What Are The Best Catalytic Converters for Honda B-Series?

The Honda B-Series, whether it's the high-revving B16 or the torque-rich B18, is a legend in the import scene. It’s a durable, responsive, and endlessly tunable platform. 

However, after you’ve installed a cold air intake, exhaust headers, and aftermarket exhaust, one major bottleneck is holding you back: the factory catalytic converter.

The original component was designed to reduce harmful emissions, not maximize power, and after two decades of service, it’s likely tired and restrictive. 

If you're experiencing limited flow, check engine lights for P0420 codes, or rattles from a broken internal structure, it is time for an upgrade.

Let's find the perfect cat for your build.

Catalytic Converter Buying Guide for Honda B-Series

Choosing the right catalytic converter isn't just about slapping on the shiniest part. It's about matching fitment, flow, and legal requirements to your specific car and goals. Here’s what you need to know before you buy.

Fitment Basics

The B-Series was used in various chassis and came with different OBD (On-Board Diagnostics) systems, which directly impact cat fitment. The most common difference is the flange orientation between the header and the cat.

System / Chassis	Common Years	Key Fitment Notes
OBD I	1992-1995	A simpler system often has a more direct flange angle.
OBD II	1996-2001	Requires two O2 sensor bungs (pre-cat and post-cat).
Integra (DC2)	1994-2001	Generally uses a longer catalytic converter than Civic models.
Civic (EG/EK)	1992-2000	Uses a shorter converter. Using an Integra cat requires a custom-length mid-pipe.

Always double-check if your header outlet uses a 2-bolt or 3-bolt gasket before ordering.

Flow vs. Compliance

The core of a catalytic converter is a ceramic honeycomb measured in cells per square inch (CPSI). Lower CPSI means better flow and more power, but potentially less emissions control.

• 400 CPSI (OEM Standard): Excellent emissions reduction, but more restrictive. Ideal for daily drivers in strict states.
• 200 CPSI (High-Flow): The sweet spot for performance. Offers a significant reduction in backpressure, unlocking 4-6 horsepower on average over a stock unit, without the raw fumes of a test pipe.

Compliance is non-negotiable. Here's a quick reference:

• CARB-Compliant: The strictest standard, required for cars registered in California and other states that follow its rules. These parts have an Executive Order (EO) number.
• EPA 49-State Legal: Legal for use in all states except California. These meet federal emissions standards.
• Race-Use Only: Not legal for use on public roads. These include test pipes and some ultra-high-flow cats.

Materials & Construction

Build quality directly impacts how long your investment will last.

• Stainless Steel: The premium choice. Offers superior corrosion resistance, strength, and longevity. Heavier than aluminized steel, but will likely outlast the car.
• Aluminized Steel: A budget-friendly option that offers decent corrosion resistance but is more susceptible to rust in harsh climates or areas with road salt.

A manufacturer's warranty is a huge indicator of their confidence in the product's durability.

Budget & Brand Checklist

Before you click "buy," run through this final checklist:

1. Price: Does the cost align with the materials and compliance offered?
2. Warranty: Is there a solid warranty (2+ years) to protect against defects?
3. Proven Performance: Does the brand provide dyno charts or real-world data?
4. Community Reputation: What are other B-Series owners saying on forums and social media?

Key Insight: The core decision isn't just about brands; it's a trade-off between maximizing power with a high-flow cat (200 CPSI) and ensuring legality with a compliant one. Know your state's laws first.

Top Catalytic Converters

PLM Power Driven High Flow Performance Metallic Catalytic Converter

Snapshot Rating: ★ 4.7/5 | Price Tier: $$

Pipe Diameter	2.5" / 3.0"
Material	Metallic Metal Core
Core CPSI	200
Compliance	OBD-II compliant 48-state legal (Restricted in CA and NY)
Warranty	1 Year

Pros: Easy "cut-and-clamp" or weld-on installation, stainless steel construction, includes the highest quality 200-cell

Cons: Restricted in CA and NY.

Fitment Notes: This aftermarket catalytic converter is available for both OBD I (2-bolt) and OBD II (3-bolt) B-Series headers. Precise lengths for Civic and Integra chassis ensure a bolt-on fit with no modification needed. The O2 bung is angled perfectly to avoid contact with the heat shield.

CHECK PRICE

PLM High Flow Performance 400 Cell Metallic Catalytic Converter

Snapshot Rating: ★ 5/5 | Price Tier: $$

Pipe Diameter	2.5" / 3.0"
Material	Stainless Steel, Metallic Core
Core CPSI	400
Compliance	OBD-II compliant 48-state legal (Restricted in CA and NY)

Pros: Balances emissions control with improved flow, durable metallic substrate resists heat/vibration, includes O2 bungs and hardware for bolt-on installation.

Cons: Not CARB-compliant for CA or NY.

Fitment Notes: Perfect for OBD I/II B-Series in Civic EG/EK and Integra DC2 chassis. Bolt-on design with precise lengths. No modifications needed.

