Here is the difference between the stock hose from a 997 and the Fabspeed Silicone Hose.
The Porsche factory 996 and 997 hoses are corrugated rubber hoses. Fabspeed silicone 4 ply hose is very smooth internally to eliminate boundary layer turbulence and results in an increase in airflow to the engine. Fabspeed eliminated the small side rubber tube that connects to the Porsche muffler/resonator on 996 and on 997 cars.
If anyone is near the Philadelphia area feel free to stop by our facility with a 997 or 996 and I will be more than happy to install a cold air kit with BMC filter and do a before and after dyno. You are more than welcome to contact the guys at BGB Motorsport and see why they use the Fabspeed cold air kit on their race cars. (The wrap on the Factory airbox is a thermal wrap to help keep the intake temps down even more)
The Fabspeed cold air kit gives you great sound by removing the Helmholtz resonator, and when used in conjunction with the BMC air filter you get a nice increase in power through the entire RPM range.