you would be surprised…but it all does vary from car to car…my setup was 2.25 piping from catless header to tailpipe. no cats in between with a 2.5" dia. 22’ long resonator. I had a terrible terrible rasp. The exhaust and header are same company (Stillen) I added a 2.5" Hi-flow magnaflow spun cat and totally changed my exhaust not a eliminated 90% of the rasp
the cat back helped with rasp that I had with stock catback and header/midpipe no cats