I read a thread that linked to magnaflows site concerning pipe size and creating optimal scavening and flow characteristics. It recommended for naturally aspirated engines a pipe size of 2". That's what comes stock. Wouldn't it be better to just put a different muffler (like the devil) on instead of loosing the torque with a 2.5" cat back.

I'm looking for opinions since I've taken the Helix off and put the stock one back on.