These are high quality, 304 grade stainless steel pair of catless manifolds with primary inlet diameter of 44mm. This upgrade will yield a substantial power increase as well as sound. They do include an internal mini catalytic converter at the downstream 02 sensor as pictured. On my personal vehicle I opted to remove it as I felt it was a significant obstruction. In either form it is recommended that the vehicle be tuned. You might still require 02 sensor spacers to defeat the check engine light.

(This product removes factory fitted emissions systems and is therefore may not be road legal, meaning this is strictly to be purchased for use off road)

Check out the music in the videos of Co-owner Johua's Cayman S with a GT4 3.8 (Thompson )and 3.4(Club) with these headers and exhaust valves open!