Hello all, i am looking into improving my air flow for added performance. How important is it to match the diameter of intake/downpipe/exhaust. Maybe the downpipe doesn't belong with the others but i am looking at one with a Highflow Catalytic Converter, hoping to pass inspection. If that will not pass, is there an advantage to going with the high flow instead of a catless? My other question is does an air intake always improve high rpm at the expense of low rpm power? Also i don't understand how a less restrictive air flow slows down low rpm vs stock intakes if that is the case. Maybe it was the type of car or parameters of the testing from this video?