I spent a lot of time at dynos watching people throw on 3" exhaust on their cars and see horsepower drop in the low range and net slower 1/4 mile times. People need to research this stuff instead of just following the gang which happens alot in the enthusiasts world.
'12 Focus Red Candy SE Sport 5 spd
'99 Toyota 4Runner Sport
'11 Subaru WRX STI Hatch