Why Catch Can Size Matters for Your Engine Build

An oil catch can is a critical component in any performance engine setup, separating oil vapor and blow-by gases from the crankcase ventilation system before they can enter the intake tract. For engine builders and tuners—especially those in the Nashville area where high-horsepower builds are common—selecting the correct catch can size directly affects engine cleanliness, oil consumption, and long-term reliability. A can that is too small will fill quickly, allowing contaminants to reach the intake valves and intercooler, while an oversized can may add unnecessary weight or complicate packaging in tight engine bays.

This guide breaks down the technical factors behind catch can sizing, provides practical recommendations for common Nashville performance builds (LS swaps, Gen III Hemi, Coyote, and turbocharged inline engines), and offers installation tips to maximize the effectiveness of your crankcase evacuation system. By matching catch can capacity to your engine’s specific output and usage, you keep carbon deposits minimal and maintain peak power output.

How Catch Cans Work and Why Capacity Matters

Catch cans sit between the crankcase ventilation outlet (usually on the valve cover or PCV valve) and the intake or air intake tube. As blow-by gases pass through the can, internal baffles, mesh, or a labyrinth design force the oil droplets to condense and collect in the reservoir while the cleaned air continues to the intake. The collected oil is then drained back into the engine (if the system is plumbed for recirculation) or manually emptied.

Capacity matters because the can must hold enough oil during a given service interval to prevent saturation. When the can is full, the internal separator becomes less effective, and liquid oil can be drawn through the outlet, defeating the purpose of the system. In severe cases, a completely flooded catch can can cause a vacuum in the crankcase or restrict ventilation, leading to increased blow-by and even seal damage.

A common mistake is choosing a catch can solely based on physical size rather than its effective oil holding volume. Many “race style” cans have large external dimensions but very little internal capacity due to thick walls or oversized fittings. Always check the actual reservoir volume in ounces or liters when comparing products.

Key Factors That Determine the Right Catch Can Size

Engine Displacement and Configuration

Larger displacement engines produce more blow-by gas because more cylinder volume means more combustion pressure pushing past the piston rings. A 427 cubic inch LS7 naturally aspirated will generate significantly more crankcase vapor than a 4.6L modular V8. For a typical Nashville stroker or big-cubic-inch build, you should plan for at least 2–3 times the catch can capacity compared to a stock-displacement engine.

Engine configuration also matters. V8 engines with high overlap camshafts and high compression produce more blow-by at idle and low RPM than a turbocharged four-cylinder. Rotary engines (though rare in Nashville builds) generate exceptionally high oil vapor volumes and require oversized catch cans.

Induction Type: Naturally Aspirated vs. Forced Induction

Boosted engines present the biggest challenge for crankcase ventilation. Under boost, intake manifold pressure can exceed crankcase pressure, forcing blow-by to escape through the valve cover vents at high volume. A turbo or supercharged engine can easily overwhelm a small catch can during a single pass or dyno pull. For forced induction setups, experts recommend a catch can with at least 32 ounces (1 liter) of effective capacity, and many serious builds use two separate dual-pass cans to handle both bank vents.

Naturally aspirated engines, even those with high compression or aggressive cams, produce less total blow-by and can usually get by with a 16–24 ounce catch can for street use. However, if the engine is revved to 7000+ RPM frequently, increase capacity by 50%.

Driving Conditions and Service Interval

Consider how the vehicle is used. A daily driver that sees stop-and-go traffic and occasional highway cruising will accumulate blow-by oil gradually. An 16-ounce can may need emptying every 3,000–5,000 miles, which is manageable. A dedicated track car or drag car that spends hours at high load will fill a 16-ounce can in a single race day—requiring a larger can or a drain system. For endurance racing or heavy towing applications, a catch can in the 48–64 ounce range allows longer intervals between service.

If you prefer low maintenance or plan to drive long distances without checking fluid levels, oversize your catch can capacity. Many owners find that a 32-ounce can with a clear sight tube is the sweet spot for a weekend warrior LS swapped car used for canyon carving and autocross.

Available Space and Mounting Options

While capacity is important, the catch can must physically fit in your engine bay. In a modern vehicle with tight packaging (like a C5 Corvette or a Fox-body Mustang with a turbo kit), a large can might conflict with air intake plumbing, radiator hoses, or the hood clearance. In such cases, consider using two smaller cans in series (one for each bank) or mounting the catch can remotely with longer hoses. Always mock up the can before finalizing mounting to ensure you can access the drain bung and hoses for maintenance.

Nashville builds often involve engine swaps where bay space is at a premium. A common solution is a compact rectangular catch can (e.g., 4″ x 6″ x 6″) that fits on the inner fender or near the strut tower.

Catch Can Sizing Guidelines for Common Builds

Small Capacity (0–16 oz / 0–0.5L)

Ideal for low-mileage stock Japanese engines, naturally aspirated four-cylinders, or mild V6 engines used for daily commuting. These cans need to be emptied every 1,000–2,000 miles if the engine has high mileage or is worked hard. Not recommended for any performance V8 or forced induction application in a Nashville build.

