G-Sport
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The best G-Sport catalytic converters for a custom or high-flow exhaust build are the GESI G-Sport universal converters in this collection: 300 CPSI EPA-approved cores in 2.5-inch, 3-inch, and 4-inch inlet and outlet sizes, with body diameters and overall lengths listed on each part so you can match your piping. For fabrication work, the range also includes a bare substrate and mantle core and transition cones, including one with an integrated O2 sensor fitting.
A catalytic converter cleans exhaust gases while the engine runs, and a high-flow performance converter does that job with a less restrictive core than a typical factory unit, so a tuned exhaust keeps more of its flow. The 300 CPSI figure in these titles is the core's cell density, the number fabricators compare when balancing flow against emissions performance. Because these are universal parts, they weld or clamp into a custom exhaust or downpipe build rather than bolting to one specific car. Measure your piping first, match the inlet and outlet diameter, check the body size against the space under your car, and plan the O2 sensor location and your local emissions rules before ordering.
About the brands
G-Sport by GESI is the specialist name here, focused entirely on high-flow catalytic converter technology for performance exhausts. Its lineup covers complete EPA-approved and EPA-compliant converters in the common fabrication sizes, a substrate and mantle option for builders who assemble their own housing, and transition cones that step piping into the converter body cleanly. That depth in one narrow category is the appeal: you pick the cell density, body size, and length your build actually needs.
GrimmSpeed is the natural companion brand, since its downpipes are built around high-flow converters; the dedicated GrimmSpeed downpipe and J-pipe collection includes V2 GESI-equipped downpipes for Subaru applications. If you are not fabricating your own pipe, a complete GrimmSpeed downpipe is the bolt-on way to get a GESI core.
Invidia is one of the store's biggest exhaust names, known for downpipes and cat-back systems for the WRX, STI, and many other Japanese platforms. Borla covers the cat-back side with stainless systems known for their sound, while MXP offers its own Comp RS and SP cat-backs. Builders can also browse the turbos and superchargers range and Turbosmart boost control parts.
For background on planning a full system, read our overview of upgrading Subaru exhaust systems for performance before you commit to a converter size.
Frequently asked questions
Are G-Sport converters vehicle-specific?
No. These are universal fabrication parts sized by inlet and outlet diameter, body diameter, and overall length. Measure your piping and available space before ordering.
What does 300 CPSI mean?
CPSI is cells per square inch, the density of the converter core. The G-Sport converters here are listed as 300 CPSI and EPA approved or EPA compliant in their product titles.
Will a high-flow converter trigger a check engine light?
It can, depending on the vehicle, sensor placement, and tune. Correct O2 sensor positioning and appropriate calibration reduce the risk, but there is no universal guarantee across applications.
Do I need the transition cones?
Only if your piping diameter differs from the converter body or you need a sensor port. One cone here includes an integrated O2 sensor fitting, which simplifies fabrication when the sensor must sit in the cone.