B153 - C152 System Specifications: 3" Diameter Tubing 4" Diameter Tip 304 Grade Stainless Steel ?OUT OF STOCK The Honda Civic Si exhaust is designed for maximum performance with a 3? catback design. Built from T304 Stainless Steel and a straight through muffler design, these systems will give you an improved performance with an aggressive sound that you would expect from a 3? exhaust. Thermal R&D Exhaust systems are designed with quality of sound and manufacturing as our number one goal. Built from T304 Stainless Steel, the fit and finish of our products are designed for performance on both the street and the track. Understanding that the exhaust is the starting point for many builds, our high-performance exhaust will allow additional modifications to perform at their peak. We engineer our products with the goal of achieving the best all-around product for a given application.