The stock catalytic converter will not work with the JDM header because the collector is much larger than that on the stock header. To make this work a new exhaust manifold gasket (aka donut) is needed along with a custom catalytic converter or test/straight pipe. The donut fits onto the collector end of the header. It is the white piece in the pictures. I was mistakenly told by many that the donut from an NSX would fit onto the header. This is not true. The NSX donut is the same size as the one on the stock Integra header. The donut that is needed comes from a 94-95 Legend GS or 93-95 two door Legend. The part number is 18229-SP0-J51. The donut fits perfectly. I also hear that an S2000 donut works (S2000s did not exist when I installed my header so it was not an option in the past). The part number for the S2000 gasket is 18229-PCX-003.
