depends on what you like! you can do it but why not just go with the dual?

 

I am not an expert but, changing a dual exhaust to a single exhaust even with larger pipes, you prob won't see any gain in HP. By reducing the number of pipes, you are restricting airflow. Even though you'll be using a larger diameter, you're only improvement may be sound. Maybe someone else will chime in with the numbers. I know there are some tech heads on here that could probably explain it better.