Medium Capacity (16–32 oz / 0.5–1L)

The most common choice for naturally aspirated LS or LT engines with mild cams, stock displacement, and street use. Also suitable for mild turbo builds on a four-cylinder (e.g., 2JZ-GTE, RB26) if you are willing to drain after each track session. For a typical Nashville daily-driver LS3 swapped with a stage 2 cam, a quality 24-ounce catch can is sufficient for 3,000–5,000 mile intervals.

Large Capacity (32–64 oz / 1–2L)

Recommended for boosted V8s (e.g., 6.0L turbo LS, 5.0L Coyote with supercharger), high-winding naturally aspirated builds (over 6,000 RPM sustained), or large big-block engines. Also ideal for street cars that see occasional drag racing or autocross where you want minimal service attention. A 48-ounce can can easily handle a 1,000 hp TT LS engine for a weekend’s action before needing draining.

Extra Large (64+ oz / 2L+)

Only necessary for extreme high-horsepower builds (1500+ hp) with multiple pressure sources, competition-only vehicles that run frequently at high boost, or marine/industrial applications. For most Nashville high-performance builds, a 64-ounce can is the ceiling. Larger cans become heavy and cumbersome to mount without custom brackets. If you need this volume, consider a closed-loop system with a pump that recirculates oil back to the pan rather than relying on gravity alone.

Calculating Required Capacity for a Specific Build

Basic Rule of Thumb

A simple formula for estimating catch can capacity in ounces: multiply your engine displacement in liters by 4 (for naturally aspirated) or by 8 (for forced induction). Then adjust by a multiplier for driving style:

  • Street daily: 1.0x
  • Street aggressive / occasional track: 1.5x
  • Track/competition only: 2.0x

Example: A 5.3L turbo LS -> (5.3 * 8) = 42.4 ounces. Multiply by 1.5 for street/aggressive -> 63.6 ounces. Round up to 64 ounces. For a mild street driving pattern (1.0x), a 42 oz capacity is safe, so a 48 ounce can would be fine.

Example: Nashville LS6 Swapped C5 Corvette

A common Nashville build: a 5.7L naturally aspirated LS6 with a small cam (220/220 .600 lift) and long-tube headers. Street driven with occasional autocross. Using the NA formula: 5.7 * 4 = 22.8 ounces. Street aggressive multiplier 1.5 -> 34.2 ounces. A 32-ounce catch can would be borderline; a 36–40 ounce can would give margin. In practice, a quality 32-ounce unit with good baffling will work if emptied every 2,000 miles on the street and after each track day.

For a comparison, visit Summit Racing’s guide on catch can sizing for additional examples.

Beyond Capacity: Other Crucial Catch Can Features

Baffling Efficiency

A catch can’s internal design matters as much as its volume. Look for multiple chambers, a fine mesh filter, or a cyclone separator. Cans that rely solely on gravity (just a hollow container) allow liquid oil to be pulled back into the intake under high flow. The best designs create a pressure drop and multiple directional changes to separate oil from air. Always open a catch can before buying to inspect the baffle quality—especially for the price range common in Nashville speed shops.

Vented vs. Sealed Systems

Vented catch cans release pressure to atmosphere (often with a small filter). While legal in non-emission-controlled environments, they can create a mess and are not allowed on OBDII vehicles in some states. Sealed catch cans connect both inlet and outlet to the intake system, maintaining a closed PCV loop. For Nashville builds that must pass emissions (or just want a clean engine bay), sealed cans are preferred. Ensure the catch can has a vacuum port compatible with your PCV system.

Construction Materials

Aluminum is standard, but check for smooth interior surfaces without sharp edges that can trap oil or form sludge. Anodized finishes resist corrosion better than paint. Avoid steel cans unless they have an internal coating—rust particles can cause severe engine damage. For high-heat engine bays (especially turbo builds), look for catch cans with a powder coating that handles 300°F+.

Drain Valve and Sight Glass

A petcock drain (like an oil pan drain) makes emptying much easier during oil changes or after a race. Some catch cans feature a clear sight tube so you can monitor fluid level at a glance—very helpful for maintaining confidence in the system. If you choose a can without a sight glass, install a manual dipstick or check it regularly by weight.

Mounting and Routing for Optimal Performance

Mount the catch can as low as possible, but above the highest oil level in the engine. A lower mount reduces the risk of siphoning oil from the can back into the engine when it’s full. Route the PCV hose to the catch can inlet and use the outlet to connect back to the intake (or to a vacuum source on boosted setups). Use high-temperature silicone hoses with proper fittings to prevent collapse under vacuum. For dual-valve cover setups, use a Y-connector to merge both vents into one catch can inlet.

Check out JEGS’ installation guide for step-by-step photos relevant to many LS swaps.

Conclusion

Choosing the right catch can size for your Nashville engine setup is a balance of engine displacement, induction type, driving use, and available space. While a 32-ounce catch can covers many street and mild performance builds, turbo and high-RPM naturally aspirated setups typically require 48–64 ounces for safe intervals. Beyond capacity, pay attention to internal baffling, sealing, material quality, and drain convenience. A well-selected catch can protects your intake valves from carbon buildup, reduces oil in the intercooler, and keeps your crankcase ventilation functioning as intended.

Recent industry testing confirms these guidelines—see EngineLabs’ article on catch can sizing for dyno data on different capacities. With the right setup, your Nashville-built engine will breathe cleanly and deliver reliable performance for years to come.