HKS Extension Kit w/ Catalytic Converter - 2013-2021 Subaru BRZ /Scion FR-S/ Toyota 86

Extension Kit with Catalytic Converter for the 2013-2021 FR-S, BRZ, and 86

The HKS Extension Kit with Catalytic Converter for the 2013-2021 Subaru BRZ, Scion FR-S, and Toyota 86 is the front pipe and catalytic converter section that connects the header to the cat-back exhaust system. It is the correct choice for builds using an aftermarket header that requires a specific front pipe to connect to HKS or other cat-back systems. The included catalytic converter maintains emissions compliance while the extension pipe provides the correct connection geometry.

Specs & Highlights

• Front pipe and catalytic converter unit
• Connects aftermarket header to cat-back system
• Emissions compliant catalytic converter
• Correct connection geometry for HKS exhaust systems
• Stainless steel construction
• Fitment: 2013-2021 Subaru BRZ / Scion FR-S / Toyota 86

50.8mm Front Pipe, 400 cpsi Metallic Cat, 40mm Flex Bellows

The extension kit front pipe uses 50.8mm (2 inch) diameter, matching the rest of the HKS FA20 exhaust system diameters. The catalytic converter core is a metallic substrate design with a cell density of 400 cpsi (cells per square inch), which provides lower exhaust back pressure than the OEM ceramic substrate catalyst while maintaining catalytic efficiency above the light-off temperature. The flex joint section uses a 40mm diameter corrugated stainless bellows rated for 10,000+ flex cycles, the primary fatigue concern for any rigid exhaust connection near the engine mount.

Why the Front Pipe Scope Matters for System Consistency

The extension kit is the bridge between an aftermarket header and the cat-back section of the exhaust system. When running equal length headers like the HKS33005-AT006, the factory front pipe and cat section may not connect correctly to the aftermarket header's outlet. The extension kit solves this with the correct pipe geometry and a quality catalytic converter.

Pairs Naturally with HKS Equal Length Headers

Used in combination with the HKS equal length headers and a cat-back or header-back exhaust, the extension kit completes a full HKS exhaust system on the FA20. All HKS exhaust components are engineered to work together and the extension kit ensures the complete system is consistent from header to tailpipe.

The FT Breakdown

The extension kit with cat is the connecting piece for a complete header-back exhaust build on the FA20 FT86. If you are running aftermarket headers and a cat-back, this is what closes the gap between them correctly. The 400 cpsi metallic substrate catalyst in the extension kit is the specification used in OEM performance applications from multiple manufacturers — it provides catalytic efficiency at lower back pressure than the ceramic 600 cpsi converters used in standard replacement catalysts. For a full HKS header-back build where every component is matched for flow, using a high-flow cat at the front pipe is the correct approach.