METAL CATALYZER AP2 F22C33005 AH004 The stock catalyzer cell number is about 600cpsi and HKS Metal Catalyzer is 300cpsi.(cpsi= cells per square inch) HKS keeps lower pressure loss by the taper cone shape and lower number of cells. However at the same time we use more catalytic metal to clean the exhaust emission. Most of the exhaust pressure loss occurs at the catalyzer, therefore changing to the Metal Catalyzer is the most efficient method to lower the engine friction loss.