Catalyst / Bypass
- Porsche Boxster 986 2.5L 1997-99
- Porsche Boxster 986 2.7L 1999-02
- Porsche Boxster S 986 3.2L 1999-02
- Porsche Boxster 986 2.7L 2003-04
- Porsche Boxster S 986 3.2L 2003-04
- Porsche Boxster 987 2.7L 2005 -08/08
- Porsche Boxster 987 S 3.2/3.4L 2005-08/08
- Porsche Boxster 987 MKII 2.9L 2009-2012
- Porsche Boxster S 987 MKII 3.4L 2009-2012
- Porsche Boxster 981 2.7L 2012-16
- Porsche Boxster 981 S / GTS 3.4L 2012-16
- Porsche Boxster 981 Spyder 3.8L 2016

Fits:
Porsche Boxster 986
Click 'Zoom in' for large parts diagram.
Diagram ref no 26
Related reference numbers
Related, superseded, cross reference or alternative numbers for comparison.
90015100703
The product you are viewing cross references to these numbers
- Porsche Boxster 986 2.5L 1997-99
- Porsche Boxster 986 2.7L 1999-02
- Porsche Boxster S 986 3.2L 1999-02
- Porsche Boxster 986 2.7L 2003-04
- Porsche Boxster S 986 3.2L 2003-04
PORSCHE BOXSTER 2.7L & 3.2L S Replacement Type Approved Petrol Cats made in grade 409 stainless steel. Recommend to change in a pair
Fits:
Porsche Boxster 986 2.7L / 3.2L
Note: You will need M8x1x10 Plug (9000838000) & M8x11.5 Seal ring (90012305020) from each original Cat or suitable replacement
A catalytic converter is an emissions control device to stop harmful exhaust gasses from entering the atmosphere. In 1993, they became legality in the UK as part of the Euro Emissions standards. The aim of them is to improve air quality. As emissions standards have become more stringent the number of cats on a vehicle has increased. Many vehicles now have two or more to enable them to meet the Euro Emissions standards.
Our cat is made up of the following components:
• Ceramic monolith of a honeycomb design to allow free air flow and maximum surface area, coated with precious metals to enable the conversion of gasses that pass through it
• Interam matting to hold the monolith in place. The matting expands when exposed to heat to supply the pressure needed to keep the monolith secure
• A grade 409 stainless steel can (or housing) to provide protection and enable the cat to be built into the exhaust system. 409 grade can contain upto 90% iron and will be prone to rust. It still has higher rust-resistant properties than mild steel.
Related reference numbers
Related, superseded, cross reference or alternative numbers for comparison.
99611302
The product you are viewing cross references to these numbers
- Porsche Boxster 986 2.7L 1999-02
- Porsche Boxster S 986 3.2L 1999-02
- Porsche Boxster 986 2.7L 2003-04
- Porsche Boxster S 986 3.2L 2003-04

Porsche Boxster 2.5L Replacement Cats made in grade 409 stainless steel. Recommend to change in a pair
Fits:
Porsche Boxster 986 2.5L
Note: You
will need M8x1x10 Plug (90021901500) & M8x11.5 Seal ring (90012305020) from
each original Cat or suitable replacement
A catalytic converter is an emissions control device to stop harmful exhaust gasses from entering the atmosphere. In 1993, they became legality in the UK as part of the Euro Emissions standards. The aim of them is to improve air quality. As emissions standards have become more stringent the number of cats on a vehicle has increased. Many vehicles now have two or more to enable them to meet the Euro Emissions standards.
Our cat is made up of the following components:
- Ceramic monolith of a honeycomb design to allow free air flow and maximum surface area, coated with precious metals to enable the conversion of gasses that pass through it
- Interam matting to hold the monolith in place. The matting expands when exposed to heat to supply the pressure needed to keep the monolith secure
- A grade 409 stainless steel can (or housing) to provide protection and enable the cat to be built into the exhaust system. 409 grade can contain upto 90% iron and will be prone to rust. It still has higher rust-resistant properties than mild steel.
Related reference numbers
Related, superseded, cross reference or alternative numbers for comparison.
99611392
The product you are viewing cross references to these numbers
- Porsche Boxster 986 2.5L 1997-99

