ok i have an astra coupe turbo and have decided to take it to around 290-300bhp with 350+lbs torque. i have a clear idea of everything else but i want to know about sport cats. i know there more free flowing, but why, is the material inside different? what diameter inlet/outlet should i get? whats better..100 cell or 200 cell? any gen would be great, ps im buying the cat alone and welding it in place of the old one, i allready have a cat back and a de cat at the front.