Round Cat - Euro 5 (Double Brick) 400CPICatalytic converters are commonly rated by CPI (Cells Per Inch), which refers to the number of internal honeycomb cells within the catalyst core. The CPI rating affects both exhaust flow and emissions efficiency. 100 CPI Lower cell density with larger passages, allowing maximum exhaust flow. Often preferred for high performance or racing applications where flow is the priority. 200 CPI A balanced option that still flows well while providing improved