The K-Tuned 9th Gen Civic Cat Back Exhaust System uses a proven design to reduce restriction and deliver significant power gains, especially in the upper rpm range, where the K engine loves to breathe. We used large diameter 3" mandrel-bent piping, that really is 3" in diameter when measured, to make sure exhaust gases exit quickly. Like the 8th Gen, there is a bit more room underneath the 9th Gen Civic chassis, so we used the additional space to install a large resonator that helps reduce the noise level and smooth out the sound. On the rear section, the oval muffler is just like our others and is fully polished with a 4" double wall slash cut tip. What you can't see is also important, so the interior of all our mufflers is densely packed with a premium sound suppression material that won't deteriorate like cheaper low grade packing will. All the joints and flanges are skillfully TIG welded by hand, and believe us, you really have to see these welds in person to appreciate them.