You have heard of the Cold Air Intake, red silicon hose modifications for better sound. This works by removing the intake sound dampening Helmholtz resonator from the air path. It's particularly effective on the standard 997 as it does not have the 997-S vacuum flap at the entrance to the resonator to cut it off for sportier sound. See here for the details on a 997-S: .
You can achieve the same exact effect on the standard 997- without installing the ugly, red, expensive silicon rubber hose - instead by inserting the cap of a Castrol Syntec Oil bottle into the resonator opening.
Use the 5W-40 as it is on the Porsche approved list and you can do this after your next oil change
Simply remove the rubber air hose (via loosening the clamps and pulling it off), insert the cap (top down, this is the only way it will fit), and re-attach the hose. Make sure you take the paper seal out of the cap (!), and use only the plastic portion.
This is an exact, snug fit into the 45mm diameter opening, and the cap has a lip that prevents it from moving into the air box over time. Similarly, when the hose is re-attached, the cap will be held in place by a lip in the hose, so there is no danger for it moving towards the air stream over time either.
The pictures below should make it obvious.
Enjoy the S-type sound - it really comes alive above 4000
