hoses away from heat sources and sharp edges. Use zip ties or wire loom to secure them and prevent chafing. Ensure that the hoses do not kink or bend sharply; gravity should allow oil to drain into the can, so try to maintain a downward slope from the engine to the can.

Step 5: Final Checks and Leak Testing

Double-check all connections. Reconnect the battery. Start the engine and let it idle. Listen for any hissing sounds indicating a vacuum leak. Spray a small amount of soapy water around each connection—bubbles indicate a leak. Tighten clamps as needed. Let the engine reach operating temperature and rev it gently. Check again for leaks. Shut off the engine and inspect the catch can for proper orientation; the drain valve should be easily accessible.

If you notice a strong oil smell or the engine runs rough, you may have a vacuum leak or hose routing error. Common mistakes include connecting the can in the wrong direction or failing to cap unused ports on the intake. Ensure that any factory ports not used are plugged with a vacuum cap.

How Much Power Does an APEXi Catch Can Add?

The short answer: no direct horsepower gain from the catch can alone. However, the real benefits are in preserving power and reducing knock. By keeping oil out of the intake, you maintain the engine’s designed airflow and combustion efficiency. Over time, this means your WRX retains its peak power and responds better to modifications.

On a stock WRX, you might see a slight improvement in throttle response and part-throttle driveability after installing a catch can, but a dyno would show negligible peak power change. The real power gain comes when the intake valves stay clean—dyno tests on carbon-cleaned direct-injection engines have shown recoveries of 10–20 horsepower after valve cleaning. A catch can prevents that buildup, so you avoid the power loss in the first place.

Real-World Dyno Results and Owner Experiences

Examples from Subaru forums (like NASIOC and SubaruForester.org) show that owners who track their oil catch volume often collect 50–100 mL of oil per 3,000 miles. That’s oil that would otherwise be coating your intake. After a year, the difference in intake condition is dramatic. Some tuners report that cars with catch cans require less aggressive knock control and maintain ignition timing better under load, which translates to safer, more consistent power.

For a modified WRX (bigger turbo, higher boost), the catch can becomes even more important. Oil vapor increases with horsepower, so the can captures more contaminants and keeps the intercooler and piping clean. In those builds, a catch can is often considered mandatory for reliability.

Maintenance and Emptying Your Catch Can

APEXi catch cans have a drain valve or a removable bottom cap. Check the can every oil change (3,000–5,000 miles) or more often if you drive aggressively. To empty, place a container under the drain, open the valve, and let the collected oil and condensate drain out. Dispose of it at a recycling center. If the can has a clear sight tube, you can check the level visually. Never let the can fill completely, as this can allow oil to be sucked back into the intake.

Occasionally inspect the hoses for cracks or softening over time. Replace them if they feel hard or brittle. Some owners clean the can’s internal baffles annually by rinsing with brake cleaner or isopropyl alcohol.

Catch Can vs. Air Oil Separator (AOS): Which Is Better for Your WRX?

Both devices reduce oil in the intake, but they work differently:

  • APEXi Catch Can (air/oil separator) is passive and typically requires manual draining. It does not return oil to the engine, so you lose a small amount of oil volume between changes. It is simpler and cheaper.
  • Air Oil Separator (AOS) actively returns the separated oil to the oil pan via a drain line, so no oil is lost. It often includes a heater to prevent freezing in cold climates. AOS units are more expensive and more complex to install.

For most street-driven WRX owners in moderate climates, a catch can is sufficient. For those who drive in extreme cold or want zero maintenance, an AOS might be better. However, APEXi catch cans are well-regarded for their build quality and ease of maintenance. You can also run both a catch can on the PCV side and an AOS on the breather side if you want the best of both worlds.

Common Installation Mistakes to Avoid

  • Mixing up inlet and outlet. Always route crankcase gasses into the “IN” port.
  • Using too long or too short hoses. Hoses should be long enough to avoid stress but not so long that they sag and collect oil puddles.
  • Mounting the can upside down. The APEXi can’s design requires the inlet/outlet to be above the collection chamber. Read the instructions.
  • Forgetting to plug the intake tube. If you disconnect the breather hose, you must cap the intake tube nipple or install a small filter; otherwise, unmetered air enters the system, causing a lean condition.
  • Skipping the leak check. A vacuum leak from a loose clamp can cause rough idle and reduced power. Take the five extra minutes to verify.

Conclusion

Installing an APEXi Catch Can on your Subaru WRX is one of the smartest preventative modifications you can make. While it won’t add explosive horsepower on paper, it preserves the power you already have and extends the life of critical engine components. The installation is straightforward with basic hand tools, and the ongoing maintenance is minimal. For more details, refer to the official APEXi USA product page and check community guides on SubaruOutback.org for model-specific tips. Keep your intake clean, your valves carbon-free, and your WRX running strong for thousands of miles to come.