COBB Tuning GESI Catted Downpipe Bellmouth – 2007-2013 Mazdaspeed 3

Cobb GESI Catted Downpipe Bellmouth — 2007-2013 Mazdaspeed3

The Cobb GESI Catted Downpipe with Bellmouth for the 2007-2013 Mazdaspeed3 replaces the factory downpipe with a high-flow catted unit featuring a bellmouth entry from the turbocharger. The GESI (Government Emissions Specification) catalytic converter maintains emissions compliance while the improved downpipe geometry reduces backpressure at the turbocharger outlet — a direct improvement in turbocharger efficiency and boost onset.

DETAILS

• Platform: 2007-2013 Mazda Mazdaspeed3 MZR DISI 2.3T
• Includes high-flow GESI catalytic converter — emissions compliant
• Bellmouth entry: smooth transition from turbo outlet to downpipe — reduced backpressure
• Improved turbocharger efficiency and boost onset over factory downpipe
• Designed for use with Cobb Accessport Mazdaspeed3 Stage 2 OTS maps
• All gaskets and hardware included

Bellmouth Entry and GESI Catalytic Converter Design

The downpipe is the exhaust pipe immediately below the turbocharger turbine outlet — the most critical section of the entire exhaust system for turbocharger performance. The factory Mazdaspeed3 downpipe uses a restrictive outlet geometry that creates significant backpressure at the turbine, limiting spool speed and peak flow. The bellmouth entry on the Cobb downpipe provides a smooth, gradual transition from the turbocharger’s circular turbine outlet to the downpipe diameter — eliminating the sharp edge and abrupt transition that creates turbulence and backpressure in the factory unit.

Stage 2 Integration with Accessport Mazdaspeed3 Maps

The GESI catalytic converter in the Cobb downpipe maintains the emissions compliance required for street use while providing significantly lower flow restriction than the factory catalytic converter. The GESI catalyst uses a high-cell-density substrate that meets government emissions specifications while offering substantially less exhaust flow restriction than the factory OEM catalyst.

What’s in the Box

• Cobb GESI catted downpipe with bellmouth
• All gaskets, bolts, and hardware

Why Choose Cobb Tuning

Cobb Tuning has been developing performance software and hardware for turbocharged enthusiast vehicles since 1999. Founded in Austin, Texas, Cobb built its reputation on the Accessport and expanded into a full catalog of hardware engineered to complement it. Every OTS map is developed in-house on real vehicles, and every hardware product is validated as part of a complete system — not sourced and sold in isolation. That integrated approach is why Cobb produces consistent, reliable results across the builds we see every day.

The RallySport Take

The Cobb catted downpipe for the Mazdaspeed3 is the Stage 2 exhaust component that the Accessport Stage 2 maps are calibrated around. The downpipe’s improvement in turbocharger efficiency is the most significant exhaust modification available for the MZR DISI 2.3T platform — more impactful than any cat-back change. Pair with the Cobb cat-back for a complete system, and with the Accessport Stage 2 OTS map that accounts for the downpipe’s specific flow characteristics.

Fitment

Year	Make	Model	Notes
2007-2013	Mazda	Mazdaspeed3	MZR DISI 2.3T MT