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: http://www.youtube.c...?v=A5dUpmu85Mk.

You can achieve the same exact effect on the standard 996/997 without installing the ugly, red, expensive silicon rubber hose 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 (!).

This is an exact, snug fit into the 45mm opening. 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 sound.

 

Cool trick!

 

Learn something new everyday! Thanks!

 

otherwise known as "orange cap" mod.

 

Thanks - I'm going to try this.

 

...just did it..works great, especially as the revs increase over 4000

 

I just did it but with different bottle cap than what's listed above which also snug fit. It's too late to fire up the car now, will report tomorrow about how it sounds/performs.
thanks for the trick OP

 

update:
It does sound nicer and I can't complain for simple and free mod.

 

Is the "orange/Castrol cap" mod necessary for “S” models if you unplug the vacuum line as shown in the video? Do non "S" models have a vacuum line for the Helmholtz resonator?

 

Does it cut down on the amount of air flow to the engine?

 

I did this on my 996 C4 cab.

 

what I understood that it allows more air to your engine..

 

in the engine compartment melting the plastic cap and sucking it up the intake hose or something. I wouldn't think that the cap would be made of a heat resistant plastic-- am i just paranoid or is this an appropriate concern??

 

..appropriate but not to worry. It is a really tight fit and the cap is lipped and almost "locks" in. In addition, the hose holds it in really snug. Hope that helps.

 

Sure wish something like this could be done to the stock intake on newer 997's. The Helmholtz resonator and associated tract is now "melded" into the air box's intake track, and the stock intake hose is oval shaped instead of round. I've considered performing some major surgery and removing the resonator and the related portion of the intake track then adding a rounded piece of plastic stock to take its place. This would allow the intake track to accept a smoother round section of intake hose similar to what the OP demonstrated for the earlier models, and still maintain a "stock" appearance.