Adding 'real' power is a tough one on a modern normally aspirated car that's already 'high performance', such as a 997. Even with relatively serious $, including the x51 package, the diffirences are relatively insignificant considered objectively, i.e. real acceleration, speed, etc. The sound/feel is likely to change and make it easier to convince ourselves that the $ were well spent and the car is faster, as per the plenum, but really... Even though there may be a horsepower pick up on the dyno, real world speed is tough to find. If that's really important, I'd simply by a 996/997 TT and play with boost.

 

This statement is so untrue. This would mean that Porsche's X51 makes zero power and torque. Combinations of freer flowing exhaust and software to manage it clearly and irrefutably generate more power and torque. Consider that every race team (club or professional) has installed these types of modifications, and they aren't wasting their time and money just to have louder exhaust notes.