The 3 Best PLM Catalytic Converters for Your Honda Civic Si

The Honda Civic Si is a tuner favorite for its K-series engine and responsive chassis. One of the most effective power upgrades is replacing the restrictive factory unit with an aftermarket catalytic converter. A high-flow cat reduces backpressure for gains in horsepower, torque, and throttle response.

Considering a new catalytic converter can cost $1,000 or more, a high-performance upgrade offers significant value. Private Label MFG (PLM) leads with quality catalytic converters for the Civic Si. This guide breaks down the top PLM options for your build.

Beyond performance, upgrading can be a strategic move. Catalytic converter thefts increased by over 300% nationwide from 2019 to 2022, with the replacement cost to vehicle owners averaging over $2,500. A welded aftermarket unit serves as both a performance upgrade and a theft deterrent.

1. PLM Power Driven High-Flow Metallic Converter - Best for Maximum Horsepower

For maximum performance, the PLM 200-Cell High-Flow Cat is the undisputed champion. Its low-density metallic core and straight-through design dramatically reduce exhaust restriction.

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With a defouler or proper ECU tune, it often avoids triggering the check engine light (CEL), making it ideal for weekend racers and performance enthusiasts.

Key Features

• 200-cell high-flow metallic substrate for massive flow increase
• 2.5 in. inlet/outlet with CNC-machined flanges for leak-free seal
• Stainless steel shell with TIG welds for strength and corrosion resistance

Pros

This delivers the most noticeable horsepower and throttle-response gains of any standalone cat upgrade, felt immediately in acceleration and mid-range power. Durable stainless steel construction ensures long-term reliability. Installation is straightforward: it bolts directly between your header and exhaust with basic hand tools.

Cons

This part is not CARB certified and is intended for off-road or track use only, making it illegal for street use in California and CARB-compliant states. The increased flow also produces a noticeably louder, more aggressive exhaust note that may be too loud for quiet daily driving.

2. PLM High-Flow 400-Cell EPA Metallic Converter - Best for 49-State Street-Legal Driving

If you want to improve performance on your daily-driven Civic Si without worrying about passing emissions tests, the PLM 400-Cell EPA Metallic Converter is the ideal choice. It strikes a perfect balance between enhanced flow and emissions compliance.

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While the power gains are more modest, this unit is engineered to meet EPA standards for 48 states, providing improved performance, enhanced durability over the OEM ceramic unit, and crucial peace of mind during inspections.

Key Features

• 400-cell metallic core engineered to meet EPA standards while flowing better than stock
• 2.5 in. tubing with stainless steel shell for durability and corrosion resistance
• Easy "cut-and-clamp" or weld-on installation

Pros

Designed for emissions compliance outside of California, this converter provides a worry-free upgrade with noticeable improvements in engine breathability and response. The exhaust note remains close to stock, perfect for stealthy performance enhancement without attracting attention.

Cons

This unit still cannot be legally used on registered vehicles in California. The performance improvement is also not as dramatic as the race-oriented 200-cell version, with more modest power gains.

3. PLM Power Driven 3-Way Adjustable Catalytic Converter - Best Budget & Versatility

The PLM 3-Way Adjustable Catalytic Converter is an engineered solution for builders working on multiple projects or complex engine swaps.

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Its unique multi-orientation flange can be rotated and locked into three different positions. This versatility allows a single part to fit a wide range of Honda chassis, including the 8th-gen Civic Si, base model Civics, and even some Acura RSX setups. It’s the ultimate problem-solver for budget-conscious builders who need adaptability without compromising on performance.

Key Features

• Multi-orientation flange with locking plate for perfect fitment across different header and exhaust combinations
• 200-cell metallic core with 2.5 in. diameter for excellent power gains
• Extra O₂ bung for installing a wideband O₂ sensor without modifying the exhaust

Pros

The unmatched versatility makes this a go-to for K-swaps and custom builds, with one part fitting several Honda/Acura platforms. This saves money during engine swaps or header changes by eliminating the need to buy a new catalytic converter. The added bung for a wideband sensor is a premium feature that simplifies the tuning process and data logging.

Cons

The adjustable flange mechanism adds a small amount of weight compared to fixed-flange models. On some specific aftermarket header combinations, a shim or extra gasket might be needed to achieve a perfect seal due to the adjustable design.

Quick Comparison: Which PLM Cat Is Right for You?

Still unsure which catalytic converter fits your needs? This quick comparison highlights the key differences between all three PLM options to help you make the right choice based on your driving style and performance goals.

Unlock Your Civic Si's True Potential

Upgrading your catalytic converter is one of the most cost-effective modifications for real performance gains. Whether you need maximum horsepower, street-legal compliance, swap versatility, or an all-in-one solution, PLM has a proven option for your build.

Don't let a restrictive factory cat hold back your Civic Si's performance. With PLM's proven quality, competitive pricing, and comprehensive warranty coverage, there's no reason to wait. Choose your upgrade today and feel the difference that unrestricted exhaust flow makes on your next drive.