Fits:
Porsche Boxster 986
Diagram ref no 25
Related reference numbers
Related, superseded, cross reference or alternative numbers for comparison.
99950741308
The product you are viewing cross references to these numbers
- Porsche Boxster 986 2.5L 1997-99
- Porsche Boxster 986 2.7L 1999-02
- Porsche Boxster S 986 3.2L 1999-02
- Porsche Boxster 986 2.7L 2003-04
- Porsche Boxster S 986 3.2L 2003-04
Exhaust Catalytic Converters & Bypass Pipes – Performance, Efficiency & Flow Control
The catalytic converter plays a crucial role in your Porsche’s exhaust system, reducing harmful emissions while maintaining optimal exhaust flow. Positioned between the exhaust manifold and silencer, it converts toxic gases such as carbon monoxide, hydrocarbons, and nitrogen oxides into less harmful emissions before they exit the tailpipe.
At Design911, we offer a complete range of catalytic converters and bypass pipes for Porsche vehicles. Our manufacturer-quality converters ensure reliable emission control and long-term performance, while our bypass options are designed for track or performance use, optimising exhaust flow for maximum power and throttle response.
Whether you’re maintaining your Porsche to meet emissions standards or upgrading for improved exhaust performance, our selection includes both direct-fit converters and performance bypass kits built from high-grade stainless steel for strength, corrosion resistance, and durability.
What Do Catalytic Converters & Bypass Pipes Do?
A catalytic converter uses a fine mesh of precious metals to trigger chemical reactions that break down pollutants. The bypass alternative eliminates restriction in the exhaust flow, improving performance in non-emissions-controlled environments such as track driving.
Core Functions:
- Converts
toxic exhaust gases into environmentally friendly emissions.
- Maintains
exhaust back pressure for engine efficiency.
- Reduces harmful NOx, CO, and HC emissions.
- Supports smoother engine performance and throttle control.
- Bypass versions enhance exhaust flow and improve power output for track cars.
Upgrading to a performance-grade system ensures your Porsche continues to meet emission requirements — or achieves greater flow and responsiveness for motorsport applications.
Why Do Catalytic Converters Fail?
Catalytic converters are exposed to extreme heat, unburnt fuel, and contaminants — all of which can degrade their performance over time.
Common Causes of Failure Include:
- Carbon
or oil buildup blocking the internal honeycomb.
- Thermal
damage from overheating or rich fuel mixtures.
- Physical
damage from road debris or misfiring engines.
- Corrosion
due to moisture and exhaust condensation.
- Age-related wear reducing catalytic efficiency.
A failing converter can cause reduced engine power, poor
fuel economy, rattling sounds, or a check-engine light. Replacing it
restores emissions compliance, performance, and exhaust efficiency.
Why Replace or Upgrade
with Precision-Engineered Components?
Replacing a failing converter or upgrading to a bypass pipe ensures your Porsche maintains peak performance and reliability.
Key Benefits:
- Restores optimal emissions performance and efficiency.
- Improves exhaust flow and throttle response.
- Reduces engine stress and fuel consumption.
- Durable stainless-steel construction for longevity.
- Direct-fit
compatibility for Porsche 911, Cayman, Boxster, Panamera, Macan
and more.
- Performance bypass options available for track and tuning applications.
Whether you want emissions compliance or maximum flow for competition use, our parts deliver reliability, precision, and performance.
Highlights:
- Direct-fit catalytic converters and bypass pipes for Porsche models.
- Precision-engineered for optimal flow and reduced emissions.
- Built from heat-resistant stainless steel for durability.
- Bypass pipes for performance tuning and track applications.
- Restores power, efficiency, and exhaust sound balance.
- Available for classic and modern Porsche vehicles.