Is it okay for bolt-on aftermarket exhaust sections to "step-up" in diameter from headers to cat to catback?

(2010-05-30 19:18:41) 1. Doogie Says: I'm redoing the exhaust on my 94 corolla (1.6L 4AFE for what it's worth) with stainless headers and a stainless catback system. All the stock sections are severely rusted together, so they will have to be cut apart for removal. The outlet pipe on most headers available for that car are 1.75". The inlet and outlet for new catalytic converters is around 2 inches. The piping for just about all the catback systems for that car is 2.5". These parts are supposed to be "direct bolt on", so I assume that the flanges will bolt up fine. I'm just concerned that the sections increasing in diameter without adapters could upset flow. I've never messed with exhaust, could someone shed some light on this for me?2. carguy Says: If you're stepping up like you are it shouldn't be a problem. Occasionally the way the air flows will create a problem but i'm sure this system has been checked out in that capacity. Tag: Is it okay for bolt-on aftermarket exhaust sections to "step-up" in diameter from headers to cat to catback?