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PLM Power Driven 3-Way Adjustable Catalytic Converter

Snapshot Rating: ★ 4.8/5 | Price Tier: $$

Pipe Diameter	2.25” / 2.5" / 3.0"
Material	3-Way Catalytic, Stainless Steel
Core CPSI	200
Compliance	OBD-II compliant 48-state legal (Restricted in CA and NY)

Pros: Most common fitment for Honda & Acura vehicles, quick bolt-on installation, most common fitment for Honda & Acura vehicles.

Cons: Not CARB compliant.

Fitment Notes: Universal fitment. Verify the part number for your exact chassis before buying. Includes all necessary flanges and hangers.

CHECK PRICE

Installation & Fitment Tips

Replacing a faulty catalytic converter can result in a successful installation, meaning no exhaust leaks and no check engine lights. Prepare with the right parts and follow the right procedure.

• Required Parts: Always use new gaskets. Most leaks come from reusing old, crushed ones. You'll likely need a header-to-cat gasket (2 or 3-bolt) and a donut gasket for the cat-to-midpipe connection. Get fresh M10 x 35mm bolts and spring bolts as well.
• Use Anti-Seize: Apply a small amount of copper-based anti-seize to all bolt threads and O2 sensor threads. This will save you a massive headache years down the road.
• O2 Sensor Placement: Install the oxygen sensors before bolting the cat to the car. Ensure the wires are not twisted or stretched.
• Torque Specs: Overtightening can warp flanges and crush gaskets. 

Follow these general specs:

Header to Cat Bolts (M10)	~33 ft-lbs
Cat to Mid-Pipe (Spring Bolts)	~16 ft-lbs

CEL Prevention: The O2 Spacer Trick. On OBD II cars, a high-flow cat can sometimes cause a P0420 (Catalyst System Efficiency Below Threshold) code. An angled O2 sensor spacer (or defouler) pulls the secondary O2 sensor slightly out of the direct exhaust stream, tricking it into seeing a cleaner reading. This modification is intended for off-road use and may not be legal in your area.

Pro Tip: After your first drive (about 100 miles), let the exhaust cool down and re-torque all the bolts. The initial heat cycles can cause them to loosen slightly.

Important: Never reuse old exhaust gaskets. The few dollars you save will cost you hours chasing down frustrating and performance-robbing exhaust leaks. Always start with fresh hardware for a seal.

Why Upgrading Your B-Series Catalytic Converter Matters

A stock catalytic converter is designed for emissions efficiency, not maximum power, and after two decades of service, it’s likely tired and restrictive.

If you're experiencing any of these issues, it's time for an upgrade:

• Limited Flow: Your stock cat is choking your engine's potential, especially on modified setups.
• Check Engine Lights (CEL): An old, inefficient converter can trigger annoying P0420 codes.
• Degradation: The internal honeycomb structure can break down, causing rattles or complete blockages.

Upgrading to a high-flow catalytic converter can unlock lost horsepower, improve throttle response, and ensure your modified B-Series runs as efficiently as possible.

Maintenance, Break-In & Longevity

A new catalytic converter needs a proper break-in to ensure the internal matting sets correctly and the catalyst is fully activated. 

Additionally, the efficiency of a catalytic converter can degrade over time due to contamination, overheating, and physical damage, making proper maintenance crucial.

Heat-Cycle Break-In:

1. Start the engine and let it idle for 5 minutes.
2. Turn off the engine and let it cool completely for at least 30 minutes.
3. Repeat this process two more times.

Watch for signs of premature failure, which are usually caused by an engine issue:

• Rattling Noise: The internal core has broken apart, often from excessive vibration or physical impact.
• Sulfur (Rotten Egg) Smell: Indicates the engine is running too rich, and unburnt fuel is overheating the converter.
• Loss of Power: A clogged or melted core is creating a massive exhaust restriction.

Myth-Buster: Can you clean a clogged catalytic converter? No. The "clog" is often a melted or broken internal structure. Pressure washing or using additives is a temporary fix at best and can damage the precious metal coating, making it useless for emissions control.

Important: A new cat can't fix an underlying engine issue. Misfires or a rich condition will quickly destroy any converter, leading to a melted core. Ensure your engine is healthy first.

Final Recommendations

Choosing the best catalytic converter for your B-Series comes down to a simple trade-off: balancing maximum performance with street legality. Understanding the difference between OEM and aftermarket car parts is crucial. OEM converters prioritize emissions compliance, while aftermarket options like PLM focus on flow and power gains.

• Best Overall (EPA States): PLM High Flow Performance 400 Cell Metallic Catalytic Converter for a superior balance of flow and compliance.
• Best Performance: PLM Power Driven High Flow Performance Metallic Catalytic Converter for proven power gains and stainless construction.
• Best Street-Legal: PLM Power Driven 3-Way Adjustable Catalytic Converter (verify EO# for your state).

Before you make a final decision, always check your local regulations. When you're ready to unlock your B-Series' true potential, explore PLM's full lineup of precision-engineered exhaust components.

Shop our full lineup of B-Series exhaust components with free shipping and lifetime support.