This is the exhaust flow meter, which contains several of the sensors the SEMTECH unit uses to analyze the emissions. When building the exhaust system for this car we placed the O2 sensors and the cats along a section of exhaust pipe that fit between the ends of the headers and a "Y" pipe. Y pipes are becoming more common in southeastern Asphalt Late Model competition, so the exhaust configuration was fairly typical of what we'd see at a local Saturday night. We started out with two sections of plain 31/2-inch pipe coming off the headers, then placed two more dummy pipes cut the same length as the catalytic converters and then into the Y pipe. From there, we ran flexible stainless steel tubing back and outside the frame to the flow meter that contained sensors which were hard wired back to the SEMTECH-DS unit. The design goal of the cats is to heat up to a sufficient temperature to ignite any unburned fuel and along with that any harmful emissions that may be present in the exhaust gases.